I would argue that the gradual improvement of glass as a medium spurred on astronomical progress as much as the ingenuity of
astronomers. Since Hellenistic times, glass was all but taken for granted. Sure, it was expensive early on, but it was everywhere. Starting with beads, then mosaic tile and vessels. By the 1st century B.C. The Roman Empire had developed fairly consistent recipes for glass manufacturing. The apex of this was the development of blown glass. More on why this is important later. I could write pages on Roman glass, but I'll just leave this here: The Portland Vase, layered and hand cut between 5 and 25 A.D.
After the Empire collapsed some 300 years later, Europe was losing the ability to manufacture glass. The local masters were dying out, and the Venetians were clamping down hard on their secrets. They had also clamped down on the supply of natron, the flux used in Roman glass making. They inherited the glass business, and had cornered the market. For the time being, Europe would make do with so called Forrest Glass. Made in glass houses scattered throughout the continent. So called because they were in close proximity to the fuel source: wood. This was fair quality glass, but it wasn't clear and there was a learning curve as a replacement flux was discovered. The impurities added green or brown colour to the product. The Venetian glass could be clear as water, and this along with the now centuries old technique of glassblowing could make something special: the convex lens.
By 1280, the glass makers of Venice (who were by this point isolated on an island to prevent them from a) leaving or getting kidnapped, and b) burning down the city) were manufacturing eyeglasses**. These spectacles were for helping those with feeble vision, or who were far-sighted much like today's reading glasses. By 1466 they were being produced on an almost industrial scale. The Duke of Milan ordered 200 pair in various strengths to last him the rest of his life, and have enough to give out to those who needed them!
Optics theory has been around since ancient Greece, and the Kitab al-manazir (Book of Optics) was written in the 900s by Alhazen based on observation and mathematics. These works, combined with the ability to make and grind consistent quality lenses led to turning theory into product. Those with means could experiment on their own. In 1608, a Dutch optician, Hans Lippershey patented the first telescope after observing children playing with a set of convex and concave lenses. This telescope had a 3x magnification.
I'm going to stop this chapter here, because I need to mention the massive resources glass consumed. Even today the US uses 200 TRILLION BTUs per year making glass. That is about half the industrial energy used per year. It was no different back in time. Limits were placed on production due to deforestation, and it wasn't until coal started being used in the 1600s in England that glass making really took off. Glass was an artisan product and its secrets were closely guarded. Fortunately, the use of coal, and the the invention of the telescope overlap.
**lenses had been known since antiquity, What is mentioned here was the start of spectacles for the common person on a large scale.
"The Development of English Glassmaking 1560-1640" Eleanor S. Godfrey
The MET Museum
"The Medieval Machine" Jean Gimpel
Corning Glass Museum
The following I wrote for a talk given to the The Naperville Astronomical Association on November 4th of this year.
Warren De LaRue was a businessman, creating the first pregummed stamps, and a process for mechanically folding envelopes. He was also a gentleman scientist. You see, back in the early days of the industrial revolution and before, much of the scientific knowledge was attained by the upper class. There were, naturally university positions that were designed for research, but those were in a specific area of study. The wealthy members of learned societies were able to fund their own research and collaborate with each other. That is not to say they were solely responsible for breakthroughs, for instance Joseph Fraunhofer was a glassmaker, who through calamity followed by good fortune was able to invent, among other things a polishing machine for large objectives, and the spectroscope.
Astronomy was a costly endeavor. For example a 6” speculum mirror outfit cost 88 Pounds Sterling in 1864. In 1860 London, an artisan made 14 Shillings a week. (20 to a Pound. ) This is only £36/4s. Per year. This was an OK living wage. Sailors made 15s. Weekly, and an Army 1st Lieutenant £200 yearly. Mind you, officers were still aristocracy at this time. Then you needed a place to set up. Dark skies were not an issue, (sigh) but you really wanted such an expensive item in an enclosed place. Gentlemen who owned them likely had their own observatory. Some who were prolific observers could be offered a move into a proper astronomical society observatory. This happened with Bond and Draper.
Once the telescope was had, you could start making observations. For many, this was not enough. Detailed sky surveys were made and compared, comets discovered, and even new planets. The issue was, the sketches that, no matter how masterfully drawn subjective. Two people observing the same crater on the moon would make slightly different depictions. This was a well understood issue, and some were known for having the most accurate hand. Photography changed this. They now had irrefutable depictions of the heavens. The issue now was how adept of a photographer they were. Many, like Herschel and Draper were photographers as well, however many others like De La Rue were not, the latter honed their skill under the observatory dome.
Louis Daguerre, the French Diorama maker and painter was quite skilled at his craft, that of theatre illusion. He partnered with Nicéphor Niépce the inventor who was able to produce a Heliograph, the direct ancestor to the modern photograph. This didn’t use halides, rather the process in which bitumen pitch hardens at a different rate when exposed to sunlight. In 1822 he created what is now the oldest photograph. It should be mentioned that there had been earlier attempts. Paper coated with Silver salts had been used to produce negative images as early as the late 1700s, but they soon faded when exposed to the faintest light. I will also note that Henry Talbott was in the same circles and discovered a process just after Daguerre published his results.
The problem was permanence of the image. After Niépce passed, Daguerre continued his work and by 1839 had come up with a process in which polished fine Silver was sensitized over Iodine crystals, developed with Mercury and fixed with salt water. This process was patented, the patent bought by the French government, and publicly released “for the good of all men”.
After a short time, John Herschel suggested that hyposulphite of soda be used to fix the image. He also helped spread the phrase "photograph". (I believe due in part because it is easier to say than Heliograph.) Soon after the unveiling of the process it was discovered that Bromine could be used in addition to the iodine and make the process much faster.
In bright sun, without bromine, an image can be struck in about a minute, with the quickener (bromine) the time can be as much as quartered. This soon became standard practice all over the world. In March of 1840 John Draper (who was a driving force making the improvements mentioned above, and correspondent with Herschel) attached a plate to his telescope and took the first photograph of something not on Earth; the Moon. In fact, with the aid of his sons he pioneered many methods of celestial photography. His Son, Henry, carried on his father’s work.
The second body to be photographed was much more difficult; the Sun. The issue was that even with an ISO of around .003, the Daguerreotype is too fast to take a picture without infrastructure. The naked Sun was shown in all its glory in 1845. The French scientists Leon Foucault and Louis Fizeau used similar processes as Draper with a 1/60th second exposure. Eclipses were easier, being the same brightness of a full moon. The first eclipse was captured in July of 1851. This inspired Warren De la Rue, Airy, and Secchi 7 years later to hunt for the Solar Corona. William Cranch Bond, using the new Great Refractor at Harvard photographed the first star, Vega in 1859. His son George Phillips Bond led the way to scientific analysis of stars with the procedures he developed.
By this time, the 1850s, the Daguerreotype was firmly established as THE method of portraiture. (painters would debate this point, but the speed and relatively lower cost of the photographic medium meant more people could buy them). There was a new rising star, however. In 1851, Frederick Scott Archer published his work on a new form of photography; the Collodion process.
Many times faster than the Daguerreotype, this process could produce negative images on glass, which if under exposed could be used as positive images. This proved an advantage for many reasons. Glass plates were far cheaper and easier to keep in usable condition, The chemistry was friendlier to the lungs, and the time required to prepare a plate was considerably reduced. Most importantly for our budding hobby of celestial photography as it was known copies could be made on sensitized paper in infinite quantity.
There were drawbacks, pinholes in the collodion layer could ruin an image if it obscured a subject. There was a limited exposure time as the plate could dry out before the exposure was finished. It was, however like the Daguerreotype grainless and methods of plate preparation were soon developed to address any issues. One more point, if the telescope was to be dedicated to making images, often the lens would be calibrated to the chemical focus, rather than optical. This means that it was achromatic, but more towards the blue end of the spectrum, rather than the middle. This was due to the photo processes of the day being more sensitive to that region. Panchromatic emulsions were not around until 1906.
There were many ideas developed on how to expose the plates, or rather turn the telescope into a camera. One was to simply clamp the plate to the tube, another to make a camera with the telescope as a lens. More importantly was to keep the object in the same spot on the plate, tracking. Tracking must be smooth, and not shake the tube.
There were different solutions to this as well, fine clockwork, both spring and weight driven were devised. One that I like was devised by Draper’s sons. Instead of the telescope moving, the
plate did. As the object moved across the field the holder, powered by a water clock (of all things) moved with it. Exposures of over 90 seconds could be had. Finally, the telescope could be built as a camera, as is still often done.
In the 1870s, the dry plate process was invented. This made glass negatives like collodion, but there was no time limit to the exposures. In addition many plates could be made up at a time and developed at the astronomer’s leisure. This led to the first deep sky photography. In 1880 Draper photographed the Orion Nebula. Over a short span of years, the speed of the emulsion was increased, leading to greater discoveries, both inside and far from our solar system.
Addendum: To the reader, Draper's first photo of the Moon doesn't seem like much. As someone who practices this process, I can imagine the sheer glee he felt when he finally got an image. Daguerreotype plates are still time consuming to make. I have attached a much better, and slightly later image of the Moon taken by Whipple, and another, more modest example taken by the author.
Many of the points made in this section have been touched on in the first part. Here I’ll include greater detail. The lens is a Wollensak 127mm 1200mm FL f/9.5 air spaced achromat. It is coated on the outer surface of each lens. It weighs in at nearly 5 pounds including the bezel. It was made by the Virginville optics company in Virginville Pa, also known at the Surplus Shed. The focus spot is ⅝” at 1200mm. The tube is made of clear pine boards, edge glued to make 12” on a side. 2 sides are cut to 10 ½” while the other two are cut to 12”. The boards were then measured and cut to the hollow pyramid shape, with 6” square on the lesser end (objective) and 12” square on the greater end. The sides were glued and screwed together with 1-2-3 block clamped inside to ensure right angles. Several joins were considered, including rabbet, mortised, and lapped. All these posed problems in either tooling or learning curve. With cost being an issue, the money to try and fail was simply not there, so simple but joints were used. Just before the midpoint of the tube there is an access hatch, it runs for 15” towards the large end. It is held in by machine s
crews and threaded inserts. The lens is housed in an aluminum tophat which acts as a mount, sun shade, and angle adjustment. It is fastened to the body tube by 4 machine screws and threaded inserts. Between the mount and body there is a closed cell foam strip that allows for the lens angle to be adjusted by tightening or loosening the screws. Inside the tube is the shutter and the eyepiece/secondary lens. The shutter is truly the heart of the apparatus, as it allows the near instantaneous image to be flashed across the photographic plate. It consists of a ⅛” brass plate 3”x6” with a 1 1/2“ square opening in the middle. Along each long side is an L shaped brass slide. These were milled from a ¼ x ½” brass bar.
The lens is a Kellner style. The original used Huygens, however the required diameter Huygens could not be found. A Kellner is a single and a doublet lens, where a Huygens is 2 singles. There is a possibility that the lens will heat up and be ruined, however testing has not shown this to be a big concern. It is housed in a brass tube that slides within a bronze flange mount.
A good modification would be an radial focus mechanism. This mount is attached to the body tube on rails, and is adjustable on the x-y plane and angle. The materiel for these were sourced from plumbing fixtures, and machined to shape on a lathe.
The large end has the plate holder. It is a standard design, and is built up out of several pieces of wood to ensure uniformity. This is crucial so that the focus of each plate is the same from holder to holder. The holder attaches to the body via an oak box screwed onto the main body. It is held in by friction.
The GEM mount was fabricated from T-6 aluminum tube, and plate. The right ascension tube is 3” diameter, ⅛” wall tube. It is terminated on the lower end with a plug, which has been turned to fit into a bronze bearing. This tube passes through a brass bearing ring and then terminates with a 3 ½” ⅛” wall tube that has been welded perpendicular to the ascension tube. This tube is the bearing tube for the declination axis. The declination tube is the same material as the R.A. tube. The Dec. tube is terminated on either end with a solid bar of T-6. The lower end is ½” thick with a ½-13 tapped hole for the counterweight shaft. The upper ind is 3” long and is bolted in 6
places to the tube. This plug is held onto the body tube mounting plate by 2 ¼-20 screws and one ½-13 screw. The mounting plate is held in 8 places to the body tube by #12 wood screws.
Attached to the R.A. shaft via a phenolic mounting bracket is the large drive gear. This is made of ½” aluminum, and is 7.62” (decimal is used here due to an uncommon fraction) diameter. It was hobbed out on a lathe using a ½-20 tap and a fabricated holder. The total number of teeth is 480. The rest of the clock drive is attached to ⅛” steel plates mounted onto either side of the R.A. shaft frame. It consists of 2 5:1 bronze gear sets, one idler gear and the 480:1 drive gear. The worm gear is brass ½-20 threaded rod with the ends turned down to match the other shafts. There are two methods of powering the drive. A shaft with a chain sprocket and weights with a friction clutch was the original, and first built method. This worked, however was not ideal for anything but reenacting. A small gear motor was employed with a battery and speed controller. The battery is a 6V 5 AH lead acid cell, and the speed controller is a PWM. This provides the motor with the 3.5V at .5 A it requires to turn the needed speed. All the gears are mounted externally to the unit for aesthetic reasons. There is a pinch hazard, however.
The mount ends were then trimmed to a rounded rather than squared off shape, and painted a ‘burnished bronze” black. Wedge pieces were fabricated to ensure a proper angle of ascension.
In April of 2016, I discovered a man named Warren De La Rue while looking through the London Stereoscopic Company website. He was a remarkable scientist and businessman. My interest was originally because of the stereo views of the Moon he made. My attention was soon drawn to an expedition to Spain he made in 1860 to photograph the total solar eclipse. My research led me to an article in the Illustrated London News that had a woodcut of the research party in Spain. I was fascinated by the instrument used. Further reading led me to research the Kew Observatory’s photoheliograph.
He wrote of the expedition in the Bakerian Lecture of 1862. This lecture was far more than an academic speech, he told of the preparations, the trials of the trip, and the generosity of the Spaniards he came across (it is a fun read, even if you skip the science). It was at this time I resolved to build my own device capable of photographing the sun. I also recalled that in a little over a year, a total solar eclipse would be within driving distance of me. I started more research, and gathering parts.
As with my 19th century photography hobby, I decided early on that the main purpose of this solar telescope would be education both of the use of the device itself, and the techniques of using it, as well as the results of its use. As a reenacting prop it will serve well to provide a way for the public to interact with a 19th century instrument, much like when I set up a camera for them to look through. The benefit of a solar telescope is plain, most reenactments occur during the day.
This will also be a useful scientific apparatus. It is, after all an f/9.5 refractor. The resolving power of the device is yet untested, however initial tests indicate that it should surpass the original, once the many techniques (observing and photographing) are mastered. As with any homemade telescope the various idiosyncrasies will have to be determined and dealt with. Much of the designing involved incorporating adjustability.
I tried to make as close a model as I could of the photoheliograph. Many of the dimensions came from reports to the Kew committee, and photographs of the telescope. I tried numerous time to contact the museum where it is presently on display and was met with limites success. As a result I was left to use the available wood cuts, photographs, and scholarly articles to complete my model. There are some noticeable differences between the copy and the original. Most obvious is the diameter of the primary lens. The Kew was a Ross 3.4” 50”FL achromat. Mine is a 5”. This also means that the objective end is 2” larger than the original to accommodate the larger objective. The focal lengths and viewing end are similar enough to the original to withstand criticism.
The wood used on the Kew device is unknown to me, though I suspect mahogany. The grain appears too coarse for this, however the stability and workability of this wood makes it a likely candidate to me. I chose clear pine for my model. This was a compromise between cost and accuracy. While I briefly considered mahogany it was decided against using it due to cost, but predominantly due to the forestry practices involved in harvesting this wood. I could not in good conscience use a rain-forest wood when one of the inspirations for the project is an avid environmentalist.
When building the device some educated guesswork was required. For instance, the sliding shutter has been described briefly, however material and dimensions were absent. I extrapolated this information from other things such as focal length, eyepiece size, and focus spot size. As it happens, after the shutter was built, I found a letter that describes the original and I managed to get it correct.
The focusing mechanics were also unknown. I decided on a simple friction mount. The other option was a rack and pinion mount, however a proper metal one was cost prohibitive. The other materials were chosen as a balance between cost and historical accuracy. For example aluminum is used for the tracking mount. The original is made of brass. The amusing thing is that the cost of my using brass in 2016 is comparable in cost to De La Rue using aluminum in 1855. I also did not make an exact copy of the mount because of cost. The style is a German equatorial mount, as was the original. In addition, as this will need to be moved around for demonstrations, the cast iron stand is not practical, and a heavy tripod will be used instead.
Working within the limits of component availability I decided not to fret too much over the exactness of the replica. Outwardly, accepting the lens size, the replica is passable. The inner workings are the same, as is the method of observation and recording. I believe in this instance, the spirit of recreating the events slightly surpasses exactness. Pains were taken to ensure authenticity as much as possible. For example, stainless steel, modern fasteners, and the like were only used until proper fasteners were sourced. The only sticking point to this is the use of aluminum for the mount. The mount cost was less than $100, where using brass tube (the original used solid gun metal (bronze)) would be $220 at the least. Perhaps the money will be made available to make a correct mount. Until then the aluminum, painted black will do.
The prototype was built over the month of May 2016, and took the first solar pictures in june. It is roughly ½ scale, made from an entry level Meade telescope. The body is luan plywood. I used a modern 4x5 camera back so that I can use standard holders modified for wetplate. The sliding shutter is a prototype of the one in the full scale model. Originally, the prototype was the only one going to be built. I was going to become proficient using it, then sell photographs to fund the full scale replica. The required focal length lenses were expensive; when I could find them.
The Surplus Shed in Virginville Pa. serendipitously had a special run of 1200mm FL lenses made. There was only a week to purchase the lens before the production run was to begin. I quickly set up a crowd-funding campaign. The second day of the lens sale a donor fronted the bulk of the money to purchase the lens immediately.
While the lens was being manufactured, the research was kicked into high gear. No construction could be started without the lens in hand however. The general dimensions were known, so research into material and costs could be started. In addition, the shutter and secondary lens holders could be built.
The crowdfunding was done using indiegogo.com. This site was selected because of the ease of use and I could choose to take any money raised, even if the goal was not reached. The goal was set at $800.00, of which $345 was raised. I thought his was enough to build the telescope, but not the mount. After the body was completed, approximately $80 remained. This was enough to purchase the aluminum for the GEM mount axis. The remaining material for the mount was donated by a friend who is a machinist and telescope builder. The bulk of the cost was the lumber for the body which came to $42 per side.
Some tooling was needed as well, which came to ~$55. The remainder went to purchase the aluminum, hardware, finishing supplies, and glue. All said, including the $180 lens, the project cost was around $550, the overrun of donations was around $80, and covered by myself.
The eclipse of 1860
In 1858, Warren De la Rue was visiting Russia on a business trip and was introduced to the idea of photographing the 1860 Solar eclipse that was to occur in Spain by Dr. Medler. He also was shown a Daguerreotype of the 1851 eclipse taken by Dr. Busch with the Konigsberg Heliometer.
At first, he was unimpressed with the detail of the Daguerreotype (that is to say the lack of detail of the “protuberances”, not the image itself) and was a little concerned with the practicality of photographing such an event. He was quick to observe that the state of the photographic art and that of celestial photography itself had advanced considerably in the intervening 7 years.
He had determined to make the trip himself, but was limited in instruments to photograph with. He had in his own collection several telescopes with which to photograph, however they were limited in image size, the largest of which would still be too small to overcome any defects in the collodion process. His attention was thus drawn to the Kew Photoheliograph that he had overseen the construction of. At the time it was reliably taking 4” diameter images of the sun regularly. This size was ideal for studying the prominences and large enough to be able to discern the difference between a collodion artifact and a solar one.
Mr. Airy of the Kew Committee offered his services in organizing travel. The Astronomer Royal procured a steamship from the Admiralty, and a sum of 150 pounds was served for preparing for the trip. De La Rue and 4 other men were to travel to Spain in June of 1860. Preparing the necessary articles took a year. This included not only preparation of the Photoheliograph and a new pedestal, but all the chemistry and a portable observatory.
The observatory, at first was to be a simple tent, mostly to act as a darkroom for developing the plates. When it was learned that a steamship was available, this turned into a collapsible wood structure, divided into two rooms. The first had a retractable roof to allow for observations, the second was a darkroom complete with a cistern and sink. The entirety was covered by a heavy canvas awning that was pulled back for observation. The half covering the darkroom was kept wet, and succeeded in keeping the darkroom several degrees cooler than the warm Spanish summer air.
In addition to the Kew instrument, several other pieces of equipment were included. A transit, barometers, sextant, and 3 chronometers were added. A double set of chemistry for photography was made up, as well as reserves to make more in case of emergency. Dry rations were included as well, in case the gentlemen were required to camp. All told almost 2 tons of equipment was packed up.
The journey was not kind to several of the more delicate instruments, especially the chronometers. These were needed for both timing the eclipse, but also finding the exact latitude of the observation site. De La Rue finally double checked the location data by spotting known stars and timing their ascent and measuring the angles needed to locate them. Another hitch was the location that was chosen. A thrashing floor used for preparing grain after harvesting was to be used, however the farmer needed it the day of the eclipse. Once the party explained their purpose in being there, the farmer offered to travel “some distance” to the next floor. He did this without any remuneration for his inconvenience. Several times during the lecture, De La Rue mentions the great lengths the locals, the constabulary, and his own troupe went to to ensure success. Often to some hardship of their own, and always without taking any gifts of gratitude.
Barring a small fire caused by an overenthusiastic assistant, the recording of the eclipse was an uneventful, and total success. Two photographs of the totality were taken, along with several drawings. These provided the necessary proof that the prominence were indeed a solar atmosphere, as suspected.
There were a total of 31 in the party, that split into 2 groups. Airy and his party, including his wife, son, and eldest daughter were one. . The De la Rue party found terrific luck. The whole enterprise was seen as a total success, and the group began referring to themselves as "the Himalaya Expedition". While on the way home, it was decided that everyone involved should be officially thanked, from the ship's crew, to the constabulary and residents of the small town they imposed on, such was the joy they felt in their successes.
It wasn't until 1862 that the official data was released, due to the need for an accurate instrument for measuring the photographs. The device used for measurements was a sliding and rotating stage, each divided into degrees with a magnifying lens for looking at the image. The idea was to reference the crosshairs on the image to give definite 90 degree angles, and measure in minutes of arc, the location of spots, and coronal features. This way, height and width of the prominence could be figured.
Thus ended the first solar eclipse expedition. Subsequent trips to various parts of the Empire were undertaken with Heliographs, and the latest device: the solar spectrometer. Both professional and amateurs alike traveled to view the Sun’s corona.
Chasing the Sun
For the entirety of the Victorian era, British gentleman scientists, gathered in the great halls (and back-rooms) of learned societies, were a driving force in the advancement of astronomy. Much of the research was undertaken by the wealthy. These men could afford the equipment, and had the time to utilize it. It was considered their duty to use their means to promote and advance science.
I have a fascination with the Kew Observatory, in London. It was set up originally so that King George III could watch the Transit of Venus in 1769. The building sat empty until 1842 when the British Association for the Advancement of Science started installing various instruments ranging from self recording magnetometers to a solar telescope. It is, in fact the latter that piqued my interest.
The Sun in the mid 19th century was to become one of the greatest research subjects for several decades. It had been known for centuries that the Sun had changing spots, and through observation during eclipses has an atmosphere of sorts. In the 1850s celestial photography, while in its infancy was gaining a reputation for accurate representations of the heavenly bodies that occupy our solar system.
Sir John Herschel, himself a photographic scientist and astronomer urged, in April of 1854 the construction of a camera with the sole purpose of photographing the sun. He wrote to The British association For the Advancement of Science (BAAS): “With regard to proper preparations of paper, or the use of collodion, &c., the photographic art is now so much advanced that no difficulty can arise in fixing upon fitting preparations,or in the manipulations necessary for multiplying them. But it would be very requisite that many impressions of each day's work should be taken and distributed, and an interchange kept up among observers.” He envisioned several solar observatories located in different longitudes to photograph daily, and share the data so to compare them. Any differences would be apparent.
At the time, the solar corona was a hypothesis, and granulationon the surface was left to the interpretation of an artist. He suggests sensitized paper or “collodionized” glass (Report of the 24th meeting of the BAAS 1853-54) Having researched the state of the art photographic media of the time, he was on the leading edge of scientific photography. He suggested, among other things a “pretty large” 3” objective, a large photographic plate, and crosshairs to measure angles on the disc.
The somewhat ambitious project was taken up by the committee in charge of the observatory at Kew Gardens. Kew had been built some 85 years previous to observe the transit of Venus. The British Association For the Advancement of Science had taken over in 1842. It was being used for chronometer, sextant, and barometer calibration. Kew instrumentation was considered some of the best in the world. Other studies at the time of Herschel’s proposal involved terrestrial magnetism, and meteorological studies.
The man chosen to lead this project was Warren De La Rue. He was a successful businessman, and an avid scientist. Indeed his private observatory boasted many enviable instruments that a college observatory today would want to use. Not only were his scientific and business prowess thought of when choosing him to take this on, but also his use of the new collodion photographic process for photographing the moon and planets. (though later he would wonder if solar photography would better suit the Daguerreotype process). He appears, by all accounts to be enthusiastic about the many scientific endeavours he undertook. It seems he approached this project with gusto, ensuring the best possible outcome.
Design and construction of the solar photographic telescope began in 1854. The Andrew Ross co was hired to build the instrument. The estimated cost was £180. The Kew committee allocated £150, and Benjamin Oliveira, M.P. and fellow of the Society donated another £100 over 2 years. It was finished by the meeting of the Society in 1856. This meeting covered 1855/56. In the meantime, the Kew Observatory was being prepared to receive what by this time was called the Kew Photoheliograph. The electrical and magnetic measuring equipment was consolidated, and wind, solar, and atmospheric clarity were measured to ensure this was the best place for the telescope.
Several changes were made by Ross to the telescope during construction. Initially a separate dome with a darkroom was to be erected, 12 feet in diameter. The focusing screen was to be 8 feet away, as Herschel’s original proposal indicated that the screen be 5 feet on a side. It was decided to use the existing 10 foot observatory dome. During the intervening months, it must of been decided that such a mammoth photograph was not needed, owing to the much smaller 12” screen on the finished telescope.
The report of 1856/57 describes the completed instrument. It is approx. 5 feet long, and pyramidal in shape with the objective end being 4” and the plate holding end 12”. The lens, made by Ross was a 3.4” diameter f/14.7 undercorrected Achromat. The undercorrection was to provide a better chemical focus, eliminating the need to focus optically, then move the plate forward to be on the same plane as the blue end of the solar spectrum.
The design of the telescope was thus: the objective focused to an ordinary Huygens eyepiece. This projected the focused image of the sun onto the photographic plate. By changing the focal length of the eyepiece the diameter of the image could be changed. Also included inside the instrument was a crosshair made of platinum wire and held tight with springs. This was set midway through the focus of the eyepiece. The photographic plate holder was ordinary, as found in cameras of the day.
The mount was a German Equatorial style made of solid gunmetal, a bronze alloy. The angle was fixed, as the telescope mount was a permanent one, and was mounted on a cast iron pedestal inside the observatory dome. The tracking was weight driven clockwork with a conical friction clutch to control the speed. By 1857 the Photoheliograph was installed, and the recording attempts started.