"I have now finished my third review of the heavens. The first was made with a Newtonian telescope something less than seven feet focal length, a power of 222, and an aperture of four and a half inches. It extended only to stars of the first, second, third, and fourth magnitudes. My second review was made with an instrument much superior to the other, of 85.2 inches focus, 6.2 inches aperture, [Pg 74] and power 227. It extended to all the stars of Harris's maps and the telescopic ones near them, as far as the eighth magnitude. The Catalogue of Double Stars and the discovery of the Georgium Sidus, were the results of that review. The third was with the same instrument and aperture, but with a power of 460. This review extended to all the stars of Flamsteed's Catalogue, together with every small star about them, to the amount of a great many thousands of stars. I have, many a night, in the course of eleven or twelve hours of observation, carefully and singly examined not less than 400 celestial objects, besides taking measures, and sometimes viewing a particular star for half an hour together."
The fourth review began with the twenty-foot, in 1784.
"My brother began his series of sweeps when the instrument was yet in a very unfinished state, and my feelings were not very comfortable when every moment I was alarmed by a crack or fall, knowing him to be elevated fifteen feet or more on a temporary cross-beam, instead of a safe gallery. The ladders had not even their braces at the bottom; and one night, in a very high wind, he had hardly touched the ground before the whole apparatus came down. Some laboring men were called up to help in extricating the mirror, which was, fortunately, uninjured, but much work was cut out for carpenters next day. I could give a pretty long list of accidents [Pg 75] which were near proving fatal to my brother as well as myself. To make observations with such large machinery, where all around is in darkness, is not unattended with danger, especially when personal safety is the last thing with which the mind is occupied; even poor Piazzi did not go home without getting broken shins by falling over the rack-bar.
"In the long days of the summer months many ten and seven foot mirrors were finished; there was nothing but grinding and polishing to be seen. For ten-foot, several had been cast with ribbed backs, by way of experiment, to reduce the weight in large mirrors. In my leisure hours I ground seven-foot and plain mirrors from rough to fining down, and was indulged with polishing and the last finishing of a very beautiful mirror for Sir William Watson.
"An account of the discoveries made with the twenty-foot and the improvements of the mechanical parts of the instrument during the winter of 1785 is given with the catalogue of the first 1,000 new nebulæ. By which account it must plainly appear that the expenses of these improvements, and those which were yet to be made in the apparatus of the twenty-foot (which, in fact, proved to be a model of a larger instrument), could not be supplied out of a salary of £200 a year, especially as my brother's finances had been too much reduced during the six months before he received his first quarterly payment of fifty pounds (which was Michaelmas, 1782). Travelling from Bath to London, Greenwich, Windsor, backwards and [Pg 76] forwards, transporting the telescope, etc., breaking up his establishment at Bath and forming a new one near the court, all this, even leaving such personal conveniences as he had for many years been used to, out of the question, could not be obtained for a trifle; a good large piece of ground was required for the use of the instruments, and a habitation in which he could receive and offer a bed to an astronomical friend, was necessary after a night's observation.
"It seemed to be supposed that enough had been done when my brother was enabled to leave his profession that he might have time to make and sell telescopes. The king ordered four ten-foot himself, and many seven-foot besides had been bespoke, and much time had already been expended on polishing the mirrors for the same. But all this was only retarding the work of a thirty or forty foot instrument, which it was my brother's chief object to obtain as soon as possible; for he was then on the wrong side of forty-five, and felt how great an injustice he would be doing to himself and to the cause of astronomy by giving up his time to making telescopes for other observers.
"Sir William Watson, who often in the lifetime of his father came to make some stay with us at Datchet, saw my brother's difficulties, and expressed great dissatisfaction. On his return to Bath he met, among the visitors there, several belonging to the court, to whom he gave his opinion concerning his friend and his situation very freely. In consequence of this, my brother had soon after, through [Pg 77] Sir J. Banks, the promise that £2,000 would be granted for enabling him to make himself an instrument.
"Immediately every preparation for beginning the great work commenced. A very ingenious smith (Campion), who was seeking employment, was secured by my brother, and a temporary forge erected in an upstairs room."
The sale of these telescopes of Herschel's must have produced a large sum, for he had made before 1795 more than two hundred seven-feet, one hundred and fifty ten-feet, and eighty twenty-feet mirrors. For many of the telescopes sent abroad no stands were constructed. The mirrors and eye-pieces alone were furnished, and a drawing of the stand sent with them by which the mirrors could be mounted.
In 1785 the cost of a seven-foot telescope, six and four-tenths inches aperture, stand, eye-pieces, etc., complete, was two hundred guineas, a ten-foot was six hundred guineas, and a twenty-foot about 2,500 to 3,000 guineas. He had made four ten-foot telescopes like this for the king. In 1787 Schroeter got the mirrors and eye-pieces only for a four-and-three-quarter-inch reflector for five guineas; those for his seven-foot telescope were twenty-three guineas. Later a seven-foot telescope, complete, was sold for one hundred guineas, and the twenty-five-foot reflector, made for the Madrid observatory, cost them 75,000 francs = $15,000.[19] It was ordered in 1796, but not delivered for several years, the Spanish government being short of money. For a ten and a seven foot telescope, the Prince of Canino paid £2,310.