SHORT, JAMES, a celebrated Scottish optician, was born at Edinburgh, on the 10th of June, in the year 1710. Having lost both his parents at the age of 10, he was received into Ileriot's Hospital, where he ex hibited his mechanical talents in constructing book cases with a knife and the few tools which fell in his way. After remaining there two years, he went to the High School to receive a classical education; and in 1726, he entered the University, where, after follow ing the usual course of instruction, he took the de gree of M. A.
His friends were desirous that he should enter the church, and with this view he attended a course of theological lectures; but his passion for mathematics and mechanics withdrew him from his theological studies, and soon engrossed all his time and attention. Mr. Maclaurin, under whom young Short had studied mathematics, saw the bent of his mind, and encourag ed him to prosecute his studies and mathematical pursuits as a profession, Ile accordingly began in 1732 to make reflecting telescopes, and the progress which he made will be best described in the following letter to Dr. Smith from Mr. Maclaurin, dated De cember 28, 173.1.
"Mr. Short, an ingenious person, well versed in the theory and practice of making telescopes, has improv ed the reflecting ones so much, that I am fully satis fied he has far outdone what has yet been executed in this kind.
He has not only succeeded in giving so true a fi gure to his speculums of glass quicksilvered behind, as to make the image from them perfectly distinct, but has made telescopes with metal speculums, which far surpass those I have seen of any other workman.
Ile has made six reflecting telescopes with glass speculums, three of 15 inches focal distance, and three of 9 inches. One of the first is at present in my Lord Islay's hands, with which it is easy to react in the Philosophical Transactions, at the distance of 230 feet. Another of them is in the hands of Mr. .11exander Payne, our professor of Law, with which he easily reads the Philosophical Transactions at the distance of 280 feet. I made some trials with one of the speculums of nine inches, and can read with it very easily in the Philosophical Transactions at the distance of 138 feet; but at that time had not an op portunity to try it at a greater distance. At another
time 1 read with it a much smaller print cross the street, at the distance of 125 feet. It cost him a great deal of trouble to make these of a true figure, and with parallel surfaces, and several, when finished, were found useless by reason of veins that then ap peared in the glass.
In the glass speculums every thing else was very well, only the light was somewhat faint compared with that reflected from his metal speculums. This I take to have been owing to the speculums not hav ing been well quicksilvered, and partly to the thick ness of the glass. For one of them, I observed, had a bri&liter reflection, when fluid quicksilver was ap plied to its back surface than after it was foiled.
After he found the light in these glass speculums fainter than he expected, and also because of the great difficulties in finishing them, he applied him self to improve the telescopes with metal speculums. By taking care of the figure, he finds himself able to give them larger apertures than other workmen do; and, by adjusting the speculums and the whole in strument, he has much improved it.
He executes every part himself, and takes vast pains to make the instruments as perfect as possible, and has made them of' focal distances of two inches and six-tenths, of four inches. of six inches, of nine inches, and of fifteen inches. He perforates the large speculums, and uses a concave little speculum.
By those of four inches focal distance he saw the satellities of Jupiter very well, and read in the Philo sophical Transactions at above 125 feet distance. By those of six inches focal distance he read at 160 feet distance. By those of' nine inches focal distance he read at 220 feet distance. By those of fifteen inches, he and Mr. Bayne have read in the Transactions at 500 feet distance, and have several times seen the five satellities of Saturn together, particularly on the 24th of November and the 7th of December last; which very much surprised me, till I found that Mr. Cassini had sometimes seen them all with a seventeen foot re fracting telescope.