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 apartment has more the appearance of a hall of congress than of the auditory of a professor; and as we pay him generously, he, in return, spares no pains to entertain us, and to discover to us all the hidden springs of nature. Physics (properly so called), mechanics, hydraulics, hydrostatics, optics, astronomy, are all included in his course. You have, I believe, in your valuable library, that work of the Doctor’s which is called A Course of Experimental Philosophy; it forms the basis of his lectures. Among the great number of his machines, there are none that excites my admiration so much as his famous Planetarium. I had before seen, in the libraries at Leyden, and Berlin, and elsewhere, several spheres made to exhibit to the eye the motions of the heavenly bodies; I have likewise examined that which they call the Orrery, after Lord Orrery, its inventor. But all these machines, though ingenious, have one considerable defect. For, by placing the sun in the centre, and giving it the size of an orange, it is necessary, in order to preserve a due proportion between it and the planets, and to determine the just distances, and such a sphere should be at least an English mile in diameter. Dr. Desaguliers, perceiving this inconvenience, ruminated for a long time in order to find out some method of perfecting this machine, and at last contrived his Planetarium. He was very efficaciously assisted in this business by Mr. Graham, the most able and the most celebrated watchmaker that ever existed. When the whole machine is complete, you see the sun immovable in the centre, and the earth and moon, and the planets with their satellites, which turn round the sun on their axes. He then begins by turning a winch, and immediately the whole heaven is in its natural motion, each body describing its proper orbit, whether circular or elliptic. The first lecture is given by daylight, that the auditors may clearly observe all the different bodies and their movements. In the next lecture, he places in the centre a small crystal globe, which contains a lamp, and represents the sun. He then shuts the windows, and putting his Planetarium again in motion, he shows in this lecture what parts of the earth, moon, and planets are illuminated by the sun at every instant. In these two lectures (you will observe) the exact distances must be abstractedly considered, for it is not possible to represent them distinctly in a machine of four feet diameter. But in the succeeding lectures, the Doctor analyses his machine, and presents to his auditors the sun still in the centre, but with only one planet and its satellites at a time. By this method, the distances become more discernible; and in this manner he explains with admirable facility the whole solar system. All these matters are exhibited with so much perspicuity, that I would engage to teach astronomy, by the help of the Planetarium, to any lady who has the least curiosity and attention, in a month’s time. But such a machine is not to be had by every one; for that of Dr. Desaguliers has cost him more than one thousand pounds sterling.

The academy of Bourdeaux, at the request of Monsieur Harpez de la Force, offered a medal of the value of three hundred livres (£12) for the best essay on electricity. In 1742, Dr Desaguliers’ “Dissertation on Electricity” won the medal. Priestley, in his “History and Present State of Electricity,” remarks —

“To Dr Desaguliers we are indebted for some technical terms which have been extremely useful to all electricians to this day, and which will probably remain in use as long as the subject is studied. He first applied the term conductor to that body to which the excited tube conveys its electricity — which term has since been extended to all bodies that are capable of receiving that virtue. And he calls those bodies, in which electricity may be excited by heating or rubbing, electrics per se.”

It was in 1738 that Desaguliers made his first electrical experiments before the Royal Society, which he said he could have done at an earlier date; “but he was unwilling to interfere with the late Mr Stephen Grey, who had wholly turned his thoughts to electricity, but was of a temper to give it entirely over, if he imagined that anything was done in opposition to him.” Desaguliers was also the author of numerous papers in the Philosophical Transactions from the year 1716 to 1742, on prismatic colours, on the atmosphere, on the barometer, on magnetism, on electricity, on statics, on perpetual motion. He also published translations from foreign authors, such as Ozanam, &c.

The Doctor continued to lecture with great reputation till his sixtieth year, the year of his death (1744). He spared no expense in procuring illustrations for his lectures. Like many sedentary men, he had an unnatural appetite for food. So that hfs mind may have given way during his last months; and he may also have been embarrassed in his pecuniary affairs. But Cawthorn’s rhapsody in his “Vanity of Human Enjoyments” must be a tremendous exaggeration:—

