Desaguliers, John-Theophilus

, an eminent experimental philosopher, was born at Rochelle, in France, on the 12th of March 1683. He was brought to England when about two years of age, by his father, the rev. Mr. John Desaguliers, who, being a French protestant, was obliged to quit his native country in consequence of the persecution which followed upon the revocation of the edict of Nantes, which took place in 1685. He was instructed in grammar learning by his father, and read the classics under him; after which he was sent to Christ Church college, Oxford, where he took the degree of B. A. and entered into deacon’s orders in 1710. The same year he read lectures in experimental philosophy at Hart-hall, whither he had removed from Christ Church, in the room of Mr. Keill (afterwards Dr. Keill) who at this time accompanied the Palatines to New England, in consequence of his being appointed their treasurer. In 1712 he married Miss Joanna Pudsey, daughter of William Pudsey, esq. and, on the third of May the same year, took the degree of M. A. The following year he removed to the metropolis, and settled in Channel-row, Westminster, where he continued his courses of experimental philosophy several years.

On the 29th of July 1714, he was elected a fellow of the royal society, of which he became a very useful member, and was much respected by the president, sir Isaac Newton. His first paper which appeared in the Philosophical Transactions, was published in the 348th number, and contained an account of some experiments of sir Isaac Newton on light and colours, which had been repeated by Mr. Desaguliers, in order to confirm sir Isaac’s theory. He soon after communicated to the society (Transactions, No. 361) a method by which myopes might use telescopes without eye-glasses. Of some experiments which he made with Mr. Villette’s burning-glass, in conjunction with Dr. J. Harris, an account was also published in the Transactions. In 1716 he published a piece entitled “Fires improved; being a new method of building Chimnies, so as to prevent their smoaking.” This was a translation from the French, and involved him in some dispute with Edmund Curll, whom he had employed as his publisher, and admitted to have a share in the book. Curll, in order to promote the sale, had puffed it off in a very gross manner; which induced Mr. Desaguliers to publish a letter in a | periodical paper, called “The Town-Talk,” begun at that time by sir Richard Steele, in which he informed the public, that, whenever his name hereafter “was, or should be printed, with that egregious flatterer Mr. CurlPs, either in an advertisement, or at the title-page of a book, except that of Fires improved, he entirely disowned it.”

The merit of our experimental philosopher had now attracted the notice of the duke of Chandos, who. had before taken Dr. Keill under his patronage, and who became also a patron to Mr. Desaguliers, making him his chaplain, and presenting him, about 1714, to the living of Stanmore parva, or Whitchurch. In 1717 he went through a course of his lectures on experimental philosophy, before king George I. at Hampton Court; with which his majesty was so well pleased, that he intended to have conferred upon him the valuable living of MuchMunden, in Hertfordshire; but that benefice was obtained for another person by the earl of Sunderlancl, who prevailed with a friend to present him with a living in Norfolk, the revenue of which, however, amounted only to 70l. per annum. On the 16th of March 1718, he accumulated the degrees of bachelor and doctor of laws at Oxford. On the 30th of June 1720, he made an experiment before the royal society, to prove that bodies of the same bulk do not contain equal quantities of matter; and, therefore, that there is an interspersed vacuum. He likewise made some experiments before the society on the 30th of March 1721, relating to the resistance of fluids, an account of which was published in the Philosophical Transactions, No. 367. In 1728 he shewed before the royal society a machine for measuring any depth in the sea, with great expedition and certainty, which was invented by the rev. Mr. Stephen Hales (afterwards Dr. Hales) and himself; and of which an account was published in the Philosophical Transactions, No. 405. He continued, from time to time, to exhibit various philosophical experiments before the royal society, and for which he received a salary.

In 1734 he published, in two volumes, 4to, “A Course of Experimental Philosophy.”* On the 30th of January,

| the following year, he communicated to the royal society an attempt to explain the phenomenon of the horizontal moon appearing bigger than when elevated many degrees above the horizon, supported by an experiment. He likewise published this year, in 8vo, the second edition of “Dr. Gregory’s Elements of Catoptrics and Dioptrics,” translated into English by Dr. Brown to which he added an appendix, containing an account of reflecting telescopes, &c. In February 1738, he made some electrical experiments before the royal society; and, in April the same year, he performed some electrical experiments at the prince of Wales’s house at Cliefden; of which an account was published in the Philosophical Transactions, No. 454. In 1739 he communicated to the royal society some thoughts and conjectures concerning the cause of elasticity, which were published in the Philosophical Transactions, No. 454, and contributed various other papers, which were also published in the Transactions. He had the honour of reading his lectures before king George II. as well as the rest of the royal family; and he exchanged the living which he had in Norfolk for one in Essex, which he obtained on the presentation of his majesty. He was likewise made chaplain to Frederick prince of Wales.

When Channel row, in which he had lived for some years, was ordered to be taken down to make way for the new bridge at Westminster, Dr. Desaguliers removed to lodgings over the Great Piazza in Covent Garden, where he carried on his lectures till his death. He is said to have been repeatedly consulted by parliament, upon the design of building that bridge; in the execution of which, Mr. Charles Labelye, who had been many years his assistant, was appointed a supervisor. He likewise erected a ventilator, at the desire of parliament, in a room over the house of commons. In 1742 he published a “Dissertation on Electricity,” by which he gained the prize of the academy at Bourdeaux. “This prize,” Dr. Priestley observes, “was a medal of the value of 300 livres, proposed, at the request of monsieur Harpez de la Force, for the best essay on electricity; and shews how much this | subject engaged the attention of philosophers at that time. The dissertation is well drawn up, and comprizes all that was known of the subject till that period.” Dr. Desaguliers, who is styled by Dr. Priestley “an indefatigable experimental philosopher,” died Feb. 29, 1744, at the Bedford coffee-honse, Covent Garden, where he had lodgings, and was buried March Cth, in the Savoy. He was the first who introduced the reading of lectures in experimental philosophy at the metropolis; and was a member of several foreign academies, and corresponding member of the royal academy of sciences at Paris. His personal figure was not very promising; for he was thick and short, not well-shaped, his features irregular, and extremely nearsighted. In the former part of his life he lived very abstemiously; but in his latter years was censured for an indulgence in eating to excess, both in the quantity and quality of his diet. He translated into English, from the Latin, Gravesande’s “Mathematical Elements of Natural Philosophy.” This work was published by his son J. T. Desaguliers, in two volumes, 4to. He left two other sons: Alexander, who was bred to the church, and had a living in Norfolk, where he died in 1751; and another, named Thomas, who became colonel of the royal regiment of artillery, and equerry to his present majesty, and rose to the rank of major-general.

In Dr. Desaguliers’s character as a divine,*

we find only one publication by him, a single sermon, in octavo, preached before the king in 1717, from Luke xiii. 5. “I tell you nay; but except you repent, you shall all likewise perish.” It was a thanksgiving-sermon; but on what particular occasion it was delivered we are not informed.

If credit is to be given to Mr. Cawthoru, Dr. Desaguliers was in very necessitous circumstances at the time of his decease. In the poem entitled “The Vanity of Human Enjoyments,” Mr. Cawthorn laments his fate in these lines:

"How poor, neglected Desaguliers fell!

How he, who taught two gracious kings to view

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All Boyle ennobled, and all Bacon knew,

Died in a cell, without a friend to save,

Without a guinea, and without a grave."

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