HARTSOEKER, NICOLAS, a Dutch natural philosopher, was born at Gouda in 1656: his father, who was a minister of the Reformed religion, intended that he ahould eater the Church as a profession ; but a taste for the sciences, which the youth early evinced, prevented this intention from being carried into effects From the money which was allowed him by his father, young Hartsoeker saved money enough to pay the fees of a teacher of mathematics; and ho pasted the greater part of each night in studying the subjects connected with the instruction which he received by day.
An accidental circumstance is said to have directed his attention to the construction of optical instruments : having presented a filament of glass to the flame of a candle, ho was surprised to observe that the extremity, when melted, assumed a spherical form ; and he imme diately conceived the idea of using such spheres as objeot•glasecs for microscopes. In an account which he published in 1678 of the instru menta thus formed, he asserts that he discovered the animalcules which exist in anima fluids {Leuwesnozeg]; and, with the like instruments, Worm Is said to have first perceived the red globules in blood.
In 1674 Ilartseeker was sent to pursue his theological studies at Leyden; and io that city be became known to Iluygbens, who encou raged him in the prorecutlou of hi? microscopical observations. The two philosophers subsequently went together to Paris, where Hart Rooker was introduced to Cassini, who recommended hint is exorcise his ingenuity In the formation of object. glasses for telescopes; and it appears that, after several frulth es cemays, he succeeded in obtaining some which were superior to any that had been before executed. These were of about 600 feet. focal length ; and In order that they might have truly spherical forms, be first, by MORTIS of rand, made a very shallow ezeavation in a plate of glass; theta giving, by the like moans, a slight convexity to one Ade of the plate of which the intended object-glass was to he formed, he placed the convex aide of the latter In the cavity of the other, and by friction brought the contiguous surfaces of both plates to equal and consequently (inherit:el figures. In 1691 he published his ' Eeettl de Dioptrique,' 4to, Paris, in which, beaielea treating of the science, he attempted to give a general theory of tho laws of nature respecting the hardness, elasticity, transparency, fie., of bodies. These aubjects were afterwards explained In detail iu his Priocipes de Physique,' which he published in 1695. The work was criticised by a writer In the 'Journal des Sevens' in the mule year, and 11nrtmeker seems to have revenged himself by makins a violent attack on the Mdmoirea do l'Acaddmie des Sciences.' The attack however remained unnoticed. It appears to have been the character of Hartsoeker to seek occasions of entering into discussions with his friends; and he at length lost the good opinion of the patient Leuwenhocek by urging captions objections to the results of some of his experiments.
Ilaviog become embarrassed in Ills circumstances, Hartsoeker was obliged, in 1696, to quit Paris. He retired to Rotterdam, where he published the work above mentioned ; and he afterwards removed to Amsterdam. At this time he was introduced to the Czar Peter, then travelling incognito, and he was appointed to give the monarch lessons in mathematics. His conversation was so agreeable to the czar that the latter invited him to Russia. Hartsocker however declined leaving Amsterdam, and the magistrates of the city built for him an observa tory in one of the bastions.
The elector palatine having repeatedly offered Hartsoeker the place of professor of mathematics and philosophy at Dusseldorf, he at length accepted it, and in the year 1704 he wont to reside in that city. While be held this post he made several journeys to different parts of Ger many iu order to visit the learned men of the country; and at Hanover he was preaanted to the elector by the celebrated Leibnitz. On his return to Dusseldorf he caused three burning-lenses similar to those of Tschirnhauseu to be executed. On the death of the elector palatine, Hartatteker, declining the aolicitation of the landgrave of Hesse-Cassel that he would reside in that city, retired to Utrecht, where he died in 1725. He bad been admitted a foreign associate of tho Aeaddmie des Sciences of Paris iu 1699; and he was also a member of the Academy of Berlin.
Hartsoekcr is said to have entertained at one time an opinion that there existed in every animal a plastic soul which was charged with the preservation and development of the individual. He is said to have maintained also, and the opinion was probably founded ou a more rancid idea expressed by Plato in the Timms, that from the divinity descended a succession of intelligent beings, the lower orders of which directed and preserved the universe; he had moreover some wild notions respecting an empire which he imagined to exist in the interior of the moon.
In 1722 Hartsoeker published a work entitled Recueil de plusieurs Mem de Physique, oh l'on fait principalement voir l'Invalidit6 du Systeme de Newton.' He also caused a letter to be printed in the 'Journal des Sevens,' containing some absurd remarks on the hypothesis of the English philosopher. He treated Leibnitz no better, attacking with great violence his system of ' monads' and of a 'pre-established harmony.' He would never admit the advantages of the ' Infinitesimal Calculus,' and persisted in considering it as an unintelligible jargon by the aid of which certain learned men nought to increase their reputation. He is characterised by J. Bernoulli as a superficial and an arrogant man ; but his violence is supposed to be lees owing to envy than to a morbid taste for dispute.