Hartsoeker, Nicholas

, an eminent mathematician, was born at Goud?, in Holland, March 26, 1656. His father intended him for the ministry, but the young man had an early disposition for contemplating the heavenly bodies, which engrossed his whole attention, and finding, at the age of thirteen or fourteen, that without some knowledge of the mathematics he could make no satisfactory progress in this study, he saved his boyish allowance and presents in money, and applied to a teacher of the mathematics, who promised to be very expeditious, and kept his word. Under him he first learned to grind optic glasses, and at length, partly by accident, was enabled to improve single microscopes by using small globules of glass, melted in the flame of a candle. By these he discovered the animalculse in semine humano, which laid the foundation of a new system of generation.

In the mean time, in obedience to his father’s request, be spent some years at Leyden and Amsterdam in the study of the belies lettres, Greek, philosophy, and anatomy, until 1672, when he resumed his microscopical observations at Amsterdam, and communicated his clisco^ veries respecting the animalcules to Huygens, who published them in the “Journal des Savans” without mentioning Hartsoeker. Hartsoeker, indignant at being thus deprived of the honours of invention, determined to avow | himself the inventor of the new microscope, and the first observer of the animalcules; and sent a letter to that purpose to the same literary journal. The editor, however, had the precaution to send it privately to Huygens, who, after reprimanding Hartsoeker for his rashness in being prejudiced against him by envious and interested persons, drew up a memoir for the journal, in which he did his young friend all the justice he could desire.

Hartsoeker being now at Paris, and observing that the telescopical glasses of the observatory there were not large enough, made some attempts to improve them, which, although not successful at first, procured him the good opinion and encouragement of Cassini; flattered by whom he soon made good glasses of all sizes, and at length one of six hundred feet focus, which, on account of its rarity, he never would part with. As to these glasses of so long a focus, he one day told Varignon and the abbe St. Pierre, that he thought it impossible to form them in a bason, but that by trying pieces of glass intended to be quite flat, one might happen to meet with some that were segments of a sphere of a very long radius, and that he had in this manner met with one of twelve hundred feet focus; that this sphericity depended upon some insensible unevennesses in the tables of polished iron upon which the melted glass is stretched out, or on the manner of loading the gFasses to polish them one against another; and that these trials were more tedious than difficult; which was all he chose at this time to communicate.

In 1694 he published at Paris, his first work, under the title of “Essai de Dioptrique,” in which he demonstrated with great perspicuity the whole theory of that science, as far as regards spherical glasses, for he rejects all other figures as useless. He then adds the methods, many of them peculiar to himself, of grinding and polishing glasses, and the names and quantities of the ingredients to be made use of for forming them; and a general system of refraction, along with his experiments, leading him to the different refrangibiiity of the rays of light, he pretends to have been the first to assign their different velocities as the cause of it. Thus his essay on dioptrics is likewise an essay on the first principles of natural philosophy. He reckons but two elements, one a substance, infinite, perfectly fluid, always in motion, and no part of which is ever perfectly separated from the rest the other a collection of little bodies different insize and figure, perfectly hard and | unalterable, confusedly swimming in the fluid element, where they meet, unite, and become the different sensible bodies. With these two elements he forms every thing, and accounts for the weight and hardness of bodies, as he does elsewhere, from the same system, for their elasticity. There are other opinions advanced by him, which the more advanced state of the science has proved erroneous; but this work at that time procured him the esteem of many men of learning, particularly father Malebranche and the marquis de L’Hopital, who, finding him well versed in the old geometry, would fain have gained him over to the new geometry of infinites, to which they were partial; but he considered it of little service in natural philosophy, and had not a better opinion of any of the more abstruse parts of algebra. Encouraged, however, by the success of his Dioptrics, he two years alter published, at Paris, his “Principes cle Physique,” in which he explains at large the system he had already given in miniature, adding to it his own sentiments and those of many others on some subjects which he had not before handled, the whole forming a course of natural philosophy, which, by avoiding too great minuteness, he has rendered sufficiently perspicuous.

On the revival of the royal academy of sciences at Paris, in 1699, he was named a foreign associate, and was soon after chosen member of the royal society of Berlin, but he never used either of these titles, or any other, in any of the works he afterwards published. It is probable, however, that they were of some service to his reputation at least, especially on the following occasion. Peter the Great, on his arrival at Amsterdam, having applied to the magistrates of that city for a person capable of instructing him in those branches of learning he was desirous of acquiring, they named Hartsoeker for that purpose; and he became so agreeable to the czar, that that monarch would have prevailed upon him to follow him to Moscovy. But the length of the journey for a numerous family, and the difference between the Russian manners and those of the people among whom he had hitherto lived, hindered him from accepting the proposal. The magistrates of Amsterdam, to acknowledge the honour he had done to their choice of him upon this occasion, erected a small observatory for him on one of their bastions, which was a handsome compliment to him, although at little expence.

In 1704, after very pressing solicitations, he went to the court of the elector Palatine, who appointed him his | first ma&ematiciau, and honorary professor of philosophy in the university of Heidelberg. Here he published, in 1707 and 1708, his lectures, under the title of “Conjeetures Physiques,” and then took his leave for a time of the electorate, in order to visit other parts of Germany, or study natural history, and mines in particular. At Cassel he repeated the experiments made by Mr. Hamberg with the landgrave’s burning glass constructed by Mr. Tschirnhaus, but without being able to vitrify even lead, insomuch that he absolutely denied the fact, affirming that what Hamberg took for vitrified gold was a substance issuing from the charcoal tbat supported it, mixed perhaps with some of the heterogeneous parts of the metal itself.

From Hesse Cassel Hartsoeker repaired to Hanover, where Leibnitz, the professed friend of all men of learning, presented him to the elector, afterwards George I. and the electoral princess, the late queen Caroline, who gave him a very gracious reception. About this time, the elector palatine hearing speak of the burning-glass of M. Tschirnhaus, asked Mr. Hartsoeker if he could make him such a one. Upon this he caused three to be cast, and having soon finished them, the elector presented him with the largest, which was three feet and five inches Rhinland measure jn diameter, nine feet focus, and this focus perfectly circular, of the size of a louis d’or, and so ponderous, that two men could with difficulty move it.

In 1710 he published a volume entitled “Eclaircissements sur les conjectures physiques,” being answers to objections, most of which he attributes to Leibnitz; and two years after he published another volume by way of sequel to it, and in 1722 a collection of several separate pieces on the same subject. ^In these three works he attacked, very freely, several celebrated names in the republic of letters, protesting all the while, that if he did not esteem them, he would have given himself no trouble about them, and that they were very welcome to criticize upon him in their turn. But, in spite of this apology, he could not conceal an irritable temper, and considerable virulence in his manner of treating them. Neither Newton, Leibnitz, Huygens, or the other members of the royal academy of sciences at Paris, escaped him on this occasion. The academy, however, notwithstanding such behaviour, tolerated him as one of her members, and considered him as subject to fits of ill humour, while the several members, instead of answering him, pursued their researches. | In the second work he takes up and extends his favourite system of plastic souls. In man, according to him, the rational soul issues its orders, and a vegetative soul, which is the plastic, not only intelligent, but more intelligent than even the rational, immediately executes these orders, besides superintending or carrying on the whole animal oeconomy of the circulation of liquids, nutrition and accretion; operations, in his opinion, above the reach of mere mechanics. But it was immediately objected that rational soul, that vegetative soul, is ourselves, and how can we do all these things without knowing it This difficulty he solves by a comparison, which is at least ingenious. Suppose, says he, a dumb man alone in a room, and servants placed in the adjacent rooms to wait upon him. He is made to understand that when he has a mind to eat, he has only to strike the floor with his stick. Accordingly he strikes, and immediately sees his table covered with dishes. Now how can he conceive that this noise, which he has not heard, and of which he has not even any idea, should have brought the servants to him Hartsoeker, not content with attributing these intelligent plastic souls to men and animals, gives them to plants, and even to the celestial bodies.

The elector Palatine dying in 1716, Hartsoeker quitted the palatine court the year following, when the dowager clectress, a princess of the house of Medicis, in whom a taste for learning was hereditary, returned to Italy, her native country. As soon as the landgrave of Hesse saw him disengaged, he did him the honour to solicit him a second time to come and reside with him. But Hartsoeker thought his days too few to spend in a court, and therefore, removed to Utrecht, where he undertook a course of natural philosophy, and made an extract of all the curious and useful observations buried here and there among a heap of useless matter in Lewenhoeck’s letters. And having received some reproaches from Paris on account of the freedoms which he had taken with the royal academy of sciences, he began to draw up an apology, but did not live to finish it. He died Dec. 10, 1725. Fontenelle says he was brisk, facetious, obliging, but of an easy temper, which his artful friends often abused, and which betrayed him into those critical asperities which are too frequent in his works. ¹

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