SEVENTEENTH AND EIGHTEENTH CENTURIES 165 



was a self-taught man; he had never received any scientific training, and as 

 he knew no Latin, in which language most natural philosophers of that 

 time generally published their works, he was unable in his old age to come 

 into contact with the scientific life around him; he had to depend entirely 

 upon himself. It was the remarkable phenomena revealed by the magnifying- 

 glass that fascinated him from the very beginning; he taught himself to grind 

 lenses, and by diligence and having a naturally delicate touch, he developed 

 this art further than any of his contemporaries. Sparing no pains to find out 

 new methods and combinations, he gave to his magnifying apparatus all 

 sorts of forms, some of them very strange; he tried glass, rock-crystal, and 

 even diamonds for his lenses; but the greatest advance he made was in the 

 manufacture of simple lenses with strong magnification; one such lens, which 

 is still in existence, is said to magnify as much as irjo times. As often with 

 self-taught men, he was extremely jealous of his inventions; he never sold 

 a magnifying-glass nor even lent one to anyone; on the other hand, scien- 

 tists who visited him were permitted to use a number of his instruments, 

 though never the most powerful. It is said that among his property there 

 were found more than four hundred microscopes and magnifying-glasses. A 

 number of them he had bequeathed to the Royal Society of London, of which 

 he was a member and which published most of his observations. Busily oc- 

 cupied to the last, Leeuwenhoek reached the age of over ninety; he died in 

 his native town in 17x3. 



Leeuwenhoek' s investigations 

 Leeuwenhoek's collected writings have quite an extensive range, and their 

 contents are extraordinarily varied. The only connecting link that unites 

 them is the microscopical method; this Leeuwenhoek applied to literally 

 everything that came within his range of vision: crystals and minerals, plants 

 and animals. With respect to the last he developed no special microtomical 

 technique, but he studied and illustrated the details of what he observed. 

 This detailed study, however, he advanced further than anyone of his time, 

 and if he possessed the most powerful magnifying lenses known to his age, 

 he certainly had also the keenest eye. He took exact measurements of every- 

 thing that he examined; unfortunately there was in his time no unit of meas- 

 ure which could have served his purpose, so that he was compelled to select 

 such objects of comparison as he thought suitable — a hair, a grain of sand 

 — and to state his measurements in fractions, often thousandth parts, thereof. 

 He took careful notes of everything that he examined and sent them in the 

 form of letters to the Royal Society, to which he had been introduced by 

 his friend de Graaf, and of which he soon became a member. It often hap- 

 pened that one and the same letter contained a mass of different notes on 

 various observations he had made. It was undoubtedly to his great advantage 

 that he so seldom engaged in theoretical speculations, but only described 



