202 THE MINUTE ANATOMISTS 



the revivification of dried microscopic organisms, while 

 he gave the first notices, or the first worth mention, of 

 rotifers, Hydra, infusorians, yeast-cells and bacteria. 



The microscopes which Leeuwenhoek made for himself 

 were double-convex lenses of various power. So much 

 light was lost that the higher powers were only 

 effective when the object was transparent and directly 

 illuminated by the sun. Leeuwenhoek found that the 

 adjustment of one of his lenses to the object was too 

 hard a task for inexperienced persons, and when he sent 

 preparations to a distance it was his practice to devote a 

 separate lens to every object, and fix everything in its 

 place. His experience showed that the most consider- 

 able discoveries were made with lenses of moderate 

 amplification. 



The Boyal Society formerly possessed a set of micro- 

 scopes and objects, bequeathed by Leeuwenhoek, and 

 described by him as "a small black cabinet, lackered 

 and gilded, which has five little drawers in it, wherein 

 are contained thirteen long and square tin boxes, covered 

 with black leather. In each of these boxes are two 

 ground microscopes, in all six and twenty ; which I did 

 grind myself, and set in silver ; and most of the silver 

 was what I had extracted from minerals, and separated 

 from the gold that was mixed with it ; and an account 

 of each glass goes along with them." ^ This cabinet of 

 microscopes, which Baker had before him when he wrote 

 his Microscope made easy in 1743, disappeared long 

 ago. 



Leeuwenhoek had no means of measuring small 

 lengths with precision, and his estimates are sometimes 

 ludicrously wrong ; his standard of comparison was a 

 grain of sand, which he took to be the hundredth of an 



' Weld's History of the Boyal Society, I, p. 245. 



