468 



Microscopical Essay s. 



in length about half the diameter of the middle of their bodies. 

 Before he difcovered this expedient, he tried to kill them' by 

 different kinds of la Its and fpirits ; but though they were deftroyed 

 by this means, their fins were fo contracted, that he could not „ 

 diftinguifh them in the leaft. After lying in this ftate of torpidity 

 for two or three minutes, if a drop of clean water be applied to 

 them, they will recover their fhape, and fwim about immediately, 

 rendering their fins again invifible. 



It is one of the wonders of the modern philofophy to have 

 invented means for bringing creatures,- fo imperceptible as the va- 

 rious animalcula, under our cognizance and inflection. One 

 might well have deemed an object that was a thoufand times too 

 little to affect our fenfe, as perfectly removed from human dif- 

 covery ; yet we have extended our fight over animals to whom 

 thefe would be mountains. In reality, the greater number of 

 microfeopie animalcula are of fo fmall a fize, that through a lens ? 

 whofe focal diftanee is the tenth part of an inch, they only ap- 

 pear as fo many points ; that is, their parts cannot be diflinguifh- 

 ed, fo that they appear from the vertex of that lens under an 

 angle not exceeding the minute of a degree. If we invert igate 

 the magnitude of fuch an object, it will be found nearly equal to 

 of an inch long, Suppofing, therefore, thefe animalcula to 

 be of a cubic figure, that is, of the fame length, breadth,, and 

 thicknefs, their magnitude would be exprefled by the cube of the 

 •fraction WUj that is, by the number ■ 10 oooooooo6ooo»o ) that is* 

 each animaleulum is equal to fo many parts of a fquare inch. 

 This contemplation of animalcula has rendered the idea of inr 

 definitely fmall bodks very familiar to us ; a mite was formerly 

 thought the limit of littlenefs, but we are not now fui prized to 



