288 NATURAL HISTORY OF ARCTIC ANIMALCULE. 



a lens whose focal distance is the tenth part of an inch, they 

 appear as only so many points ; that is, their parts cannot 

 be distinguished, so that they appear from the vertex of 

 that lens under an angle not exceeding an object If we 

 investigate the magnitude of such an object, it will be found 

 nearly equal to Tol ^ of an inch long. Supposing, therefore, 

 these animalcules of a cubic figure, that is, of the same 

 length, breadth, and thickness, their magnitude would be 

 expressed by the cube of the fraction ^ m , that is, by the 



number , £ that is, so many parts of a cubic inch 



is each animalcule equal to.* 



Leeuwenhoeck calculates that a thousand millions of 

 animalcuke in common water are not altogether so large as 

 a grain of sand. 



SPECIES. 



The animalcule of the Arctic Seas have not been much 

 investigated by zoologists ; but the following, which are 

 mentioned by Captain Scoresby, will give the reader some 

 idea of these creatures :— 



4 



Fig. 1, when examined in the field of adouble microscope, 

 appeared of the size of a grain of coarse sand. It was of a 

 brownish colour, and its movements were in a direct line. 



Fig. 2 was about half the dimensions of the preceding ; its 

 configuration approached that of a globe ; it was of a dark 

 colour, with a species of tail, and in its movements it ad- 

 vanced in a curious zigzag direction. 



Fig. 3 was considerably smaller ; it moved about with 

 amazing rapidity, by sudden starts, pausing for an instant 

 between each locomotive impulse, and then springing into 

 a new direction. 



Rees's Cyclopedia, vol. ii. 



