128 PHILOSOPHY OF ZOOLOGY. 



from its situation. There is, indeed, a considerable loss of 

 magnifying power, which may be supplied by the addition 

 of an eye-glass *, or second lens. 



The preceding remarks on the methods of investigating 

 the external and internal characters of animals, indicate the 

 means used in acquiring accurate zoological knowledge. It 

 is now necessary to enquire into the different methods em- 

 ployed in communicating this information to others, and 

 to point out their advantages or defects. Descriptions, 

 drawings and preparations are those in common use* 



1. Descriptions. In attempting to communicate a dis- 

 tinct representation of scenery, it is, in general, necessary 

 to avoid a minute detail of circumstances, and rather to 

 make choice of those prominent characters which have 

 made the deepest impression on our own minds. The use 

 of description in this case, is merely to convey an outline, 

 which the imagination is afterwards to fill up. The end in 

 view, in giving descriptions of objects in natural history, is 

 widely different. Each description is intended to serve as 

 a standard of comparison, and its excellence, consequently, 

 depends on the accuracy and minuteness of details. If we 

 record merely the more obvious appearances of the indivi- 



* Dr BRKWSTER, in his valuable " Treatise on New Philosophical Instru- 

 ments," gives the following directions for fitting up a microscope for in- 

 specting objects in water. " The object-glass of the compound micro- 

 scope, should have the radius of the immersed surface about nine times the 

 focal distance of the lens, and the side next the eye, about three-fifths of the 

 same distance. This lens should be fixed in its tube with a cement which 

 will resist the action of water or spirits of wine ; and the tube, or the part 

 of it which holds the lens, should have an universal motion, so that the axis 

 of the lens may coincide to the utmost exactness with the axis of the tubes 

 which contain the other glasses." 



