Microscopical Essays, 129 



Care muft be taken not to "let the breath fall upon the eye- 

 glafs, nor to hold that part of the body of the micrcfcope where 

 the glaffes are placed with a warm hand, becaufe the damp that 

 is expelled from the metal by the heat will be attracted and con- 

 denfed by the glaffes, and obftrucl the fight of the object. 



The obferver mould always begin with a final! magnifying 

 power ; with this he will gain an accurate idea of the fixation and 

 connection of the whole, and will therefore be lefs liable to form 

 any erroneous opinion, when the parts are viewed feparately by 

 a deeper lens. By a (hallow magnifier he will alfo difcover 

 thofe parts which merit a further invefligation. 



Every object mould, if pofhble, be examined firft. in that 

 pofition which is moil natural to it : if this circumftance is neg- 

 lected, very inadequate ideas of the [fracture of the whole, as 

 well as of the connection and ufe of the parts, will be formed. 

 If it be a living animal, care muft be taken not to fqueeze, hurt, 

 or difcompofe it. 



There is a great difference between merely viewing an object 

 by the microfcope, and inveftigating it's nature : in the firft we 

 only confider the magnified reprefentation thereof, in the fecond 

 we endeavour to analyfe and difcover it's nature and relation to 

 other objects. In the firft cafe, we receive the impreffion of an 

 image formed by the action of the glaffes ; in the fecond, we form 

 our judgment by inveftigating this image. It is eafy to view the 

 image which is offered to the eye, but not fo eafy to form a judg- 

 ment of the things that are feen ; an extenfive knowledge of the 

 fubject, great patience, and many experiments, will be found 



R neceffary 



