134 



able adjunct and certainly will aid in giving 

 greater manipulative skill. 



At this point it is considered advisable to add 

 some suggestions from Carpenter. 



" The correctness of the conclusions which the 

 microscopist will draw regarding the nature of 

 any object from the visual appearance which it 

 presents to him, when examined in the various 

 modes now specified, will necessarily depend in a 

 great degTee upon his previous experience in 

 microscopic observations and upon his knowledge 

 of the class of bodies to which the particular 

 specimen may belong. Not only are observations 

 of any kind liable to certain fallacies arising out 

 of the previous notions which the observer may 

 entertain in regard to the constitution of the 

 objects or the nature of the actions to which his 

 attention is directed, but even the most practiced 

 observer is apt to lake no note of such phenomena 

 as his mind is not prepared to appreciate. Errors 

 and imperfections of this kind can only be cor- 

 rected, it is obvious, by general advance in scien- 

 tific knowledge ; but the history of them affords a 

 useful warning against hasty conclusions drawn 

 from a too cursory examination. The suspension 

 of the judgment, whenever there seems room for 

 doubt is a lesson inculcated by all those philo- 

 sophers who have gained the highest repute for 

 practical wisdom ; and it is one which the micro- 



