ERRORS CONCERNING THE MICROSCOPE. 37 



most conclusive, I deny the accusation. My own eyes, un- 

 happily made delicate by over-study in imprudent youth, 

 have been employed for hours daily over tlie Microscope 

 vnthout injury or fatigue. By artificial light, indeed, I find 

 it very trying ; but by daylight — which on all accounts is 

 the best light for work — it does not produce more fatigue 

 than any other steadfast employment of the eye. Compared 

 with looking at pictures, for instance, the fatigue is as 

 nothing. Nor should any uneasiness be felt at the musccB 

 voUtantes, which may be observed for the first time after 

 using the Microscope. Few eyes are altogether without 

 them, and it is erroneous to attribute them to the Micro- 

 scope, because they may not have been previously observed. 

 The student should early learn to keep the unoccupied eye 

 open, not to screw it up, and distort his countenance, because 

 the sight of other objects confuse him. In a little while he 

 will learn to attend only to the eye looking through the 

 Microscope ; and his studies will be greatly relieved thereby. 

 It is further said that microscopic observation is apt to be 

 very erroneous, and that we can see whatever we wish to 

 see. Undoubtedly men often do see what they want to see, 

 and what no one else can recognise. But this is not the 

 fault of the instrument. So far from the Microscope being 

 in itself deceptive, I maintain that it is less so than the 

 unassisted eye ; and for this reason : all vision is mainly 

 inferential; from certain appearances certain fomis are 

 inferred ; this holds of the eye as well as of the Microscope, 

 the optical principles of which are essentially the same ; but 

 while the physical conditions are similar, the mental con- 



