PREFACE. 11 



sary for the right using- and managing of it, it is 

 fairly presumed that this will be serviceable. These 

 instructions, it may be as well to mention, are not 

 confined to any particular sort of microscope, but 

 are purposely drawn up in general terms^ in order 

 that some profitable information may be gleaned 

 from them, in the management of any microscope 

 whatever, no matter what may be its optical con- 

 struction. 



From the rapidity with which one improvement 

 has succeeded another, it is necessary, in order to 

 come at a right conclusion as to the relative merits 

 of the productions of different artists, to take the 

 time at which their instruments were fabricated 

 into consideration; for, should some of them have 

 been made three or four years before the others, 

 the latter will in all probability excel the former; 

 whereas, had a comparison been instituted between 

 the simultaneous productions of the artists, the result 

 might have been quite the reverse. 



In the explanation I have given of that remarkable 

 instrument, the Polarizing Compound Microscope, it 

 will be found that I have gone somewhat minutely 



