On Draioing Prisms. By Dr. Antliomj. 703 



anything like the amount of detail through a prism which you do 

 through the unarmed ocular. 



My conviction then is, that the prism has done very much— and 

 indeed all it can do — in enahling you to get rapidly and correctly 

 as a sketch the outlines and salient points of your object under 

 examination, to which your more or less artistic eye will have to 

 supply the detail. 



Kow to sum up the evidence for the most useful forms of 

 prism : — 



At the usual ohserving angle of the jMicroscope, and when the 

 object is fairly transparent, Beck or Schroder will do good work, 

 but where there is opacity, then Gundlach is to be preferred, in 

 spite of its inverting the image. 



When the Microscope can he 'placed horizontally, and the 

 objects are suitable, Wollaston's prism gives results of pre-eminent 

 beauty. 



With the Microscope vertical, Nachet's hooded prism, I think, 

 stands alone for making copies of almost all objects susceptible of 

 magnification, and it is especially good when dissections are made 

 under the Microscope by aid of an " erector," as the convenient 

 tilting backwards and forwards of the prism 

 allows outlines to be traced, and then dis- ^^^' •^2^- 



section to be resumed with the most charming 

 facility. 



This review of prisms has been a mere 

 outline, but it has taken up all the time I 

 could venture to occupy. While striving to 

 criticize fairly, and placing most stress upon 

 practical points, I have ventured to show 

 what a long and assiduous use of the prism has effected in my 

 hands : permit me to end with the hope that it may do still more in 

 yours. 



N.B. — Fig. 122 is a woodcut of the Beck prism, which I 

 beUeve has not previously been figured. 



