PRACTICAL MICROSCOPY. 



without it be for petrological studies merely; and above all 

 do not purchase the extremely trashy foreign separating 



objectives. If you want 

 foreign glasses, there 

 are good ones to be 

 bought buy them. 



After all, there are a 

 few objections to the 

 form of instrument 

 shown at Fig. 23. The 

 body tube is narrow and 

 the field lens of the eye- 

 piece small in propor- 

 tion, so that the field is 

 limited in size ; then, 

 again, the absence of 

 a coarse adjustment 

 may for some purposes 

 be found inconvenient, 

 while the fitting below 

 the stage should be 

 made removable. On 

 the other hand, the short 

 tube gives a larger field 

 when used for photo- 

 micrography, and is also more convenient as a dissecting 

 microscope, lengthening as it does the anterior conjugate 

 focus and giving more room for the needles. 



Recognising these and several other advantages, the 

 author had one specially constructed, as shown in Fig. 24. 

 The draw tube is wide enough to take the full-sized eye- 

 pieces, and when it is fully extended the whole forms a 

 body of the ordinary length. The stage, together with the 

 body, may be rotated round the optical axis in the same 



Fro. 24. 



