The Use of a Simple Microscope. 



25 



Mr. Collins, in which the contrivances for shifting the object- 

 glasses and attaching the polarizing prism greatly facilitate use, 

 and lessen the time and trouble generally taken up in attaching 

 and changing glasses (Fig. 24). The peculiar eye-douche-like 

 form of the caps of the 

 eye-pieces, being of ivory, 

 and forming a side screen 

 to the eyes, is Avell worthy 

 of being generally adopted. 



Many objects that are 

 too delicate to exhibit 

 their structure under ordi- 

 nary light, become richly 

 and beautifully coloured 

 when seen with polarized 

 light, and are then easily 

 made out. Manv animal 

 and vegetable substances 

 are remarkable for this 

 property, but most, if not 

 all, forms of lime in its 

 crystallized state are thus 

 readily now detected. No 

 instrument is considered 

 complete without its po- 

 larizing apparatus, and the 

 facility with which this 

 can be adjusted, in the pre- 

 sent form, renders it a very 

 desirable addition. 



There are many other makers of good instruments, but 

 sufficient has been said to point out the chief merits of such 

 instruments, in a graduated series ranging in price from the 

 lowest to the highest and most elaborately finished, so as to suit 

 the means or inclination of different persons,* All the better 

 class of instruments are now so constructed, that by obtaining a 

 n-ell-made stand in the first instance, which would be the most 

 politic proceeding, any additional portions may be added at any 

 time afterwards when required ; and by the adoption of a uni- 

 versal screw, the object-glasses of all makers fit into any maker's 

 instrument. 



With respect to object glasses but little has been said, as it is 

 always desirable to obtain the advice of, or to leave the selection 

 to, an experienced microscopist. It should, however, be observed 



Fig. 24. 



We are indebted to the various makers for the use of the blocks employed. 



