176 The Microscope. 



ment is invaluable, for by it the proportion of pure sugar in a 

 given solution can be detected. Lastly, a Nicol prism, so ad- 

 justed that the principal section is vertical, will absorb the 

 polarized rays reflected from the surface of water and thus sub- 

 merged objects, ahead of a vessel at sea, are made visible by the- 

 refracted rays from those objects. 



If after reading these lines some few take interest in the polari- 

 scope, the writer will feel amply repaid. We must not expect 

 to become a Nicol, a Huygens, a Malus, a Biot, a Brewster, 

 or a Fresnel. But after we have used the polariscope we shall 

 at least delight in thinking after these men their thoughts on the 

 abstruse subjects that cluster around polarization. 



NOTES ON THE MICROSCOPE STAND AND ON SOME 

 OF ITS ACCESSORIES. 



AN AMATEUR. 

 • XVIII. 

 THE USE OF THE STAND. 



IT is well for the observer to keep both eyes open M-hen using 

 the- microscope, and if he begin with this plan he will be- 

 doing well, for it is somewhat of a trouble at the start to see any- 

 thing in the microscope with both eyes open, as the unemployed 

 organ seems to dominate. At first the images of the objects on 

 the table and of the object under the microscope will mingle^ 

 but as combination is impossible the result will be amusing and 

 annoying. At one moment the magnified image will have the 

 mastery, at the next tlie macroscopic objects will dominate the 

 view, and at times the e3'e will fail to take cognizance of any- 

 thing. But with a little practice the result is entirely satis- 

 factory, and the brain will finally take notice of the magnified 

 image only. 



It has been- suggested that instead of allowing the unoccupied 

 eye to roam about aimlessly as it does, and as may be noticed when 

 another person is at the microscope with both eyes open, it would 

 be better to give it a dark surface to gaze at, or, as some recom- 

 mend, a white surface. Consequently many forms of eye shades 

 have been devised. They are all applied to or near the eye-piece, 

 a projecting arm carrying a disk for the protection of the unoccu- 

 pied eye. Mr Edward Pennock of the firm of Messrs J. W. Queen. 



