NATURAL PHILOSOPHY. 187 



glass nothing could be seen but tbe small speck of flour and water, 

 conveyed there on the end of a lucifer match, from a common inkstand, 

 which was nearly full of this vivified paste. I bought several of these 

 microscopes, determined to find out how all this could be done for a penny. 

 An eminent microscopist examined them, and found that the magnifying 

 power was 20 diameter. The cost of a lens made of glass of such power 

 would be from 3s to 4s. How, then, could the whole apparatus be made 

 for a penny ? A penknife revealed the mystery. The pill-box was cut 

 in two, and then it appeared that the lens was made of Canada balsam, a 

 transparent gum. The balsam had been very cleverly dropped into the 

 eye-hole of the pill-box. It then assumed the proper size and transpar- 

 ency of a well-ground lens. Our ingenious lens maker informed me that 

 he had been selling these microscopes for fifteen years, and that he and his 

 family conjointly made them. One child cut the pill-box, another the 

 cap, another put them, together, his wife painted them black, and he made 

 the lens. Dickens 's Household Words. 



NEW KEFEACTOMETER. 



This instrument, invented by Prof. Bernard, and exhibited to the British, 

 Association, was founded on the principle of passing a ray of light throiigh 

 a medium bounded by two parallel surfaces, and might be called the refrac- 

 tometer of separation. When a ray passes through such surfaces, if it be 

 incident perpendicularly, it emerges in the same course. If it be incident 

 obliquely, its emergent course is parallel to that of its incidence. Then 

 the relations which connect the perpendicular distance between, the incident 

 and emergent rays the angle of incidence the thickness of the medium 

 or distance between the surfaces bounding it, the index of refraction is 

 known ; the first two can be observed, the third measured ; and then the 

 fourth, which is what we seek, is a matter of simple calculation. 



Dr. "Whewell expressed the pleasure he experienced at seeing this very 

 beautiful instrument, and was particularly struck with the clear proof 

 arrived at by Prof. Bernard, that the light at the several parts of the solar 

 spectrum, was simple, and not compounded light ; and that thus the view 

 which had been some years since propounded, and which was still enter- 

 tained by some, that the spectrum obtained by the prism, was composed of 

 several superimposed spectra, is proved to be unfounded, and must be 

 abandoned. 



ON SOME STEREOSCOPIC PHENOMENA. 



Mr. Dove, at the British Association, stated that he was chiefly induced 

 to draw the attention of the Section to this subject in consequence of Sir 

 David Brewster having denied at the Belfast Meeting the soundness of the 

 explanation which the author had given of the cause of the appearance of 

 those bodies which exhibited the metallic lustre. This he considered to 



