NATURAL PHILOSOPHY. 



19' 



nishes until it retains a perpendicular position. "When thus constrained, the 

 action of the top somewhat resembles the toy under notice, except in its dis- 

 position gradually to right itself, which proceeds from its being already in a 

 position nearly perpendicular. It will be found on carefully experimenting 

 with the new toy, that it sustains itself quietly only when started at or near 

 a level position. If inclined upwards it acts like a top, and rights itself very 

 gradually up until in some cases it loses its hold on the support, and falling 

 upon the table, commences a series of circumgyrations far more vigorous than 

 is consistent with drawing-room etiquette." 



PEEMAXEXT EEPEODUCTIOX OF " XETVTON'S EIXGS." 



M. Carrere has shown to the French Academy that Newton's rings may be 

 reproduced by letting fall on water a drop of a solution of bitumen of Judea, 

 with benzoin and naphtha. It is a curious optical experiment, and the more 

 so, as the film may be taken off the surface of the water on a sheet of paper, 

 and kept, when dry, for permanent observation. 



THE NAPOLEON III. SPY-GLASS. 



The above is the name given to an 

 ingenious contrivance by its inventor, 

 Mr. I. Porro, a retired officer of the 

 Piedmontese military engineers. TVe 

 condense the following description from 

 the Paris Illustration: 



The improvement consists in so ar- 

 ranging a series of prismatic lenses that 

 the larger portion of the spy-glass may 

 be placed in a vertical case ; as, for 

 example, hi the head of a cane. Con- 

 venience in holding, travelling, and 

 economy of space is thus secured, while 

 the power of the spy-glass is, hi some 

 respects, improved. 



A short instrument, like that shown 

 in fig. 2, when held in the hand, is less 

 liable to oscillation, and enables the 

 observer to point it correctly and steady, 

 and to measure by means of an ocular 

 micrometer the distance to a given point, whenever the absolute size of the 

 body observed is known, and vice versd ; it is also very convenient for trans- 

 portation, making a pocket instrument without the usual sliding tubes, 

 which prevent a correct centring of the lenses. 



This spy-glass consists of an objective rectangular prism, fig. 1, ground in 

 the shape of a lens on one of its catheti, and throwing back below, by 

 reflection on its hypothenuse, the horizontal rays from the exterior body 

 observed. These rays meet a second rectangular prism, where, by the laet 



