Intelligence and Miscellaneous Articles, 147 



follows the same course as the expansion, and is of the same order 

 as is required by the expansion. 



The changes of volume of gases are treated in conclusion, which 

 Quincke could not observe, even with very accurate instruments, 

 or only in one case with carbonic acid. The author doubts the 

 validity of the calculation made by Lippmann (Mascarb and Joubert's 

 ' Electricity,' translated by Atkinson, vol. i. p. 632) on the basis of 

 the principle of the conservation of electricity, which gives for 

 carbonic acid 40 times as great a contraction as that found by 

 Quincke, and also for other gases contractions which Quincke 

 could not have overlooked. 



From the same principle the author deduces that ideal gases 

 could not show any change of volume. — Inaugural Dissertation, 

 Groningen ; Beiblatter der PhysiJc, No. 11 (1890). 



THE OPTICAL USEFUL EFFECT OF INCANDESCENT LAMPS. 

 BY E. BLATTNER. 



The total energy imparted to an incandescent lamp, and in a 

 stationary condition radiated by it, is A = rY. This energy con- 

 sists of two parts, A x and A 2 , which correspond to the radiation 

 of heat and light respectively. If I is the mechanical equivalent 

 of heat, and W x and \V 2 the corresponding quantities of heat, 

 A^IW, and A 2 = 1W 2 . The optical useful effect is A 2 /A = W a /W 

 and W =W 1 + W a . The author determined W by placing the 

 incandescent lamp in a thin copper cylinder blackened on the 

 inside, which was filled with water and served as calorimeter, and 

 which measured the rise of temperature. Wj was measured by an 

 exactly corresponding glass cylinder. 



In order to measure i a special form of compass was used in front 

 of the magnet ; in the horizontal plane laid through the two poles 

 of the magnet a wire rectangle was laid traversed by a current the 

 sides of which run N.S. and E.W. ; the former only act, and in 

 opposite directions ; by altering the distance from one another 

 and from the magnet, the sensitiveness may be regulated. 



If u is the angle of deilexion, a half the length of the sides of 

 the rectangle, d x and d 2 the distance from the magnet, H the 

 horizontal component of the earth's magnetism, the intensity of the 

 current is 



• H, n 2a 2 + d, 2a 2 + d 2 



i= _tanw, C= , * — 2 . 



C djp+dfl d^d' + df) 



The difference of potential was measured partly by shunting 

 and partly with the condenser, where it was compared with 10 Da- 

 rnells. The intensities of the light were determined in standard 

 candles with Bunsen's photometer. The following results were 

 obtained : — 



