i84 SCIENTIFIC RECORD FOR 1884. 



fhe Crookes phenomena prove. {Wied. Ann., xx, 756; J. Phys., II, iii, 

 210; PJtil Mag., July, August, 1884, V, xviii, 35, 85.) 



De la Eue and Miiller have studied the discharge of 15,000 cells of 

 the silver chloride battery, using two very slightly convex disks, a point 

 and disk, and two paraboloidal points, the potential being iiicreased a 

 thousand cells at a time. Inspection of the curve, shows that it is con- 

 tinuously concave for the d4sks, while for the disk and i^oint and two 

 points it is concave only for a certain distance and then turns oft" and 

 becomes convex. The intensity of force per centimeter decreases con- 

 tinuously up to 15,450 volts in the case of planes ; but in the other cases 

 the decrease ceases after a certain potential has been reached, and then 

 increases so as to be nearly a constant quantity. At 9,000 volts, and 

 beyond, the potential between a point and a disk is very nearly 9,200 

 volts; hence, if the law holds good, to produce a spark 1*^"" long, 

 92,000 volts ; l" long, 920,000 volts : and a flash of lightning a kilo- 

 meter in length, 920,000,000 volts, would be required. This would, of 

 course, be lessened by the diminished atmospheric pressure at that 

 height. Under a mean pressure of 939,211 M it would require 864,- 

 000,000 to produce a discharge between a cloud a kilometer high and 

 the earth. In an induction coil a spark of 1 inch requires 23,367 volts, 

 1 foot 280,400 volts, and 1 yard 841,230 volts. [Nature, January, 1884, 

 XXTX, 327.) 



Lucas has determined the resistance of the arc i^roduced in the Ser- 

 rin lamp, between two Carre carbons 16™'" in diameter. With a 50- 

 ampere current, the carbons being separated 4™"', he finds the resistance 

 to be 0.58 ohm. (C. B., April, 1884, xcviii, 1040.) 



Schneebeli has examined the radiation from the Swan incandescent 

 lamp at various temperatures, employing the method of Svanberg and 

 Langley. The resistance of the lamp, cold, was 80 ohms. The current 

 strength, the total radiation of the lamp, and the luminous radiation were ' 

 measured, and it ai)i)eared that for each current strength C there exists 

 the following relation: C-R = KW, in which R is the resistance of the 

 carbon at the designated temperature, W the energy emitted by the 

 lamp, and K a constant. If R is constant between 900° and 1,500°, then 

 n2 



is constant. The results show that the resistance of carbon between 

 W 



a red and a white heat is apparently independent of temperature. The 

 absorption coefiicient of the glass globes of the lamp is also apparently 

 independent of temperature. ( Wied. Ann., xxi, 430 ; Am. J. ScL, Sep- 

 tember, 1884, III, XXVIII, 225.) 



The electric light systems exhibited at the Cincinnati Exposition were 

 tested by a jury consisting of Mendenhall, Eddy, French, and Laidlaw, 

 and their report has been published. The dynamometric measurements 

 were made by means of the Brackett dynamometer, specially constructed. 

 The current strength was measured by one of Thomson's current gal- 

 vanometers and a Brackett differential galvanometer. The electro-mQ- 



