174 



NATURE 



{j't:nc 24, icb'o 



EXPERIMENTAL RESEARCHES IN 

 ELECTRICITY i 



ir. 



THE experiments were made in a bell-jar, containing 

 the terminals, which could be gradually exhausted 

 after having been filled with air or other gas. One of 

 the terminals was fixed to the bottom plate, the other 

 could be adjusted to any distance from it by a rod sliding 

 through a stuffing-box in the glass cover. The foot of 

 the stand was insulated by a disk of ebonite, on which it 

 stands. One such bell-jar is 9I inches (23'4 centims.) 

 high, and 54 inches (r4'9 centims) in diameter ; its cubical 

 content, ascertained by covering the open ends with glass 

 plates and filling with water from a graduated measure, 

 was found to be 3,787 cub. centims. 



V2.Z2, whence 



A remarkable phenomenon was observed on making 

 connection between the terminals and the battery by 

 means of the discharging key, namely, that within certain 

 limits of pressure in the bell-jar a sudden expansion of 

 the gas took place, and that as soon as the connection was 

 broken the gas then as suddenly returned nearly, but not 

 quite, to its original volume in consequence of a slight 

 increase of temperature. The effect was exactly like that 



■ '• Experimental Researches on the Electric Discharge with the Chloride 

 of Silver Batterj'," by Warren De La Rue. M.A., D.C.L., F.R.S., and 

 ilugo W. Muller, Ph.D.. F.R S. Continued from p. 153. 



which would have been produced if an empty bladder had 

 been suspended between the terminals and suddenly 

 inflated and as suddenly emptied.' 



The following experiment in rarefied air, at a pressure 

 of 56 mm, at a temperature of i7°-5 C, will give an idea 

 of the amount of instantaneous expansion which occurs 

 when the terminals are connected with the poles of the 

 battery of 11,000 cells, current o'oiio3 W I the resistance 

 of the bell-jar was reproduced by substituting 600,000 

 ohms wire resistance. 



Distance of the terminals — the top one a mm. M- 



point, the lower a disk — 6 in. ; pressure 56 ... 73,684 



On making contact the arc passed and the 



column of mercury was depressed ... IJ'S ... 20.7S9 



Pressure on connection ... 7i"8 = 94,473 

 The increased was to the normal 

 pressure in the ratio of i'282 to i ; as 

 the gas was kept at a constant volume, 

 and supposing the expansion to be due 

 to an increase of temperature, the pres- 

 sure would vary as the absolute tem- 

 perature,- therefore 

 r ^ 7j -8 

 T s6 



T'= 1-282 X 291-2 = 373°-3C.; 

 (373'3-2737)=99°-6C., 

 the temperature of the bell-jar, and 

 (99'6- 17-5) = 82'-!, the rise of tem- 

 perature while the discharge was taking 

 place. But the temperature of the bell- 

 jar as determined by a thermometer 

 inclosed in it with its bulb uppermost 

 only rjse 0° 64 C. per second, taking 

 into account the rate of cooling. It is 

 evident, therefore, that the increase of 

 pressure cannot be ascribed to the 

 instantaneous heating of the bell-jar 

 82° C. 



Taking the dimensions of the arc 

 from a photograph shown in the plate, 

 Fig. 30, it was calculated that it must 

 have attained the enormous tempera- 

 ture of 16,114° C, if the increase of 

 pressure was really due to heat. It 

 was found that platinum wires o-qoi 

 iSJUSjfl inch in diameter supported in various 



'■PP, parts of the arc, as shown in the plate, 



'" i-^ Fig. 30, were immediately fused ; the 



temperature of the arc was therefore 

 as high as the fusion-point of platinum, 

 and possibly considerably higher. 



If the \^hole of the heat evolved by 

 a current of o'oii02 W, through a re- 

 sistance of 600,000 ohms had been 

 communicated to the air in the jar, 

 weighing 0-339 grni-; it would raise it 

 2i5^'6C. in one second. It is known 

 from direct experiment that this enor- 

 mous evolution of heat was r.ot com- 

 municated to any extent to the air in 

 the bell-jar, because its temperature 

 only increased about 0^-64 C. per 

 second ; the heat must consequently 

 have escaped almost instantaneously by radiation. It is 

 difficult consecjuently to realise the conjecture that the 

 enormous dilatation which occurred instantaneously could 

 have been caused by increase of temperature. And it 

 points to its being produced by a projection or scattering 

 of the molecules by electrification causing them to press 

 outwards against the walls of the containing vessel, this 

 pressure being distinct from the motion caused by heat. 



' De la Rive noticed that oscillations occurred in the mercury cf a gauge 

 attached to an exhausted tube as socn as the current passed. 

 ^ Atsoluie zero= 273-7 C, =73 7 -^ '7'S= 29>-2 



