INDUCTION APPARATUS DESCRIBED. 11 



in falling from 600° to 400° the average loss was 8°-6 per minute ; from 400° to 300° 

 the average loss^was 2°-6 per minute ; from 300° to 200° it was 1°7 per minute ; from 

 200° to 170° it was 1° per minute. This was after the apparatus had been charged 

 for a short time ; at the first instant of charging there is an apparent loss of elec- 

 tricity, which can only be comprehended hereafter (1207. 1250.). 



1193. When the apparatus loses its insulating power suddenly, it is almost always 

 from a crack near to or within the brass socket. These cracks are usually transverse 

 to the stem. If they occur at the part attached by common cement to the socket, the 

 air cannot enter, and being then as vacua, they conduct away the electricity and lower 

 the charge, as fast almost as if a piece of metal had been introduced there. Occa- 

 sionally stems in this state, being taken out and cleared from the common cement, 

 may, by the careful application of the heat of a spirit lamp, be so far softened and 

 melted as to renew perfect continuity of the parts ; but if that does not succeed in 

 restoring things to a good condition, the remedy is a new shell-lac stem. 



1 194. The apparatus when in order could easily be exhausted of air and filled with 

 any given gas ; but when that gas was acid or alkaline, it could not properly be re- 

 moved by the air-pump, and yet required to be perfectly cleared away. In such 

 cases the apparatus was opened and cleared ; and with respect to the inner ball h, it 

 was washed out two or three times with distilled water introduced at the screw hole, 

 and then being heated above 212°, air was blown through to render the interior per- 

 fectly dry, 



1195. The inductive apparatus described is evidently a Leyden phial, with the ad- 

 vantage, however, of having the dielectric or insulating medium changed at pleasure. 

 The balls h and B, with the connecting wire i, constitute the charged conductor, upon 

 the surface of which all the electric force is resident by virtue of induction (1178.). 

 Now though the largest portion of this induction is between the ball h and the sur- 

 rounding sphere a a, yet the wire i and the ball B determine a part of the induction 

 from their surfaces towards the external surrounding conductors. Still, as all things 

 in that respect remain the same, whilst the medium within at o 0, may be varied, any 

 changes exhibited by the whole apparatus will in such cases depend upon the varia- 

 tions made in the interior ; and it was these changes I was in search of, the negation 

 or establishment of such differences being the great object of ray inquiry. I consi- 

 dered that these differences, if they existed, would be most distinctly set forth by 

 having two apparatus of the kind described, precisely similar in every respect ; and 

 then, different insulating media being within, to charge one and measure it, and after 

 dividing the charge with the other, to observe what the ultimate conditions of both 

 were. If insulating media really had any specific differences in favouring or opposing 

 inductive action through them, such differences, I conceived, could not fail of being 

 developed by such a process. 



1196. I will wind up this description of the apparatus, and explain the precautions 

 necessary in their use, by describing the form and order of the experiments made to 



c 2 



