Itidmtion Apparatus described, 293 



re-attachment of the stem to the upper hemisphere the ball h 



Fig. 2. 



mmm 



might have the same relative posi 

 tion, a gauge p (fig. 2.) was made of 

 wood, and this being applied to the 

 ball and hemisphere whilst the ce- 

 ment at m was still soft, the bearings 

 of the ball at q </, and the hemisphere 

 at r r, were forced home, and the 

 whole left until cold. Thus all diffi- 

 culty in the adjustment of the ball in 

 the sphere was avoided. 



1191. I had occasion at first to 

 attach the stem to the socket by other 

 means, as a band of paper or a 

 plugging of white silk thread ; but 

 these were very inferior to the ce- 

 ment, interfering much with the in- 

 sulating power of the apparatus. 



1 192. The retentive power of this 

 apparatus was, when in good condi- 

 tion, better than that of the electro- 

 meter (1 186.), i.e. the proportion of loss of power was less. Thus 

 when the apparatus was electrified, and also the balls in the elec- 

 trometer, to such a degree, that after the inner ball had beenin 

 contact with the top k of the ball of the apparatus, it caused a 

 repulsion indicated by 600° of torsion force, then 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 l°-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 electricity, which can only be comprehended 

 hereafter (1207. 1250.). 



1193. When the apparatus loses its insulating power sud- 

 denly, 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. 

 Occasionally 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. 



