204 On some Electrical Experiments and Inductions. 



the whole of the outside surface, top, bottom, and sides, which is 

 completely engaged by the negative on the two interior surfaces. 

 No free charge is required to hold the engaged lines together ; 

 the condition is similar to the concentric spheres of 52. 



(41,42.) The appearance of positive on $ depends on a partial 

 discharge having spontaneously taken place during the elapsed 

 time, as in 35. 



(43.) The lower cake positive by induction; the upper by 

 partial discharge of a few of the negative lines that pass upwards 

 through the three cakes. It is remarkable that the inductive 

 power is limited in its action to the surface in contact with the 

 surface excited. 



(44.) In this, as in 36., the surface in contact with the excited 

 surface appears to share, to a small extent, its excitement, as if 

 conduction had actually followed very slowly behind induction. 



(45.) The permanent effect on the cylinder was similar to the 

 temporary effect on a conducting cylinder of the same size, the 

 charged B. D, being supposed close to but not touching it. 



(47.) This is a very instructive experiment; there was no 

 actual loss of charge, only an apparent loss, so long as the cake 

 was on the electroscope and the contact surface inductively 

 excited. 



(53.) The large radius of the hoop appendage that characterizes 

 Winter's electric machine gives slow divergence to the electric 

 lines that issue from it. See 53. This gives them, as part of the 

 system of electrical lines that includes the lines between the 

 spark balls, great power of lateral compression upon them 

 previous to the spark. 



The thunder- cloud as a charged surface is an extreme example 

 of the spark-producing power of slowly converging electric lines. 

 (58 «.and58c.) The distribution computed from 58 a. subjected 

 to the equation in 58 c, ought to stand the test. In an ellipsoid 

 or spheroid it might be practicable to execute the calculation, 

 and thus obtain further confirmation of the law of mutual depen- 

 dence of the lateral repulsive and root-pulling or contractile 

 force. 



In conclusion I may mention that the theory of electric 

 lines here given was deduced from Harris's experiments about 

 twelve years ago ; since which time I have been in the habit of 

 applying it to the published results of experimentalists, and thus 

 continually testing it. It is very suggestive of new experiments. 

 Some of the simpler sort of these I have been able to make, but 

 there are others, chiefly with respect to the production of light 

 and mechanical effect, that require greater means and appliances, 

 not to mention aptitude; for to suggest and to execute are spe- 



