274 On the Stratification of Electric Light. 



they have a strong resemblance to the explosion-pictures, and 

 also to the yellow envelope already referred to as surrounding 

 short sparks ; but, as it seems to me, their analogy to the strata 

 is far from complete. The transverse divisions scarcely ever go 

 entirely across, and have no regularity; the jagged fringes and 

 serrated points which form the outline, are in strong contrast 

 with the smooth and comparatively definite boundary which the 

 light often shows ; but, above all, the markings extend through 

 the ivhole track of the discharge, and there is nothing analogous 

 to the dark space or the blue negative light. In fact the two 

 sets of phsenomena seem to belong to different categories : one 

 is the transfer of matter laterally from the axis of discharge by 

 a vehement repulsion ; the other is a succession, along a certain 

 portion of that axis, of fits of discontinuity in the light-producing 

 power of the current. That power, for a certain further distance, 

 totally ceases, to reappear without any intermission, and with 

 the development of rays of higher refrangibility. It is certainly 

 possible that, in rarefied air, these so-called autographs might 

 assume a similar character; but unless this prove to be the 

 case, I think it will be felt that some further step is neces- 

 sary to complete the explanation. As it now stands, any one 

 who compares a fine set of strata with (for example) the superb 

 drawings of exploded wire in Van Marum's Description d'une 

 Ires-grande machine Electrique, v/ill scarcely admit them to be 

 results of the same action, that of mere repulsive force. 

 ' It has been for some time my own opinion that the strata are 

 caused by these periods of intensity, but in a difi"erent way from 

 that just mentioned, — by the successive zones along the axis 

 becoming charged up to the point of disruption. I feel, how- 

 ever, that any exposition of it must be premature till more facts 

 are collected, and still more till we have a mathematical investi- 

 gation of a current's motion in an imperfect conductor. While 

 such labourers as Faraday, Gassiot, and Grove himself are in the 

 field, we can have little doubt that the harvest will not be long 

 unreaped ; and we may surely expect that some powerful mind 

 will ere long bring within the domain of analysis the hypothesis 

 (which every day confirms) that electricity is, as Grove ex- 

 presses it, " a mode of motion." Such an investigation is, from 

 its correlation to other molecular forces, of the highest import- 

 ance, and will certainly reward most amply its author. 



Armagh Observatory, March 7. 



