NATURAL PHILOSOPHY. 123 



the best vacua which have been obtained, there is neither discharge, light, 

 nor conduction.* The fact of non-conduction by a very good Torricellian 

 vacuum was first noticed by Walsh, subsequently carefully experimented on 

 by Morgan (Philosophical Transactions, 178-3), and subsequently by Davy 

 (1822) ; the latter did not obtain an entire non-conduction, but a considerable 

 diminution both of light and conducting power. 



From these repeated experiments it may fairly be considered as proved, 

 that, in vacua, or in media rarefied beyond a certain point, electricity will not 

 be conducted, or, more correctly speaking, transmitted, an extremely im- 

 portant result in its bearing on the theories of electricity. 



The gradual widening of the strata, as the rarefaction proceeds, is in favor 

 of the phenomena of stratification being due to mechanical impulses of the 

 attenuated medium, and appears to support the following rationale of the 

 phenomenon given by Mr. Grove, who does not advance it as conclusive, 

 but only as an approximation to a theory to be sifted by further experi- 

 ments. When the battery contact is broken, there is generated the well- 

 known induced current in the secondary wire, in the same direction as the 

 original battery current, to which secondary current the brilliant effects of 

 the Ruhmkorff coil are clue; but, in addition to this current in the secondary 

 wire, there is also a secondary current in the primary wire, flowing in the 

 same direction, the induction spark, at the moment following the disruption 

 of contact, completing the circuit of the primary, and thus allowing the 

 secondary current to pass. This secondary current in the primary wire pro- 

 duces in its turn another secondary, or what may be termed a tertiary, cur- 

 rent in the secondary wire, in an opposite direction to the secondary current. 

 There are thus, almost synchronously, two currents in opposite directions in 

 the secondary wire; these, by causing a conflict, or irregular action on the 

 rarefied medium, would give rise to waves or pulsations, and might well ac- 

 count for the stratified appearance. The experimental evidence in favor of 

 this view is as follows : When a single break of battery contact is made, by 

 drawing a stout copper wire over another wire, the stria? do not invariably 

 appear in the rarefied medium through which the current of the secondary 

 wire passes. This would be accounted for, on the above theory, by suppos- 

 ing that in some cases of disruption the induced spark passes across imme- 

 diately on disruption, and thus completes the circuit for the secondary cur- 

 rent in the primary wire; while in other cases, either from want of sufficient 

 intensity, or from the mode or velocity with which contact is broken, or 

 from the oxidation of the points where contact is broken, there is no in- 

 duced spark by which the current can pass. In the former case there would 

 be a tertiary current in the secondary wire, and therefore striae ; in the latter 

 there would be none. 



But the following experiment is more strongly in favor of the theory. It 

 is obvious that the secondary must be more powerful than the tertiary cur- 

 rent. Xow, supposing an obstacle or resistance placed in the secondary 

 circuit, which the secondary current can overcome but the tertiary cannot, 



*The production of vacua "by carbonic acid, and the increasing breadth of the 

 stratifications with increased rarefaction, was communicated by Mr. Gassiot in a 

 paper, read to the Royal Society, January 13, 1859. I incline to think that oxy- 

 hydrogen gas, with potash, might give a better vacuum than carbonic acid, as the 

 last re>idual portions of the gas would be slowly combined by the discharge, and 

 the water so formed absorbed by the potash. W. R. G. 



