480 
MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
Another experiment made with a tube (fig. 3, on the same scale as fig. 1) 075 inch 
AVy. J 
(P9 centim.) in diameter, and 23 inches (58*4 centims.) long between two terminals, 
both paraboloidal in form, gave the following results 
Pressure. 
Deflection. 
Total 
resistance. 
Tube- 
resistance. 
Tube- 
potential V. 
m.m. 
M. 
Cube root of M. 
O 
ohms. 
ohms. 
cells. 
14 
18,421 
26-41 
45 
415,000 
203,400 
5392 
13 
17,105 
25-75 
46 
400,300 
188,700 
5186 
12 
15,789 
25-09 
47 
386,700 
175,100 
4979 
11 
14,479 
24-37 
10 
13,158 
23-59 
48 
374,000 
162,400 
4776 
9 
11,842 
22-79 
50 
348,500 
136,900 
4321 
8 
10,526 
21-58 
53 
313,000 
101,400 
3563 
6 
7895 
19-91 
56 
280,400 
68,800 
2699 
5 
6579 
18-74 
3 
3947 
15-80 
59 
249,600 
38,000 
1674 
2 
2632 
13-81 
60 
239,500 
27,900 
1281 
1 
1316 
10-95 
61 
230,200 
18,600 
888 
0-5 
658 
8-69 
58 
253,300 
41,700 
1811 
0-08 
105 
4-72 
47 
336,700 
175,100 
4979 
0-04 
53 
3-76 
34 
897,300 
685,700 
8407 
The pressure of minimum resistance in this particular case is 1 m.m., 1316 M, which 
is the same as that of the atmosphere at a height of 32 *8 7 miles, where an auroral 
display would be visible at a distance of 546’6 miles. It is evident therefore that not 
only the dimensions of the tube, but possibly also the shape of the terminals, have a 
marked influence on the pressure of least resistance, and it is very probable that in 
the atmosphere where the lateral expansion is practically unlimited, the conditions of 
minimum resistance are different from those which exist even in large tubes. 
The foregoing experiments, which show that the pressure of minimum resistance is 
not absolute for any particular gas, but that it varies with the size and form of the 
vessel containing it, seem to point to the conclusion that the carrier of electricity 
must be ponderable matter, and not the ether as has been suggested. Professor Stokes 
considers it most probable “ that the presence of ponderable matter is necessary for the 
transfer of electricity from one place to another. At moderate exhaustions there are 
plenty of molecules, but they are so close that they hamper one another’s motions. 
As the exhaustion is carried further there are still plenty of molecules, but they ham¬ 
per one another less, and therefore the facility for the transfer of electricity is increased. 
But when the exhaustion becomes extreme, there is a loss in the facility of transfer 
from not having enough molecules ; and as the exhaustion is still further continued, 
it is easily conceived that more may be lost, in point of facility of transfer, than is 
gained by increasing freedom in their motions. In a wide space the impediment to 
