1868. | Physics. 265 
Naval Department. The Secretary has finally reported against 
petroleum ; the only advantage thus far shown is a not very im- 
portant reduction in bulk and weight of fuel carried. 
Execrricity.—H. Poggendorff has published an account of a 
new electrical phenomenon observed by him. This physicist was 
experimenting with exhausted tubes contaiming a certain quantity 
of mercury, having either at one end or both, platinum wires, when 
he encountered the phenomenon. More precisely the circumstances 
under which his first observation was made were the following :— 
A tube of the kind described above, containing only one wire, coated 
towards both extremities with a broad band of tinfoil, was placed 
as an exhausted double jar across the electrodes of a Holtz’s machine. 
While the tube lay in this position on the electrodes, there appeared 
to be a certain motion in the mercury. As this motion could have 
no definite character, the current in such a jar being an alternating 
one, another tube was made provided with platinum wires at both 
ends, and the current passed through the length of the tube, the 
tube being placed as far as possible horizontally. In this case a 
more decided motion of the mercury was observed, but still scarcely 
as decisive as could be desired. A third, fourth, and fifth tube 
showed the phenomenon in about the same degree. A sixth tube, 
however, removed all doubt. ‘This had not only been carefully 
exhausted, but the mercury in it had been kept briskly boiling for 
some time; the mercury was kept out of contact with the platinum 
wires by the tube being bent at right angles at about an inch from 
each end. The tube thus prepared was hung by wire hooks to the 
electrodes of the machine, in such a manner that the body of it was 
perfectly horizontal, the mercury serving as a level. Ags soon ag 
the adjustment was properly made, the machine was set in action. 
When the current passed through the tube, the mercury rapidly 
travelled from the negative to the positive pole. However the 
current was sent, the result was always the same. In experiment- 
ing, the mercury was generally made to occupy a thread of about 
4 inches in length; the horizontal part of the tube was about a 
foot in length, so that the thread had to move over a space of 
8 inches. Two or three seconds was the time generally occupied 
by the mercury in travelling from one end to the other. The 
thread changes shape as soon as it commences to move, becoming 
considerably longer ; the elongation amounted in these experiments 
to an inch. ‘The quantity of mercury set in motion was one 
ounce; very small quantities of the metal will not move, probably 
a result of adhesion. 
H. Poggendorff also believes himself entitled to state generally 
that the electro-negative metals, platinum, gold, palladium, silver, 
&c., render the following insulators positive by friction, while the 
