376 Miscellaneous Intelligence. 
A. Measurement of the conductibility of Bodies for Electricity —M. 
Rousseau has, for several years past, been occupied in the construc- 
tion and observation of dry voltaic piles, and has lately applied them 
to the determination of the conducting power of bodies, in regard to 
electricity. MM. Ampere and Dulong were directed by the French 
Academy to report on a memoire by M. Rousseau on this subject, 
and the following statement is drawn up from that report. The dry 
pile is formed of discs of zinc-leaf, and tinsel, separated by discs of 
parchment, previously imbibed with a mixture of equal parts of oil 
of poppies and oil of turpentine ; the whole pile is covered with resin 
to prevent the contact of the air. The pole is fixed vertically com-. 
municating below with the earth, the upper end is made to communi- 
cate at pleasure by awire to a pivot, on which is placed a weakly- 
magnetized steel needle, and alsoto a metallic ball placed at the same 
height as the needle, and not quite half its length from the pivot ; 
hence, when the communication is made the needle and ball are 
similarly electrified and the needle is repelled ; and when the needle 
and ball are previously placed in the magnetic meridian, the position 
to which the needle is repelled is proportionate to the magnetic and 
electric forces, and is constant for a very considerable time for the 
same apparatus. The magnetic needle might be replaced by a simple 
electric needle suspended by a wire of proper length and diameter, 
forming a balance of torsion; but the arrangement of M. Rousseau 
is more convenient, and sufficiently sensible. 
On using the instrument, the substance of which the conductibility 
is to be measured, is made part of the connexion between the top of, 
the pile and the needle and ball, care being taken that the portion: 
traversed by the electricity is always of the same dimensions. If the 
time occupied in producing the greatest deviation is not instantaneous, 
then the period which passes before the needle takes a permanent 
position is a measure of the conductibility of the substance employed. 
Liquids, when tried, are put into small metallic vessels communi- 
cating with the ball and needle, then a wire partly covered with gum 
lac, except for a certain length at the extremity, has that uncovered 
portion entirely immersed in the fluid, so that the same surface is 
always in contact; then, on connecting the other end of the wire with 
the end of the pile, the time which passes before the needle is at its 
maximum deviation is observed, and is inversely as the conducting 
power of the liquid. 
Observing in this manner, a remarkable fact was noticed with olive 
oil, for, notwithstanding its similarity to other oils, it was found to 
be exceedingly inferior in conducting power. ‘Thus all other things 
being equal, olive-oil required 40’ to produce a deviation produced 
in 27’ by poppy and other oils, and on adding to olive-oil only +45 
of another kind of oil, the time was reduced to 10’. Hence any 
adulteration of olive-oil is easily discoverable by the instrument. 
Solid fat conducts with less facility than animal oils, from the ex= 
SS ere 
