Chemical Science. _ 161 
’ 5. Electromagnetic Multipliers —Dr. Kaerntz has lately been oc- 
cupied in proving experimentally the amount of the advantage ob- 
tained in electromagnetic multipliers, by each additional circumvo- 
lution of the wire. His motor was a zinc plate about eight inches 
long and four inches wide, the copper opposing both sides was 
consequently double that'size. The fluid conductor was a solu- 
tion of muriate of ammonia in spring water, with the addition of 
one hundredth of sulphuric acid. The connecting wire was cop- 
per harpsichord wire, covered with silk thread, and the same 
length was used in every experiment. By connecting the plates 
with the wire before immersion, by immersing slowly and by other 
expedients, any important variation in the intensity or quantity of 
action was avoided. 
In this way it was found that the quantity of power of the in- 
strument over the needle, was exactly in proportion to the number 
of convolutions, six convolutions giving six times the power of one 
convolution; and by experiments, when the forces of the instru- 
ment and of the earth’s magnetism were arranged in different 
ways, this result was confirmed. Such an instrument is therefore 
wore correctly called a multiplier than a condenser.—Phil. Mag. 
xii, 441, 
6. Plate Electrical Machines.—A variation in the construction 
of plate electrical machines has been devised and practised -by 
M. Metzger of Siblingen in Schaffhouse, which would seem to be 
areal improvement. Considering that the effect desired in using 
the machine was first highly to excite the glass, and then to col- 
lect the electricity from it, M. Metzger concluded that the dis- 
tance between the rubber and the points of the conductor in ma- 
chines of the common construction was injurious in its effect, not 
only by causing the dispersion in part of the electricity excited, 
but by uselessly wasting the exciting surface. Plates were - 
therefore mounted in a very compact and perfect manner, with 
three pairs of rubbers placed at equal distances from each other ; 
the conductor also had three arms furnished with points a little in 
advance of each pair of rubbers, to collect the electricity in the 
usual manner. ‘The rubbers were not attached to a surrounding 
frame, but to brass arms, which proceeding froma socket through 
which the axis passes, diverged at equal distances from each other 
towards the periphery of the plate. The machine has a very com- 
pact and neat appearance, and its various smaller parts are con- 
trived with much judgment. 
In some comparative experiments made with a plate twenty-two 
inches in diameter, the superiority of three pair of cushions over 
two pair was very manifest. In the following table the first 
column expresses the length in inches of the rubbers; the second 
the length of the spark when two pair of rubbers were used, and the 
Vor, XVII. M 
