Description of a Rotatory Multiplier. 339 
Arr. XIX.—Engraving and Description of a Rotatory Multi- 
plier, or one in which one or more Needles are made to revolve 
by a Galvanic Current ; by R. Hare, M. D., Prof. of Chem. 
in the Univ. of Penn. Read before the Amer. Philos. Society, 
Dec. 7, 1838: 
Bee 
Tue preceding engraving represents a rotatory galvanometer, 
or multiplier, which I contrived in November, 1836, and which 
must have value as an addition to the amusing, if not to the useful 
implements of science. It is well known that by passing a tem- 
porary discharge through the coil of a multiplier, the needle may 
be made to perform a revolution, whereas if the current be con- 
tinuously applied, the movement is checked as soon as the situa- 
tion of the poles is reversed. ‘To produce a permanent motion, 
the discharge must be allowed to take place only when the poles 
are in-a favorable position, relatively to the excited coil. This 
object I attained by means of two pins, descending from the nee- 
dle perpendicularly, so as to enter two globules of mercury, com- 
municating, on one side, with a galvanic pair, on the other with 
the coil of the multiplier. In the next place, by winding over the 
first coil, another of similar length, but in a direction the opposite 
of that in which the first coil was wound, I was enabled, by two 
other globules, situated so as to communicate severally with the 
lower ends of the pins, at the opposite side from that on which the 
first mentioned globules were, to cause an impulse at every semi- 
revolution. : . 
The one coil being wound to the right, the other to the left, 
the alternate effect of each upon the needle was similar in opposite 
