Description of a Rotatory Multiplier. 



339 



Art. 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. 



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The preceding engraving represents a rotatory galvanometer, 

 or multipHer, 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 



