Ill MEMORIAL OF JOSEPH HENRY. 



by physical experiments. Bui in the department of electricity, 

 that in which Franklin took so prominent a position, it may be 

 doubted whether they enunciated a single generalization which will 

 enter into the history of the science. This interregnum closes with 



the researches now c< nenced by Professor Henry. His first 



published paper on the subject was read in 1827 before the Albany 

 [nstitute, and is entitled, "On some modifications of the electro- 

 magnetic apparatus." It sisted simply of a brief discussion of 



several forms of apparatus designed to exhibit the mutual action of 

 the galvanic current and the magnet, but does not appear to com- 

 prise any discussions of new ideas. Two years later he published 

 a topographical sketch of the State of New York, which also 

 appeared in the Transactions of the Albany institute. It comprises 

 a brief sketch of the physical geography of the State with especial 

 reference to the newly inaugurated canal system. 



In 1831, he published in Silliman's Journal, a paper on the devel- 

 opment of great magnetic power in soft iron with a small galvanic 

 element. This paper is in some sort a continuation of his first paper, 

 the fundamental object of both being to show how the greatest 

 development of power could be obtained with the smallest battery. 

 The ideas were suggested by the study of Schweigger's Galvan- 

 ometer. He shows that in a piece of soft iron the magnetic power 

 produced by the galvanic current may be greatly increased by 

 increasing the number of coils. A still further improvement i> 

 made when, iu.-icad of passing a single coil between the two poles 

 ol the battery, a number of separate insulated wires are wound 

 around the magnet, so that each shall form an independent connec- 

 tion. He was thus enable.] with a battery of a single pair of small 

 plates ( 1 by <J inches) to form an electro-magnet which would lift 

 a weight of 39 pounds. He also intimates that by winding a 

 separate wire on each inch of the magnet a yet greater effect could 

 be attained. This paper also contains the germ of the theory of 

 electro-magnetic force, and of electrical resistance and quantity, 

 though not developed in any generalized form. He explains that 

 with one very long wire a combination of several plates must be 

 used so as to obtain "projectile force," while when several larger 

 wires are used the battery must consist of a single pair. A srreat 



