214 MEMORIAL OF JOSEPH HENBY. 



produced the first efficient electro-magnet; — capable of sustaining 

 several pounds by its armature, when duly excited by the galvanic 

 current. He had also greatly improved lecture-roora apparatus for 

 illustrating the electro-magnetic reactions of rotations, etc. (where 

 a permanent magnet is employed), by introducing stronger magnets, 

 and had thereby succeeded in exhibiting the phenomena on a larger 

 scale, with a considerable reduction of the battery power. * 



Faraday had not yet commenced the series of researches which 

 in after years so illumined his name, when Henry published his first 

 contribution to electrical science, in a communiciition read before the 

 Albany Institute, October 10th, 1827, "On some Modifications of 

 the Electro-Magnetic Apparatus." From his experimental investi- 

 gations he was enabled to exhibit all the class illustrations attempted 

 by Sturgeon, on even a still larger and more conspicuous scale,, 

 with the employment of very weak magnets (where required), and 

 with a still further reduction of the battery power. These quite 

 striking and unexpected results were obtained by the simjjle expe- 

 dient of adopting in every case where single circuits had previously 

 been used, the manifold coil of fine wire which Schweigger had 

 employed to increase the sensibility of the galvanometer. He 

 remarks : 



" Mr. Sturgeon of Woolwich, who has been perhaps the most 

 successful in these improvements, has shown that a strong galvanic 

 power is not essentially necessary even to exhibit the experiments 

 on the largest scale. - - - ]\Ir. Sturgeon's suite of apparatus, 

 though superior to any other as far as it goes, does not however 

 form a complete set: as indeed it is plain that his principle of 

 strong magnets cannot be introduced into every article required,, 

 and particularly into those intended to exhibit the action of the 

 earth's magnetism on a galvanic current, or the operation of two 

 conjunctive wires on each other. To form therefore a set of instru- 

 ments on a large scale that will illustrate all the facts belonging to 



* Trans. Soc. Encouragement Arts, etc. 1825, vol. xHli. pp. 38-62. His battery (of & 

 single element) consisted "of two fixed hollow concentric cylinders of thin copper, 

 having a movable cylinder of zinc placed between them. Its superficial area is only 

 130 square inches, and it weiglis no more than 1 lb. 5 ozs." Mr. Stukqeon was de- 

 servedly awarded the Silver Medal of the Society for the Encouragement of Arts, 

 etc., "for his improved electro-magnetic apparatus." Described also in xhmals of 

 I'hilos. Nov. 1820, vol. xli. new series, pp. 357-301. 



