ADDRESS OF PROF. S. NEWCOMB. 445 



number of experiments illustrative of the theory are described. 

 With a battery having a single plate of zinc, of half a square foot 

 of surface, he made a magnet lift a weight of 750 pounds, more 

 than thirty-five times the weight of the magnet. 



In the same year, J 831, he describes a little machine for produ- 

 cing continuous mechanical motion by magnetic attraction and 

 repulsion. He considered the apparatus to be merely a philosophical 

 toy involving a principle which at some future time might be applied 

 to a useful purpose. 



In 1830, at the request of Professor Ren wick, he commenced a 

 series of observations to determine the magnetic intensity at Albany. 

 This gave him occasion to investigate a subject of which the evi- 

 dences had before been very conflicting, namely, the effect of the 

 aurora upon the magnetism of the earth. 



In 1831, April 19, at 6 P. M., a remarkable phenomenon was 

 noticed, namely, an extraordinary increase in the number of vibra- 

 tions of the needle, and in the consequent magnetic intensity of the 

 earth. Every precaution was taken that no local influence should 

 affect the magnet, but the result was the same. About 9 o'clock in 

 the evening a brilliant aurora commenced. The idea now occurred to 

 him that it might be connected with the magnetic disturbance, and 

 another observation of the magnet was therefore made. The result 

 was the opposite of what had been anticipated, for instead of show- 

 ing a continuous increase the intensity was now far below the aver- 

 age. An extended discussion of other results of the same sort is 

 given, followed by an inquiry into the origin of the aurora. 



The next important investigation in which Professor Henry 

 appears is that which led to his being an independent discoverer of 

 magneto-electricity. In the early experiments in this direction we 

 have an interesting example of how a discovery may be long re- 

 tarded through the want of correct theoretical notions. The idea 



O 



entertained by the early experimenters of the present century seems 

 to have been that since a galvanic current passing around a core of 

 soft iron renders it magnetic, it may be expected that a magnet placed 

 inside of a coil of wire will cause a current of electricity to pass 

 through it. Accordingly, endeavors were made to produce this 

 current by using powerful magnets. But since a continuous gal- 



