84 MEMORIAL OF JOSEPH HENRY. 



exciting current as to convert it into an instrument which, instead 

 of being able to bear a few ounces, or at most a few pounds, was 

 capable of sustaining a load of hundreds of pounds, and which by 

 still later improvements, perfected soon after his removal to Prince- 

 ton, exhibited, under the impulse of but a moderate battery power, 

 the enormous sustaining force of more than three thousand pounds. 



I can well remember the astonishment which was created by the 

 announcement of this result and the delight of those who first wit- 

 nessed it. As might well be imagined, this striking achievement at 

 once drew the attention of the scientific world to the rising American 

 electrician. 



It was not that there was extraordinary merit simply in con- 

 structing an apparatus which would support one thousand pounds 

 instead of ten, in making a colossal magnet, but the result claimed 

 admiration because of the series of thoughtful experiments leading 

 to it and to yet wider applications; experiments involving an inves- 

 tigation of the laws which regulated the relation between the bar 

 of iron, the wire or wires which encircled it, the prolonged con- 

 ductor, and the battery which furnished the power. 



Availing himself of the principle already applied in Schweig- 

 ger's galvanometer, Henry succeeded in multiplying the effect of 

 the current by causing it to revolve in an insulated wire closely 

 wound about the iron core in coils Df many thicknesses ; and with 

 this arrangement he compared the forces developed by currents 

 derived from different galvanic elements and through different 

 lengths of conducting wire, and he soon established the fact that 

 such currents were not of necessity quickly spent, as had been main- 

 tained by Barlow, but that, under proper conditions, they retained 

 an available magnetizing force after having traversed wires of con- 

 sidera'ble length. He showed that for securing this persistence over 

 great distances an intensity-battery was required, while for producing 

 great magnetic power near to the source of the current a large sur- 



