376 MEMORIAL OF JOSEPH HENRY. 



Note B. (From p. 227.) 

 "INTENSITY" AND " QUANTITY" CURRENTS. 



Early in the century, the eminent chemist Dr. Thomas Thomson 

 endeavored to express the difference between mechanical electricity 

 and chemical electricity, by characterizing the former as possessing 

 "intensity," and the latter as possessing "quantity." From the 

 increase of electrical effects with the multiplication of galvanic 

 pairs in a pile or battery, Volta a short time before had designated 

 such action as "electromotor" force. Dr. Robert Hare in 1816 

 devising a galvanic battery in which all the positive elements were 

 directly connected together, as were all the negative elements, (thus 

 constituting it virtually a battery of a single pair,) from the heating 

 effects obtained, designated the action as "calorimotor" force. It 

 appeared quite natural afterward to distinguish these classes of 

 effects by the old terms "intensity" for electromotive force, and 

 "quantity" for calorimotive force. There is obviously a close anal- 

 ogy between these differences of condition or resultant, and the 

 more strongly contrasted conditions of mechanical and chemical 

 electricity : and indeed the whole may be said to lie in a continuous 

 series, from the highest "intensity" with minimum quantity, to the 

 greatest "quantity" with minimum intensity. 



Peltier in 1836 published a paper entitled "Definition of the 

 terms electric Quantity and Intensity, derived from direct experi- 

 ment:" in which he showed that "if we form a voltaic pair of two 

 fine wires, zinc and copper, immersed in pure water, and connected 

 by a circuit of copper wire 300 metres (328 yards) long, although 

 there is as we know a continuous current in this closed circuit, the 

 copper wire if placed immediately over a magnetic needle, will not 

 deflect it from the magnetic meridian. But if the needle be sur- 

 rounded by a "multiplicator" formed of 100 or 200 coils of the 

 long wire, there will be at once a notable deviation; and if the 

 number of coils be increased to 2,000 the deviation may extend to 

 60 degrees." In this experiment, as the primitive current has not 

 been changed, but- a "factitious quantity" only has been produced 

 by conducting it 2,000 times around the magnetic needle, Peltier 

 inferred that it is by the quantity (and by no other modification) 

 that the action has been thus enhanced; and that it is therefore 

 through its quantity that a current acts on the magnetic needle. 



"Taking now a thermo-electric pair, zinc and copper, of five square 

 millimetres, (the 129th part of a square inch,) and heating one of 

 the solderings to 40 degrees, (1 04 F.) we find that with the same 

 closed circuit and multiplicator of 2,000 coils, the needle will not 

 be deflected; the electricity will not pass. But if we retrench 



