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current which flows through any circuit depends directly upon the 
electromotive forces contained in the circuit and inversely upon 
the resistances of the circuit. Evidently, therefore, when a con- 
siderable resistance is to be overcome, as when a long, fine wire is 
in circuit, the current necessary to fuse this wire, for example, can 
be secured only by increasing proportionately the electromotive 
force, z. e., by increasing the number of pairs in series in the bat- 
tery. While, when the external resistance is small, as is the case 
when a large metallic wire joins the terminals, very little electro- 
motive force, and therefore only a few pairs, is required ; but by 
making the plates large the resistance of the battery is diminished, 
and so the current in the entire circuit is increased. In the defla- 
grator then, the result was attained by increasing the number of 
the plates in order to secure a high electromotive force. In the 
calorimotor the size was increased in order to decrease the total re- 
sistance and so to increase the current. Again, the law of Joule 
gives us the relation between the amount of current flowing through 
a circuit and the development of heat in it ; asserting that the heat 
thus developed is directly proportional to the resistance in the cir- 
cuit and to the square of the current. Consequently the heating 
effects of Dr. Hare’s calorimotor are due to the large current which 
it was the object of its construction to produce. While in the 
deflagrator, although the current is less, and therefore the total 
heating effect is less also, yet the current is urged by a greater pres- 
sure and hence exerts a greater disruptive effect. Another point 
should be noted in connection with these distinctions thus empha- 
sized in Dr. Hare’s generators. Electrical energy may be repre- 
sented by the product of the current and the electromotive force. 
To transmit a given amount of this energy to a distance, either a 
strong current having a low electromotive force may be employed, or 
a weak current having a high electromotive force, provided the pro- 
duct be the same in both cases. But by the law of Joule, the en- 
ergy dissipated as heat, being proportional to the square of the 
current, would entail a serious lossin the former case. Hence the 
economical transmission of electrical energy requires the use of 
generators developing a high electromotive force. 
Joseph Henry became a member of the American Philosophical 
Society in 1835, although it was ten years earlier than this that he 
began his electrical researches at the Albany Academy. Oersted, 
