102 WRITINGS OF JOSEPH HENRY. [1837 



wire contains its natural quantity, the whole spark is thrown 

 ofif in the form of a lateral discharge. But to explain these 

 phenomena more fully, Professor Henry remarked that it 

 appeared necessary to add an additional postulate to our 

 theory of the principle of electricity, namely, a kind of mo- 

 mentum, or inertia without weight. By this he would only 

 be understood to express the classification or generalization 

 of a number of facts which would otherwise be insulated. 

 To illustrate this, he stated that the same quantity of elec- 

 tricity could be made to remain on the wire if gradually 

 communicated ; but when thrown on in the form of a spark 

 it is dissipated, as before described. Other facts of the same 

 kind were mentioned ; and also that we could take advantage 

 of the principle to procure a greater effect in the decompo- 

 sition of water by ordinary electricity. The fact of a wire 

 becoming luminous by a spark was noticed by the celebrated 

 Van Marum more than fifty years ago; but he ascribed it to 

 the immense power of the great Haarlem machine. The 

 effect however can be produced, as before described, by a 

 cylinder of Nairn's construction of seven inches in diameter, 

 a globe of a foot in diameter being placed in connection 

 with the prime conductor to increase its capacity. 



Some experiments were next described in reference to the 



CI induction of the lateral action of different dis- 

 . charges on each other. When the long wire is 

 arranged in two parallel but continuous lines 



(I by bending the wire the outer side of each wire 

 only becomes luminous. When formed into 

 A three parallel lines by a double bend the middle 

 I • portion of the wire does not become luminous, 



the outer sides only of the outer lines of wire exhibit the 

 rays. When the wire is formed into a flat spiral the outer 

 spiral alone exhibits the lateral discharge, but the light in 

 this case is very brilliant ; the inner spirals appear to in- 

 crease the effect by induction. 



Professor Henry stated that a metallic conductor inti- 

 mately connected with the earth at one end, does not silently 

 conduct the electricity thrown in sparks on the other end. 



