Dr. Hare's Electrical Machine, &fc. 279 



live than it is positive, nor more positive than it is negative. Hence 

 I do not approve of another suggestion of the same author, that the 

 diminution of light near the middle of the spark resuhs from the 

 combination of the different fluids at this point. It appears to me 

 that there is as httle ground for supposing the union of the fluids to 

 take place there as elsewhere. But admitting that the union does 

 take place as supposed, is this a reason for the observed diminution of 

 light ? If, v^rhen isolated, either fluid is capable of emitting a brill- 

 iant light, should not their co-operation increase the effect? If, 

 after their union, they do not shine, it can only be in consequence 

 of their abandoning, at that moment, all the light with which they 

 were previously associated. It cannot be imagined that the light 

 accompanying one should neutralize that accompanying the other. 



In deflagrating, by voltaic electricity, a wire of uniform thickness, 

 equally refrigerated, the most intense evolution of heat and light is 

 always midway. 



In truth, the theory which the learned author sanctions, requires 

 two postulates so irreconcilable, that unless one be kept out of view, 

 the other cannot be sustained. It requires that the fluids should 

 exercise an intense reciprocal attraction, adequate to produce chem- 

 ical affinity, and of course, enter into combination when they meet, 

 and yet rush by each other with inconceivable velocity, not only 

 through the air, but also through the restricted channel afforded by 

 a small wire. If the fluids combine at a point intervening between 

 the surfaces from which they proceed, what becomes of the com 

 pound which they form ? Is it credible that such a compound would 

 afford no indication of its existence ? But, again, how are two sur- 

 faces, the one previously deprived of a large portion of the negative 

 electricity naturally due to it, the other made as deficient of the posi- 

 tive fluid, to regain their natural state ? By a combination midway, 

 the resinous and vitreous surcharges might be disposed of, but whence 

 could the vitreous and resinous deficiencies be supplied ? 



Dr. Thomson, in common with the great majority of modern chem- 

 ists, ascribes chemical affinity to the attraction between the two elec- 

 tricities combined with ponderable particles. As the combinations 

 between such particles take place only in definite proportions, would 

 it not be consistent that the fluids which give rise to them, should 

 combine agreeably to those laws ? But if the electrical compound, 

 formed of the vitreous and resinous electricities, be decomposable by 

 induction, as the theory in question requires, its constituents must be 

 capable of uniting in every proportion. 



