THE SMITHSONIAN INSTITUTION. 319 



tlian even nncombined or free oxygen ; hence the hyper-oxidc will 

 polarize the particles of water in such a manner that the hydrogen 

 sides turn towards the hyper-oxide. 

 Other hyper-oxides act in like manner. 



§ 3. Comparison of the Contact tJieov}/ icitli that of Schonhein. — If we 

 compare Schonhein' s theory with the contact theory, we must under- 

 stand that they both run parallel, that the phenomena of the open 

 and closed battery can be ex])lained equally well by both ; for Schim- 

 bein only removes the place of excitation of electricity from the point 

 of contact of the metals to the point of contact between metal and 

 liquid. But Schonbein's theory has a decided advantage in this — that 

 it can determine beforehand in all voltaic combinations, the direction 

 of the current from the chemical relations of the substance forming 

 the battery, while the contact theory is wanting in such a principle. 



That the same metals give a current first in one direction, and then 

 in another, according as one or another liquid is placed betAveen them, 

 is perfectly explicable according to the modified contact theory, from 

 the different electromotive relations of the liquids to the metals. 

 Schonbein's theory not only allows the possibility of a reversal of the 

 current by changing the liquids, but it also tells us in what cases, 

 and why, the currrent is reversed. 



Thus Schonbein's theory always determines a priori from the chem- 

 ical nature of the substances which form the battery, the directions of 

 the current, no matter whether the battery is formed of two metals 

 and a liquid, or of two liquids and a metal; while, on the contrary, the 

 contact theory in many cases is so much at fault that it is unable to 

 determine beforehand the direction of the current from a general 

 principle, and in such cases (e. g. in batteries of water, muriatic 

 acid and gold ; water, sulphurous acid and platinum,) an experiment 

 is required to find the direction of the current. 



From these considerations, one would suppose that there could be 

 no doubt as to which of the two theories should prevail ; whether 

 Schonbein's chemical theory, or the modified contact theory. Yet I 

 cannot decide unconditionally for Schonbein's theory, because it en- 

 tirely ignores a well established fact, the fundamental experiment of 

 Volta, and is unable to give an explanation of it. 



That electricity is generated by different metals coming in contact 

 with each other, is a fact well established by experiments, purposely 

 instituted in various forms, and which cannot be ignored nor set 

 aside by such interpretations of the experiments as the opponents of 

 the contact theory have contrived. 



The name contact electricity is exceedingly unfit, and may have 

 contributed not a little to the confusion of the discussion in question ; 

 properly speaking, all electricity, wherever and however it may appear, 

 is contact electricity ; for, in generating electricity, two different 

 kinds of bodies are necessarily, under all circumstances, brought 

 into contact. In electrical machines, glass and amalgam ; in the vol- 

 taic pile, two metals and a liquid ; in the thermo pile, different metal- 

 lic rods. Wherever heterogeneous substances are brought into contact, 

 a development of electricity takes place, but generally a state of elec- 



