30 



GALVANISM. 



they terminate are made to communi- 

 cate with one another by means of a 

 syphon full of water, or even by moist- 

 ened threads. We find, under these 

 circumstances, the whole of the oxygen 

 of the decomposed water transferred to 

 the positive, while the hydrogen is col- 

 lected at the negative wire. Two ques- 

 tions may here be asked : first, in what 

 part of the circuit does the decomposi- 

 tion take place ? secondly, in what mode 

 are the elements of the decomposed par- 

 ticles transferred to such distant points, 

 without any indication being afforded of 

 their movements, which must be exceed- 

 ingly rapid, in order to traverse through 

 so long a space ? The velocity of this 

 transfer would appear to be very consi- 

 derable from the following experiment 

 made by Dr. Roget, in the year 1807. 

 The ends of two platina wires, commu- 

 nicating with the poles of a powerful 

 battery, were introduced into two sepa- 

 rate vessels of water, communicating by 

 means of a long tube, bent into the form 

 of a syphon, and filled with a solution 

 of common salt. The whole length of 

 the fluid part of the circuit between the 

 two wires was 46 inches. Microscopes 

 were applied to the ends of the wires, 

 for the purpose of enabling the observer 

 and an assistant, (who was the late Mr. 

 Sylvester,) to ascertain the precise mo- 

 ment when the gases made their appear- 

 ance at the respective wires. No sen- 

 sible interval of time could be perceived 

 between the appearance of the oxygen 

 gas at the positive, and of the hydrogen 

 gas at the negative wire, when the com- 

 munications with the battery were made. 



(104.) The transfer of material and 

 ponderable substances, such as those 

 which constitute the elements of water, 

 might be expected, even with a moderate 

 velocity, to occasion visible currents in 

 the fluid through which they pass ; for 

 their motion, by whatever force pro- 

 duced, must be accompanied by a certain 

 momentum, sufficient to displace the 

 particles of the fluid through which they 

 pass. Dr. Roget could, however, detect 

 no appearance of current or displace- 

 ment of fluid ; such as would be indi- 

 cated by movements among the minute 

 globules of dust, or other extraneous 

 matters suspended in the water, even 

 with the assistance of the microscope. 

 Mr. Wilkinson and Professor de la Rive, 

 have also arrived at the same conclu- 

 sion, by employing microscopes of high 

 magnifying power. 



(105.) These phenomena of transfer 



have appeared to some so inexplicable, ' 

 upon the commonly received doctrine of 

 the composition of water, that they have 

 had recourse to a new hypothesis in order 

 to solve the difficulty. Professor Ritter 

 was led to consider water as a simple 

 substance, forming oxygen by its com- 

 bination with positive electricity, and 

 hydrogen by its union with negative 

 electricity ; and this theory was adopted 

 by several other philosophers. Monge 

 endeavoured to account for the pheno- 

 mena, by supposing that water formed 

 compounds with excess of oxygen on 

 the one hand, or excess of hydrogen on 

 the other ; which compounds passed in 

 opposite directions between the two 

 wires, each depositing on their arrival 

 the superabundant ingredient. Dr. Bos- 

 tock conceived that the water was de- 

 composed at the positive wire only, 

 where its oxygen was disengaged ; and 

 its hydrogen, uniting with electricity, 

 was carried invisibly along with it to 

 the negative wire, where this union 

 being [dissolved, the electricity passed 

 on through the wire, and the hydrogen 

 appeared in its gaseous form. 



(106.) The following mode of ex- 

 plaining these phenomena was sug- 

 gested by Dr. Roget, in a paper which 

 was read to the Philosophical Society 

 of Manchester, in 1807. 



"We may conceive the agency of 

 electricity to extend throughout the 

 whole of the fluid line connecting the 

 two wires. The hydrogen existing in 

 every particle of water in this line, will, 

 if it possess a positive electrical polarity, 

 according to the hypothesis of Mr. 

 Davy, be repelled by the positive, and 

 attracted by the negative wire. We 

 may consider the row of particles of 

 hydrogen abstractedly from those of 

 oxygen. While the former are moving 

 together, by the agency of thejelectricity, 

 in a direction towards the negative wire, 

 all those particles which have not yet 

 reached that wire, will merely have to 

 pass over in succession from one par- 

 ticle of oxygen to the next, among those 

 of the other row. They will not appear 

 in the form of gas, because the instant 

 each has quitted the particle of oxygen 

 with which it was associated, it meets 

 with another to combine with ; and this 

 process will be continually repeated, 

 until it has arrived at the end of the 

 line, when, finding no oxygen to unite 

 itself with, it will make its appearance 

 in the form of gas. In like manner, the 

 first particle of hydrogen, in the series, 



