September 12, 1884. 



SCIENCE. 



251 



erenee to the true or rotational north rather than the 

 magnetic north. A method was there presented for 

 so mounting a gyrostat about such vertical axis as 

 to reduce the friction to a minimum. The present 

 paper was concerned principally in the presentation 

 and discussion of another and simpler plan for real- 

 izing the same idea. The plan consisted essentially 

 in suspending a gyrostat, properly constructed, by 

 means of a very long and very fine steel wire attached 

 to a torsion-head, capable of being turned about a 

 vertical axis, at the top. The gyrostat being sus- 

 pended, by successive adjustments of the position of 

 the torsion-head, a position is found in which the po- 

 sition of the gyrostat, in relation to the torsion-head, 

 shows that the wire is free from torsion. In this 

 position the axis of the gyrostat will be in the true 

 north-and-south line; and, if disturbed from this 

 position, it will vibrate about it precisely as does 

 an ordinary magnetic needle about the magnetic 

 meridian. 



The author pointed out several difficulties in the 

 way of the complete realization of the idea, and 

 closed by suggesting some possible methods of 

 mounting, in a simple way, a gyrostat free to move 

 about an axis rigorously or very approximately verti- 

 cal. Eegardless of any practical results which may 

 come from it, the suggestion of a gyrostatic compass 

 is singularly interesting as an example of how motion 

 may effectively take the place of a directing force, 

 although only one of the many which Sir William 

 Thomson has furnished. 



As" was naturally to be expected, topics bearing 

 upon the subject of electricity occupied a good share 

 of the time of the section. Unfortunately one or 

 two papers hearing upon this subject had been as- 

 signed to the chemical section, and were presented 

 contemporaneously with the electrical discussion in 

 section A. The paper by Professor Frankland, on 

 the chemical aspects of the storage of power, was 

 one which many members of section A would have 

 been delighted to hear. While it was being read, 

 however, section A was engaged in an extremely 

 interesting discussion of the question of the seat of 

 the electromotive forces in the voltaic cell, which 

 was opened by Professor Lodge. For the first time 

 in the history of the association, the experiment was 

 attempted, of assigning a definite topic for general 

 discussion; and the success was such as doubtless to 

 lead to a permanent establishment of the custom. 

 The selection of Professor Lodge to open the discus- 

 sion was extremely fortunate. He is not only a 

 ready and clear expounder of his own views, but he 

 was fortunate, as a leader in the discussion, in that 

 those views were not those which are generally 

 accepted as being orthodox. His opening paper was 

 largely historical; in fact, too largely so in the opinion 

 of many of his hearers. He traced the history of 

 the discussion from the time of Volta, declaring that 

 the only really great contributions to our knowledge 

 of the subject were those of Yolta in 1801 and of Sir 

 William Thomson in 1851. Of late years the so- 

 called contact theory had been generally accepted. 

 This theory, as generally understood, Professor Lodge 



could no longer accept. He did not believe that two 

 metals in air or water or dilute acid, but not in con- 

 tact, are practically at the same potential ; or that two 

 metals in contact are at seriously different potentials, 

 or that the contact force between a metal and a dia- 

 lectic, or between a metal and an electrolyte, is 

 small. He did believe that by far the greatest part 

 of the electromotive force of a voltaic cell exists at 

 the zinc and liquid contact rather than at the zinc 

 and copper contact, as generally supposed, although 

 he believed that there was an electromotive force at 

 the junction of every two substances. A summary 

 of the argument may be briefly given as follows, 

 which, as far as it goes, is in Professor Lodge's own 

 words: — 



Wherever a current gains or loses energy, there 

 must be a seat of electromotive force ; and converse- 

 ly, wherever there is a seat of electromotive force, a 

 current must lose or gain energy in passing it. 



A current gains no energy in crossing from copper 

 to zinc, hence there is no appreciable electromotive 

 force there. 



When a current blows from zinc to acid, the energy 

 of the combination which occurs is by no means 

 accounted for by the heat there generated, and the 

 balance is gained by the current; hence at a zinc 

 acid junction there must be a considerable electro- 

 motive force (say, at a maximum, 2.3 volts). 



A piece of zinc immersed in acid is therefore at a 

 lower potential than the acid; though how much 

 lower it is impossible to say, because no actual chem- 

 ical action occurs. 



It was not to be expected that this statement of 

 views, differing so greatly from those usually held, 

 would be received without some protest, and particu- 

 larly from Sir William Thomson, who has been re- 

 garded as the chief exponent and expounder of the 

 metallic-contact theory. Professor Lodge was per- 

 fectly successful in inaugurating a discussion which 

 was full of interest; although it can hardly be said to 

 have contributed much to the discovery of a substan- 

 tial basis of agreement, as he had evidently hoped. 

 Sir William Thomson presented his own views at 

 some length. The subject was one surrounded by 

 great difficulties. He thought there could be no 

 doubt as to a difference of potential at the zinc-copper 

 junction, but the question of the electro-motive force 

 of a voltaic cell might be separated from that of dif- 

 ference of potential at the junctions. He fully agreed 

 with Professor Lodge in his view of the seat of the 

 ' working-force ' in the cell. The ' working-force ' 

 was essentially chemical force. Undoubtedly, in a 

 certain sense, both the chemical and voltaic or con- 

 tact views of the question were correct. 



Professor Kowland, on being called upon to express 

 his opinion, with characteristic frankness declared 

 that he knew nothing about it. Professor Willard 

 Gibbs called attention to the fact that this was a case 

 similar to several other well-known physical problems, 

 in which an attempt to determine the exact point or 

 place at which a force resides had not been rewarded 

 with success. In such cases much depends upon the 

 standpoint from which the subject is viewed, and it 



