252 



SCIENCE, 



[Vol. IV., No. 84. 



sometimes happened that each of several quite differ- 

 ent explanations of a phenomenon might be perfectly 

 correct. This proposition came nearer affording a 

 ' substantial basis of agreement' than any thing else; 

 but it cannot be denied that the impression remained 

 on the minds of many in the section, that the extreme 

 views were nearly, if not quite, irreconcilable with 

 each other. Among the interesting results of the 

 discussion was the somewhat unexpected limitation 

 put upon the generally accepted idea of the ' poten- 

 tial of a body,' by Sir William Thomson. This he 

 defined to be the energy expended in bringing unit 

 electricity from an infinite distance to a point in air 

 extremely near the surface of the body. 



Lord Rayleigh described a galvanometer of twenty 

 wires which he had constructed, by joining the wires 

 in multiple arc and also in series, so that the constant 

 of one circuit was exactly ten times that of the other. 

 The instrument was useful for the accurate standard- 

 izing of ammeters for measuring currents of from 

 ten to fifty amperes. Professor Shuster discussed the 

 influence of magnetism on the discharge of electricity 

 through gases. He had found that this influence was 

 very different upon the discharge from large electrodes 

 from those usually observed when small electrodes are 

 used. The construction of an apparatus of peculiar 

 form, with large electrodes, had enabled him to ob- 

 tain many curious effects by the introduction, between 

 the electrodes, of electro-magnets of various forms. 

 He had also found that none of the usual Crooke's 

 effects are produced in mercury-vapor tubes, and this 

 was connected in the theory of the operation with the 

 fact that mercury was a monatomic substance. 



In the discussion of a paper by Lord Rayleigh on 

 telephoning through a cable, Mr. W. H. Preece re- 

 lated his experiences in telephoning the Dublin and 

 Holyhead cable, a distance of sixty miles, which had 

 been fairly successful ; accurately heard conversation, 

 however, could not be carried on beyond a distance 

 of twenty-five miles. Other experiments had proved 

 that it was at present impracticable to use under- 

 ground wires in cities for distances of more than 

 twelve miles. In every experiment telephonic circuits 

 were made metallic. With an arrangement of double 

 lines he said he had no difficulty in speaking through 

 two hundred and forty miles on overground wires. 



The much-talked-of, and one might justly say the 

 much-abused subject, of the connection of sun-spots 

 with terrestrial phenomena, received considerable 

 attention in a discussion which was opened by Prof. 

 A. Schuster. It is generally agreed that sun-spots 

 have a periodicity; the length of their period being 

 somewhat irregular, varying, indeed, from about 

 eight years to fifteen or sixteen years, but the mean 

 from maximum to maximum being about eleven 

 years. This period might be the resultant of several 

 periods superposed; and Professor Balfour Stewart 

 had pointed out the fact that the irregularity observed 

 could be fairly well accounted for by supposing the 

 superposition of two periods of about ten and a half 

 and twelve years respectively. 



The first noticeable effect of this sun-spot cycle 

 was the corresponding cycle in the daily variation 



of the magnetic needle, — a relation which was also 

 generally admitted. From maximum sun-spot area 

 to minimum sun-spot area, the daily variation of the 

 needle changes in the ratio of about three to two; 

 and in at least two instances brief but violent dis- 

 turbances in the sun had been known to be accom- 

 panied, or at least followed closely, by similarly brief 

 but marked disturbances of the magnetic needle. 

 Such was undoubtedly the case in 1859, as observed 

 by Carrington; and again in 1872, as observed by 

 Professor Young. Professor Loomis has shown that 

 there is an intimate relation between the sun-spot 

 cycle and that of the aurora borealis; and, in fact, 

 the practical agreement of those three cycles — the 

 sun-spot, the magnetic, and that of the aurora — 

 may now be considered as universally admitted. 

 But although much time and great labor have been 

 expended in this direction, it must be admitted that 

 no other connection of solar disturbance as shown 

 in sun-spots, with terrestrial phenomena, has been 

 so completely proved as to command general con- 

 fidence. 



The question of accounting for the magnetic in- 

 fluence had been considered. Were the sun made of 

 solid steel, and magnetized to saturation, it could not 

 produce the effects upon the magnetic condition of 

 the earth which are now justly attributed to it. 

 Whether electricity is conducted in some way or other 

 from the sun to the earth, is a question which cannot 

 at present be answered, although it would be rash to 

 affirm that the space between the sun and the earth 

 does not contain enough matter to conduct electricity. 

 It has been suggested, that variations in the amount 

 of heat radiated from the sun might be shown to be 

 an important factor; and some determinations of the 

 total solar radiation have seemed to indicate that the 

 total amount varied from time to time by as much as 

 eight per cent. But the measurement of the sun's 

 radiation is surrounded by the greatest difficulties, 

 on account of the unknown and possibly varying ab- 

 sorption of the earth's atmosphere. Professor Schu- 

 ster was convinced that the only mode of attempting 

 the solution of the problem lay in the direction 

 of evading this disturbance by establishing observing 

 stations on the highest accessible points; and he 

 suggested the Himalaya Mountains as offering, on 

 many accounts, the most suitable locality. As the 

 question now stood, he believed he was correct in 

 saying that we know nothing of the variation of the 

 sun's radiation. 



The question as to the possibility of investigating 

 the problem, through observed temperature effects 

 upon the surface of the earth, had naturally been 

 considered. In spite of the difficulties surrounding 

 the subject, there could be no doubt that several dif- 

 ferent observers had proved that a connection existed 

 between the sun-spot period and certain temperature 

 effects upon the earth. Among these effects may be 

 mentioned the agreement between this period and 

 the best wine years on the Rhine; and also with the 

 period of the increasing and decreasing number of 

 cyclones upon the Indian Ocean. 



As to a similar period in mean atmospheric press- 



