314 



SCIENCE 



[Vol. IV., No. 86. 



Sir William Thomson then made a short address, 

 after which the conference adjourned to meet on 

 Tuesday, when the regular discussions were begun. 



The object of the conference was to take authorita- 

 tive action respecting the electrical standards recom- 

 mended by the international convention; to consider 

 the advisability of recommending the establishment 

 by the government of a bureau of physical standards ; 

 to consider what could be done by the U. S. signal- 

 service, with the co-operation of the various telegraph 

 and telephone companies, towards increasing our 

 knowledge, of atmospheric electricity and earth-cur- 

 rents ; and to discuss subjects in which the knowledge 

 possessed by those acquainted with the theory of 

 electricity could be brought to the aid of those en- 

 gaged in the applications of the science. The senti- 

 ment of the conference was in favor of adopting the 

 electrical standards recommended by the interna- 

 tional convention which met at Paris last April; but, 

 as considerable difference of opinion exists as to the 

 best standard of light to be adopted, the whole sub- 

 ject of the electrical standards was referred to a com- 

 mittee which is to report to the commission within 

 three months. In the discussion of the adoption of 

 the legal ohm, as denned by the Paris convention as 

 the resistance of a column of pure mercury at zero 

 degrees centigrade, of one square millimetre cross- 

 section and one hundred and six centimetres in 

 length, it was brought out that the results obtained 

 in the experiments which have been carried on du- 

 ring the past year under Professor Rowland's direc- 

 tion, give very nearly 106.28 centimetres as the length 

 of the column of mercury which represents the true 

 ohm. 



The subject of the best methods of extending our 

 knowledge of atmospheric electricity and earth-cur- 

 rents, and any possible relation that may exist between 

 them and the weather, was introduced by Professor 

 Abbe of the signal-service. He represented the im- 

 portance of the subject, and that by using suitable 

 methods, and by the co-operation of the various tele- 

 phone and telegraph companies, much valuable in- 

 formation might be obtained, and without interfering 

 with the regular work of the lines employed. Sir 

 William Thomson called attention to the fact, that in 

 the study of earth-currents the quantity to be meas- 

 ured is the difference of potential between the points 

 of observation. By such measurements the distri- 

 bution of potential at any time over the country exam- 

 ined may be mapped and studied. 



The question of the establishment of a bureau of 

 physical standards was introduced by Professor Snyder, 

 who pointed out the advantages which would result 

 from having physical standards preserved and verified 

 under government supervision. Work which is now 

 being done by different observers all over the country, 

 and in a way which is often necessarily incomplete 

 from the lack of funds, could thus be done at a 

 central laboratory, more cheaply, effectively, and accu- 

 rately; and thus the physicists now engaged in these 

 laborious determinations and comparisons would be 

 free to occupy themselves with investigations looking 

 to the discovery of new truth. In the discussion 



which followed, Professor Rogers of Cambridge, 

 Mass., urged that the bureau should engage in auxil- 

 iary research, and showed how this was necessary for 

 the accurate establishment of units. Lieut. Allen of 

 the signal-service read a paper giving an account of the 

 success that had attended the work of that depart- 

 ment in obtaining accurate standards for thermome- 

 try and barometry. Professor Hilgard, superintendent 

 of the U. S. coast-survey, was not in favor of such a 

 bureau, on the ground that it would discourage pri- 

 vate research, and that the present bureau of weights 

 and measures met every requirement. Professor 

 Simon Newcomb spoke in favor of the proposed bu- 

 reau; and Sir William Thomson not only favored the 

 idea, but thought that instruments of the accuracy 

 required by such a bureau for its work would soon 

 be devised and constructed, and the time was there- 

 fore ripe for such action to be taken. Finally the 

 conference adopted a resolution to the effect that it ■ 

 deemed it of national importance that Congress should 

 fix standards of electrical measures, and establish a 

 bureau charged with the duty of examining and veri- 

 fying instruments for electrical and other physical 

 measurements. The commission was urged to bring 

 the matter before congress ; and it was left with them 

 to decide upon the manner of the carrying-out of the 

 idea, whether by a special bureau, or by enlarging 

 the powers and duties of existing departments. 



Among the discussions that occupied the attention 

 of the conference, perhaps the mOst interesting one 

 was that opened by Prof. Henry A. Rowland, upon 

 the theory of the dynamo-electric machine. Professor 

 Rowland maintained, that, neglecting the question 

 of strength and rigidity and other such mechanical 

 reasons, a single magnetic circuit is better than a 

 double one: meaning, by a single magnetic circuit, 

 such a one as would be obtained by placing the 

 armature between the poles of an ordinary horse- 

 shoe magnet; and by a double magnetic circuit, one of 

 the form obtained by putting two horseshoe magnets 

 end to end with their similar poles together, and put- 

 ting the armature between the compound north and 

 south poles thus formed. In the single circuit the 

 lines of force, after passing through the armature, can 

 only return in one way through the magnet; in the 

 double circuit, however, the lines of force can return 

 by passing around either through one magnet or the 

 other. Professor Rowland is of the opinion that there 

 is far more leakage of the lines of force in the case 

 of the double circuit than in the case of the single ; 

 and therefore, other things being equal, the single 

 circuit is the better form. This is, however, a ques- 

 tion that should be investigated by experiment. Both 

 forms of dynamo should be carefully examined to 

 determine the amount of leakage at every point. 

 Such an investigation would be very important. 

 Professor Rowland also advocated the use of magnets 

 of cylindrical section, rather than flat or oval magnets, 

 on the ground that the least amount of wire would 

 then be used to produce the required magnetization of 

 a given mass of iron. Professor Silvanus P. Thomson 

 differed on this point, and preferred iron cores of 

 oval section; giving as his reason, that he had found 



