NATURE 



417 



THURSDAY, SEPTEMBER 3, 1891. 



THE REPORT OF THE BOARD OF TRADE 

 COMMITTEE ON ELECTRICAL STANDARDS. 



TARDILY, and in a somewhat piecemeal if not 

 grudging fashion, some small provision has been 

 made by Her Majesty's Government for the regulation, 

 under the Board of Trade, of the new but vigorous and 

 rapidly-extending industry which recent developments of 

 electrical science have brought into existence. In no 

 previously-existing branch of trade has the problem of 

 settling standards of measurement been so difficult of 

 solution, and in no other has the problem been so com- 

 pletely solved without trouble, expense, or intervention 

 on the part of the Government itself. For the last 

 twenty-five or thirty years a Committee of the British 

 Association has laboured at the gigantic task of building 

 up a system of units, which involved as a mere pre- 

 liminary the revision of the conceptions and units of 

 dynamics in order that these might form a basis for the 

 definition of units for thefar more complex physical quanti- 

 ties concerned in electricity and magnetism, quantities 

 many of which had previously been by no means clearly 

 apprehended, and which then received for the first time 

 precise statement and definition. 



Much of the work of the British Association Commit- 

 tee has been thankless, tedious, and, from its very nature, 

 of a kind fitted to excite the cheap scorn of the self-styled 

 " practical man," but it has made applied electricity 

 possible, and has reacted in no slight degree on the pro- 

 gress of theory itself. The problem of the determination 

 of the ohin — in other words, the process of realizing a 

 standard of resistance according to the theoretical defini- 

 tion — has suggested problems to the theorist in the solu- 

 tion of which the theoretical investigator has been led to 

 both direct and side-results of the very greatest value to 

 the progress of science, and, in an unexpected manner, to 

 the facilitation of practical applications. In no science 

 have theory and practice been so closely connected during 

 the last quarter of a century, and in none has the union 

 been so markedly productive of good. By far the most 

 interesting chapters of the history of electricity during 

 the nineteenth century will be those that refer to its 

 last three decades ; may they chronicle a still closer 

 alliance of the engineer and the experimenter, the elec- 

 trical man of action and the mathematician ! Here union 

 is strength and dominion over the forces of Nature ; dis- 

 union is waste of energy and slow progress in all that 

 relates to the material, and therefore also to the social, 

 advancement of the human race by means of electrical 

 invention. 



The establishment of the nucleus of an electrical 

 standardizing laboratory in London, and the appoint- 

 ment towards the end of last year of a Committee to 

 decide upon and recommend for adoption electrical 

 standards for use in trade, testify to the great import- 

 ance which the electrical industries have attained in this 

 country in spite of the mistakes which attended their in- 

 ception, and the general discouragement and disfavour 

 with which they were received by the various interests 

 they threatened. 



NO. I 140, VOL. 44] 



The proceedings and report of the Committee have 

 just been published in a blue-book, which contains matter 

 of great interest to all engaged in electrical work. The 

 vista which it opens up as regards the future operations 

 of the standardizing laboratory may well dismay Her 

 Majesty's Government ; although no doubt due provision 

 will ultimately be made for all its work. But of this at 

 another time ; at present we wish to direct attention to 

 the resolutions of the Committee, which will be found in 

 another page. 



In the first place the Committee signify their ad- 

 herence to the units of length, mass, and time as funda- 

 mental units, and adopt the C.G.S. system. This was 

 only to be expected, for, after all, though some people 

 may think that a better system could be devised if the 

 work had to be done afresh, and they had a share in it, 

 still collectively the body of scientific opinion is distinctly 

 conservative, and there is little danger that any ill-advised 

 attempt to disarrange the accepted system of theoretical 

 and practical units will succeed. 



Their third resolution, that the standard of electrical 

 resistance should be called the ohm and should have the 

 value I 000,000,000 in terms of the centimetre and second 

 in the ordinary electromagnetic system, is of great im- 

 portance. It seems to settle once for all the question 

 which has been debated over and over again, whether 

 after a standard ohm has been realized, it will, like the 

 standard yard or metre, be ever after the standard ; or 

 whether, if in case of variations in the physical properties 

 of the substance, it shows an unexpectedly large diver- 

 gence from the definition, a new standard ought to be 

 constructed. Those who have assumed the former al- 

 ternative have forgotten that the ohm is a derived unit, 

 depending on the already fixed units of length, mass, and 

 time, and that, therefore, its derivation ought to be as 

 exact as the ever-widening resources of science can make 

 it. For practical purposes of trade the standard fixed 

 upon now and its copies are likely to remain undisturbed 

 for a long time, and will probably only be corrected if 

 there is serious alteration with time in their resistances. 

 But the ohm will still be defined as 10^ C.G.S. in the 

 ordinary electromagnetic system of measurement, in 

 which the magnetic permeability of air is assumed to be 

 unity. 



The fourth and fifth resolutions provide the definition 

 of a practical realized ohm (i) by means of a column of 

 mercury, (2) by comparison with the British Association 

 unit, which it is stated may be taken as -9866 of the 

 ohm. 



The wording of Resolution 4 strikes one as curious. 

 The mercury column is to have a "constant cross-sec- 

 tional area of I square millimetre." If " constant" has 

 its ordinary sense of invariableness with time, the specifi- 

 cation of I square millimetre renders it unnecessary. Ft 

 has here apparently the usual sense of " uniform," that is, 

 the section is the same at every part of the tube. 



We are glad to see that the length adopted for the 

 tube is io6'3 centimetres, instead of 106 centimetres, the 

 round number adopted at the Paris Conference, and pro- 

 posed, by the British Association Committee in 1886, to 

 be legalized for a period of ten years. All the latest and 

 best determinations of the ohm point to io6'3 as a con- 

 venient number very closely agreeing with the true value, 



T 



