128 



NA TURE 



[December 8, 1892 



June 7 of this year. Weather and locality have been against my 

 seeing clear sunsets until to-day, when no unusual effects were 

 noticeable ; but Mr. Bishop's letter makes it possible that in 

 other places similar effects may be observable. 



Grenville a. J. Cole. 

 Royal College of Science for Ireland, Dublin, December 4. 



ELECTRICAL STANDARDS. 



THE following supplementary report has been pre- 

 sented to the President of the Board of Trade by 

 the Electrical Standards Committee :— 



To the Right Hon. A. J. Mundella, M.P., President of 

 the Board of Trade. 



Subsequently to the presentation of our former report 

 to Sir Michael Hicks-Beach in July, 1891, we were in- 

 formed that it was probable that the German Government 

 would shortly take steps to establish legal standards for 

 use in connection with electrical supply, and that, with a 

 view to secure complete agreement between the proposed 

 standards in Germany and England, the Director of the 

 Pbysico-Technical Imperial Institute at Berlin, Prof, von 

 Helmholtz, with certain of his assistants, proposed to 

 visit England for the purpose of making exact com- 

 parisons between the units in use in the iwo countries, 

 and of attending the meeting of the British Association 

 which was to take place in August in Edinburgh. 



Having regard to the importance of this communica- 

 tion, it appeared desirable that the Board of Trade should 

 postpone the action recommended in our previous report 

 until after Prof. Helmholtz's visit. 



That visit took place early in August, and there was a 

 very full discussion of the whole subject at the meeting 

 of the British Asso:iation in Edinburgh, at which several 

 of our number were present. The meeting was also 

 attended by Dr. Guillaume, of the Bureau International 

 des Poids et Mesures, and Prof. Carhart, of the Uni- 

 versity of Michigan, U.S.A., who were well qualified by 

 their scientific attainments to represent the opinion of 

 their respective countries. 



It appeared from the discussion that a few compara- 

 tively slight modifications of the resolutions included in 

 our previous report would tend to secure international 

 agreement. 



An extract from the report of the Electrical Standards 

 Committee of the British Association, embodying the 

 results of this discussion, was communicated to us by the 

 Secretary, and willbefoundjin the appendix to this report. 



Having carefully reconsidered the whole question in 

 view of this communication, and having received the 

 report of the sub-committee mentioned in resolution 14 

 of our previous report, we now desire, for the resolutions 

 contained in that report, to substitute the following :— 



RESOLUTIONS. 



(1) That it is desirable that new denominations of 

 standards for the measurement of electricity should be 

 made and approved by Her Majesty in Council as Board 

 of Trade standards. 



(2) That the magnitudes of these standards should be 

 determined on the electro-magnetic system of measure- 

 ment with reference to the centimentre as unit of length, 

 the gramme as unit of mass, and the second as unit of 

 time, and that by the terms centimetre and gramme are 

 meant the standards of those denominations deposited 

 with the Board of Trade. 



(3) That the standard of electrical resistance should 

 be denominated the ohm, and should have the value 

 1,000,000,000 in terms of the centimetre and second. 



(4) That the resistance offered to an unvarying electric 

 current by a column of mercury at the temperature of 

 melting ice I4'452i grammes in mass of a constant cross 

 sectional area, and of a length of io6'3 centimetres may 

 be adopted as one ohm. 



NO. 1206, VOL. 47] 



(5) That a material standard, constructed in solid 

 metal, should be adopted as the standard ohm, and 

 should from time to time be verified by comparison with 

 a column of mercury of known dimensions, 



(6) That for the purpose of replacing the standard, if 

 lost, destroyed, or damaged, and for ordinary use, a 

 limited number of copies should be constructed which 

 should be periodically compared with the standard ohm. 



(7) That resistances constructed in solid metal should 

 be adopted as Board of Trade standards for multiples 

 and submultiples of the ohm. 



(8) That the value of the standard of resistance con- 

 structed by a Committee of the British Association for 

 the Advancement of Science in the years 1863 and 1864, 

 and known as the British Association unit, may be taken 

 as "9866 of the ohm. 



(9) That the standard of electrical current should be 

 denominated the ampere, and should have the value one- 

 tenth (o'l) in terms of the centimetre, gramme, and 

 second. 



(10) That an unvarying current which, when passed 

 through a solution of nitrate of silver in water, in accord- 

 ance with the specification attached to this report, deposits 

 silver at the rate of o-ooiii8 of a gramme per second 

 may be taken as a current of one ampere, 



(11) That an alternating current of one ampere shall 

 mean a current such that the square root of the time- 

 average of the square of its strength at each instant in 

 amperes is unity. 



(12) That instruments constructed on the principle of 

 the balance, in which, by the proper disposition of the 

 conductors, forces of attraction and repulsion are pro- 

 duced, which depend upon the amount of current passing, 

 and are balanced by known weights, should be adopted 

 as the Board of Trade standards for the measurement of 

 current whether unvarying or alternating. 



(13) That the standard of electrical pressure should 

 be denominated the volt, being the pressure which, if 

 steadily applied to a conductor whose resistance is one 

 ohm, will produce a current of one ampere. 



(14) That the electrical pressure at a temperature of 

 15'^ centigrade between the poles or electrodes of the 

 voltaic cell known as Clark's cell, prepared in accordance 

 with the specification attached to this report, may be 

 taken as not differing from a pressure of 1-434 volts, by 

 more than one part in 1000. 



(15) That an alternating pressure of one volt shall 

 mean a pressure such that the square root of the time- 

 average of the squar.e of its value at each instant in volts 

 is unity. 



(16) That instruments constructed on the principle of 

 Lord Kelvin's quadrant electrometer used idiostatically, 

 and, for high-pressures, instrument on the principle of 

 the balance, electrostatic forces being balanced against 

 a known weight, should be adopted as Board of Trade 

 standards for the measurement of pressure, whether un- 

 varying or alternating. 



COURTENAY BOYLE. G, CaREY FOSTER. 



Kelvin. R. T. Glazebrook. 



P. CARDEW, J. HOPKINSON, 



W, H, Preece. W. E. Ayrton. 



Rayleigh. 



T. W. P. Blomefield, Secretary. 

 November 29. 



ON THE PHYSIOLOGY OF GRAFTING.^ 



'PHE volume before us contains the record of several 



i years of research upon the effects of different forms 



of grafts (using the term in its widest significance) in the 



vegetable kingdom. 



I " Ueber Transplantation am Pflanzenkorper. Untersuchunge n zur 

 Physiologie iind Pathologic " Von Dr. Hermann Vochting. Mit 11 Litho- 

 graphierten Tafeln und 14 Figuren im Texte. (Tubingen : Laupp. 1892.) 



