292 



NATURE 



[July 28, 1892 



former by bringing scientific workers together and giving them due 

 opportunity for the interchange of knowledge and opinions. To 

 secure this end, it is important that seci/'onal a.ad intersectional dis- 

 cussions should, in future, become the feature of the meetings, but 

 to be successful these must be conducted with fargreater forethought 

 than heretofore— they must be true discussions and must not 

 consist of a number of short papers written without reference to 

 each other or to any central idea, and there must be no limitation 

 of discussion so long as it is to the point. Probably the best plan 

 will be that sectional committees, specially appointed for the 

 purpose, select subjects, and that on each of these someone open 

 a discussion by means of a carefully-prepared paper, printed and 

 circulated at least a month beforehand, among those likely to take 

 part in the debate. Such discussions should be carefully reported, 

 and the edited report should be subsequently published, those who 

 had taken part in the discussion having full liberty allowed them 

 to give expression to their carefully-considered opinions instead 

 of being required merely to punctuate their sentences in proof. 

 The resolution not to report discussions arrived at last year by 

 the Council is most unfortunate. If it were understood that 

 discussions would be reported, speakers would be far more in- 

 terested, and would take far more pains in preparing to take 

 part in them than has hitherto been the case. It is, I think, 

 unnecessary to dwell on the value of true discussion among 

 workers in different, but cognate, branches of science. 



As regards the public functions of the Association, it is un- 

 questionable that much more might— and should— be done on 

 behalf of those who are interested spectators rather than active 

 workers in science. The evening lectures now delivered are 

 often very brilliant expositions, but, as a rule, they have been 

 "above the heads" of a very large proportion even of the 

 members of the Association who have listened to them. I know 

 many who think with me that a more direct effort should now 

 be made to advance the knowledge of science among the general 

 public at these meetings. 



One great reform which must be carried out is the 

 general curtailment of the expenses of the meetings, which make 

 it impossible for any but the largest and richest towns to receive 

 the Association. The lavish expenditure on the Reception Room 

 which has been so frequently witnessed of late years should be 

 unnecessary. So long as we can come together and can 

 accomplish our object — the advancement of science — we should 

 be satisfied with the most modest accommodation and should 

 even be prepared to submit to some privation. At the German 

 Naturforscher Versammlungen the vast majority cater for them- 

 selves, and private hospitality is almost unknown, the social 

 demon, which is so ruthless a destroyer of much of the effective- 

 ness of the B.A. meetings, being kept entirely in the back- 

 ground ; and yet, in my opinion, these meetings are at least 

 as enjoyable and fruitful of result as our own B.A. meetings. 



Then we want younger presidents, on the average — men who 

 are in their prime as'scientific workers. 



Of late years our Council has been far too cautious and con- 

 servative a body, and a large infusion of a liberal and progressive 

 element is necessary if we are to set our house in order, so that 

 it may suit the times. Many of us think that the Council is not 

 in touch with us as a body — somehow we know of its existence, 

 but its functions are mystic and akin rather to those of the 

 Archives of the Royal Society than to those of an energizing 

 and propulsive organ. In these democratic days, it would be 

 well if each section were to return a member to Council. 



Henry E. Armstrong. 



The Position of 47r in Electromagnetic Units. 



There is, I believe, a growing body of opinion that the 

 present system of electric and magnetic units is inconvenient in 

 practice, by reason of the occurrence of 4ir as a factor in the 

 specification of quantities which have no obvious relation with 

 circles or spheres. 



It is felt that the number of lines from a pole should be m 

 rather than the present 4tw, that " ampere turns " is better than 

 4ir«C, that the electromotive intensity outside a charged body 

 might be a instead of \Tca, and similar changes of that sort ; see, 

 for instance, Mr. Williams's recent paper to the Physical 

 Society, 



Mr. Heaviside, in his articles in the Electrician and elsewhere, 

 has strongly emphasized the importance of the change and the 

 simplification that can thereby be made. 



NO. II 87, VOL. 46] 



In theoretical investigations there seems some probability 

 that the simplified formulae may come to be adopted— 



/x being written instead of 47r/i, and /^instead of „ ; 



but the question is whether it is or is not too late to incorporate 

 the practical outcome of such a change into the units employed 

 by electrical engineers. 



For myself I am impressed with the extreme difficulty of now 

 making any change in the ohm, the volt, &c., even though it be 

 only a numerical change ; but in order to find out what practical 

 proposal the supporters of t]je redistribution of 4ir had in their 

 mind, I wrote to Mr. Heaviside to inquire. His reply I 

 enclose ; and would merely say further that in all probability 

 the general question of units will come up at Edinburgh for 

 discussion. Oliver J. Lodge. 



Paignton, Devon, Jtdy i8, 1892. 

 My dear Lodge, — I am glad to hear that the question of 

 rational electrical units will be noticed at Edinburgh — if not 

 thoroughly discussed. It is, in my opinion, a very important 

 question, which must, sooner or later, come to a head and 

 lead to a thoroughgoing reform. Electricity is becoming not 

 only a master science, but also a very practical science. Its 

 units should therefore be settled upon a sound and philo- 

 sophical basis. I do not refer to practical details, which may 

 be varied from time to time (Acts of Parliament notwithstand- 

 ing), but to the fundamental principles concerned. 



If we were to define the unit area to be the area of a circle 

 of unit diameter, or the unit volume to be the volunae of a 

 sphere of unit diameter, we could, on such a basis, construct a 

 consistent system of units. But the area of a rectangle or the 

 volume of a parallelepiped would involve the quantity ir, and 

 various derived formulae would possess the same peculiarity. No 

 one would deny that such a system was an absurdly irrational 

 one. 



I maintain that the system of electrical units in present use is 

 founded upon a similar irrationality, which pervades it from top 

 to bottom. How this has happened, and how to cure the evil, 

 I have considered in my papers — first in 1882-83, when, how- 

 ever, I thought it was hopeless to expect a thorough reform ; 

 and again in 1891, when I have, in my "Electromagnetic 

 Theory," adopted rational units from the beginning, pointing 

 out their connection with the common irrational units sepa- 

 rately, after giving a general outline of electrical theory in terms 

 of the rational. 



Now, presuming provisionally that the first and second 

 stages to Salvation (the Awakening and Repentance) have been 

 safely passed through, which is, however, not at all certain at 

 the present time, the question arises. How proceed to the third 

 stage. Reformation? Theoretically this is quite easy, as it 

 merely means working with rational formula instead of irra- 

 tional ; and theoretical papers and treatises may, with great 

 advantage, be done in rational formula at once, and irrespective 

 of the reform of the practical units. But taking a far-sighted 

 view of the matter, it is, I think, very desirable that the practi- 

 cal units themselves should be rationalized as speedily as may 

 be. This must involve some temporary inconvenience, the 

 prospect of which, unfortunately, is an encouragement to shirk 

 a duty ; as is, likewise, the common feeling of respect for the 

 labours of our predecessors. But the duty we owe to our 

 followers, to lighten their labours permanently, should be para- 

 mount. This is the main reason why I attach so much im- 

 portance to the matter ; it is not merely one of abstract scientific 

 interest, but of practical and enduring significance; for the 

 evils of the present system will, if it continue, go on multiplying 

 with every advance in the science and its applications. 



Apart from the size of the units of length, mass, and time, 

 and of the dimensions of the electrical quantities, we have the 

 following relations between the rational and irrational units of 

 voltage V, electric current C, resistance R, inductance L, per- 

 mittance S, electric charge Q, electric force E, magnetic force 

 H, induction B. Let x^ stand for 4ir, and let the suffixes r and f 

 mean rational and irrational (or ordinary). Also let the pre- 

 sence of square brackets signify that the "absolute" unit is 

 referred to. Then we have — 



_ [Er] _ [V^ = [jy :::: [?r3 - [C^l - [Q<1 . 

 "" ~ W] ~ [Vi] [Hi] [Bi] [C] LQrJ • 



o_[R4= [Lr] ^JS^ 



~ [K,] [L,] [S.] 



