June i6, 1904] 



NA TURE 



16: 



It is to be hoped that the new code for the regulation of 

 public elementary schools recently issued by the Board of 

 Education, containing as it does a much broader and more 

 scientifically planned curriculum, will remedy this defect, 

 which has for many years hampered technical education in 

 this country. It should be added that the report contains 

 the inaugural address to the students of the Central 

 Technical College, by Sir Guilford Molesworth, and also 

 the address of Sir William White at the distribution of 

 diplomas, &c., to the students of the institute's colleges and 

 schools. 



\ CONFERENCE of headmastcrs and headmistresses, of 

 representatives of midland educational authorities, and 

 others interested in secondary education was held on March 

 19 last under the auspices of the University of Birmingham 

 and the City of Birmingham Education Committee. The 

 speeches delivered on this occasion have now been published 

 in pamphlet form. The conference discussed two subjects 

 at separate sessions. At the first meeting attention was 

 directed to the training of secondary teachers — to what 

 extent it is to be carried out (a) in training colleges, (b) 

 in the schools themselves, and how far such training must 

 depend on Government aid. The subject for the second 

 session was the relative weight to be given to the humanities 

 and to science in the various stages of secondary education. 

 The remarks of some speakers in the discussion on the 

 training of teachers for secondary schools showed that the 

 belief in the necessity for training is not yet universal, 

 though much more common than a few years ago. The 

 headmaster of Shrewsbury, criticising the oft-repeated con- 

 tention that the chief business of the secondary school is 

 to train character, appropriately said : — " Is the day-school 

 teacher — the secondary school teacher, I mean — to devote 

 himself wholly to the formation of character, while at the 

 same time England is falling into the rear in the matter 

 of commerce and in scientific methods? We may con- 

 centrate our efforts on the formation of character until we 

 forget how much more we have to do." The discussion on 

 the relative importance of the humanities and of science was 

 instructive as demonstrating the wide divergence of opinion 

 which exists on most educational problems. Men of science 

 will be disposed to agree with Sir Oliver Lodge, who 

 said : — " I uo not much care what is taught so long as it 

 is taught well, and so long as the pupils learn what is 

 taught. ... I do not believe in having schools where boys 

 having an aptitude for science shall learn nothing else, and 

 schools where boys who have an aptitude for letters shall 

 have nothing but a literary education." A complete educa- 

 tion recognises the claims both of scientific and literary 

 studies, and gives to each of these branches of knowledge 

 its proper place. 



SOCIETIES AND ACADEMIES. 

 London. 



Royal Society, April 2S. — " On the Changes of Thermo- 

 electric Power Produced by Magnetisation, and their Re- 

 lation to Magnetic Strains." By Shelford Bidwell, F.R.S. 



The experiments described were undertaken with the view 

 of investigating an apparent correspondence to which the 

 author directed attention in an article published October, 

 1902 (" Ency. Brit.," art. Magnetism), between the effects 

 of magnetisation upon thermoelectric quality and upon 

 dimensions. Reference is made to the work of W. Thom- 

 son, Ewing, Chassagny, HouUevigue, and Rhoads. 

 Although some of the results previously recorded appear to 

 be erroneous, it is shown that, at least for iron and nickel, 

 there is an intimate relation between the two phenomena. 



In the case of iron, the relation is not disclosed unless 

 allowance is made for the effect of the purely mechanical 

 compression due to magnetisation. The author pointed out 

 in iSSS {Phil. Trans., vol. clxxix. .\, p. 216) that a magnet- 

 ised iron bar must be subject to a compressive stress, the 

 consequent contraction being expressed as a fraction of the 

 original length by the ratio of the lifting power or " tractive 

 force " to Young's modulus. The tractive force was calcu- 

 lated in an earlier paper (Proc. Roy. Soc, vol. xlvii. p. 486). 



NO. 1807, VOL. 70] 



If a transverse cut is made in a longitudinally magnetised 

 bar, the magnetic force inside the gap is B = H-|-47rI. One 

 portion of the bar being fixed, the force acting upon the 

 face of the other portion is less than B by 2irl, the part due 

 to the face itself ; thus the attractive force per unit 

 area = (B — 27rI)I =2Tp-t-HI. For permanent magnets, 

 when H=o, and for the special case in which each half 

 of the bar is surrounded by a tightly fitting coil, when the 

 term H'/Stt must be added for the mutual action of the 

 coils, this expression becomes B'/Stt, which is sometimes 

 said to represent " Maxwell's stress." The stress between 

 any two portions of a magnetised bar divided by an 

 imaginary transverse plane is sustained by the inter- 

 molecular springs, whatever their physical nature may be, 

 to which the elasticity of the metal is due. Taking Young's 

 modulus in grams per sq. cm. as 2X10°, the extrinsic 

 contraction due to magnetisation, expressed as lo-millionths 

 of length, is (27rI--|-HI)/200g'. Curves were plotted show- 

 ing change of thermoelectric power and change of length 

 in relation to H, and it was found that, if the latter were 

 " corrected " for mechanical stress and the scale of 

 ordinates suitably chosen, the two curves were almost 

 coincident ; without such correction there was no corre- 

 spondence. The change of thermoelectric power due to 

 magnetisation is therefore proportional to the " corrected " 

 elongation, but the factor of proportionality differs for 

 different specimens and for different physical conditions of 

 the same specimen. It is shown in the paper that the two 

 phenomena are analogously affected by tensile stress and 

 by annealing. 



For nickel it appeared, contrary to the accepted view, 

 that the direction of the thermoelectric force was the same 

 as in iron — from unmagnetised to magnetised through hot 

 — whereas the " corrected " change of length is opposite in 

 the two metals, iron being extended, nickel contracted. 

 But the curves for change of length and for change of 

 thermoelectric power were, when one of them was inverted, 

 almost exactly coincident, although no correction was made 

 for the mechanical stress. The question then arises. Why 

 should the correction which is indispensable in the case of 

 iron be unnecessary for nickel? The answer is that while 

 for iron the calculated correction is very considerable 

 (generally, indeed, greater than the observed change of 

 length to which the correction is applied), for nickel it turns 

 out to be exceedingly small ; thus it happens that the un- 

 corrected and the corrected curves, if referred respectively 

 to slightly different scales of ordinates so chosen that the 

 two curves may be of the same height, are sensibly identical. 

 The absence of any need for the correction in the case of 

 nickel, where, a priori, it ought not to be required, tends 

 to show that the success of its application in the case of 

 iron is not a mere accident, and the compressive stress is 

 consequently a vera causa. Some years ago the question 

 of stress in a magnetised metal was discussed by several 

 well known physicists in Nature (vol. liii. pp. 269, 316, 365, 

 462, S33). 3''"1 '' seems not to be agreed whether there is 

 in fact any such mechanical stress ; whether, supposing one 

 to exist, it is compressive or tensile, and whether it is 

 " Ma.xweirs stress " or some other. The author submits 

 that the results of the new experiments support his original 

 view. 



For cobalt no relation between thermoelectric and 

 dimensional changes attending magnetisation could be 

 found ; if any such exists, it is disguised by some cause 

 which has yet to be discovered. 



May 19. — " On Saturated Solutions." By the Earl of 

 Berkeley. Communicated by F. H. Neville, F.R.S. 



June 9. — " Notes on the Statolith Theory of Geotropism. 



I. Experiments on the Effects of Centrifugal Force. 



II. The Behaviour of Tertiary Roots." By Francis 

 Darwin, F.R.S., and D. F. .M. Perti. 



The facts given in the paper prove that when the primary 

 root is removed and a secondary root assumes its place, the 

 tertiary roots take on the character of normal secondaries. 

 It may be believed, therefore, that the existence of stato- 

 liths in normal tertiary roots is a provision enabling them 

 to assume diageotropic growth in case of injury to the 

 primary root. This, though appearing a bold conclusion. 



