June .^. 1920] 



NATURE 



439 



ferro-nickel alloys, his first experiments were on their 

 magnetic properties, as these were easier to investigate 

 than the coefficients of expansion. Dr. Guillagme 

 showed and explained curves representing the varia- 

 tion of magnetic properties, and of the coefficients o 

 and fi in the expansion equation l = l^{i + a& + ^0^) for 

 alloys in both the irreversible and reversible categories, 

 and showed from the curves how it was possible to 

 obtain alloys with any desired coefficient. The 

 anomalous magnetic behaviour of some of the alloys 

 was illustrated by demonstration experiments of the 

 effect produced on the magnetic condition of bars 

 of the materials by dipping in hot water or liquid air. 

 The lecturer then dealt with the properties of ternary 

 alloys containing iron, nickel, and a third element. 

 Manganese alloys were those most extensively used. 

 He exhibited a cardboard model of Guthrie's three- 

 dimensional diagram for ternary alloys. The addition 

 of the third element raised the minimum expansion. 

 In the case of carbon and chromium the elastic con- 

 stant is raised. The curve connecting Young^'s 

 modulus with the percentage of nickel in ferro-nickel 

 alloys also showed an anomaly in the same region 

 as the expansion. 



The chief weakness of the alloys from the point 

 of view of the metrologist was instability. If a piece 

 of invar was cooled from a high temperature in air 

 at ioo° C. its length reached a steady value in about 

 loo hours. If it was then cooled to 50° C. its length 

 would increase to another steady value, reached in 

 about 1000 hours or so. If it were then cooled to 

 zero it would still further lengthen, a steady state 

 not being reached for a very long time. If the tem- 

 perature were then raised again to 100°, the length 

 would diminish to its initial value for 100°. The total 

 change of this character between 0° and 100° 

 amounted to about 30 millionths of the length. 



With increasing carbon content the instability verv 

 rapidly increased. It was possible from the amount 

 of the instability to estimate the carbon to i/iooth per 

 cent. Moreover, the curve connecting the instability 

 and the carbon content passed through zero, showing 

 that the instability was due to the carbon. It was 

 therefore possible to get an invar of perfect stability. 



Among the applications to which invar had been 

 put, the lecturer instanced pendulum rods, leading in 

 wires for electric lamps (an alloy being chosen from 

 the curves so as to have the required coefficient of 

 expansion), wire standards for base measurements 

 in surveying, etc., and showed curves of the variation 

 of height of the Eiffel Tower with temperature, as 

 measured relatively to invar wires. 



Another important application of these alloys was 

 in chronometer construction. The temperature co- 

 efficient of the rate of a watch was due to variation 

 of the elasticity of the hair-spring. This was cor- 

 rected in the Graham compensation bv a variation of 

 .Tngular momentum of the balance wheel, depending 

 on the difference in expansion of two metals; but it 

 was possible to choose for the spring a nickel steel 

 having a temperature coefficient of elasticity nearlv 

 zero. If chosen to give the same rate at 0° and 30°, 

 there would be a secondary error of only 20 seconds 

 per day at 15°. But a more important chronometric 

 anplication was the correction of the secondary error 

 of 2 seconds in Graham's compensation. This error, 

 discovered by Dent in 1832, is due to the fact, that 

 the variation of elasticity of the hair-spring is not 

 a linear function of the temperature, whereas the 

 variation of angular momentum of the balance wheel 

 is. If, however, for one component of the bimetallic 

 compensator a nickel steel of negative /8 be chosen, 

 it is possible to get a curve connecting the momentum 



NO. 2640, VOL. 105] 



with temperature which exactly compensates the 

 elasticity variation over the whole range. 



Reverting to the curves for Young's modulus, the 

 lecturer predicted that an alloy would shortlv be pro- 

 duced having a practically constant modulus over 

 a range of 200° C. 



T' 



Technical Education and Mind Training. 



HE proceedings of the annual conference of the 

 Association ot Teachers in Technical Institutions, 

 which was held in the Polytechnic, Regent Street, 

 London, on Whit-Monday, were full of interest. The 

 president, Mr. E. L. Rhead, of Manchester, gave a 

 stimulating address, in the course of which he reviewed 

 unfavouraoly the attitude of the Workers' Educational 

 Association towards technical education as tending to 

 narrow the workers' educational outlook, and as 

 merely serving to create a human tool better calculated 

 to promote the interests of employers and the sordid 

 aims of industry. He claimed, on the contrary, that, 

 rightly presented, technical education has in it' all the 

 elements of mind training and of a wide view of life 

 and its problems. It may, in short, be, properly inter- 

 preted, constituted as the pivot of a liberal education. 

 He deprecated the exclusive devotion of much of 

 modern higher education to dead languages, dead his- 

 tory, and ancient philosophy, but that is surely to 

 ignore a prime element in the evolution of mankind — 

 the progress of man in his endeavour to search into 

 and to solve the phenomena of Nature. Mr. Rheadwent 

 on to consider the status of the technical teacher as 

 compared with that of the secondary-school teacher, 

 and contended that the former should be at least as 

 liberally considered as the latter, not only by reason 

 of his long and arduous practical training in the pro- 

 cesses of industry, but also in respect of the claims of 

 industry itself upon his services. He urged the desir- 

 ability of transfer from lower to higher schools at 

 different periods in the course of the educational life 

 of the capable pupil, and especially dwelt upon the 

 value of the junior technical school, which he would 

 in no wise desire to convert into a trades school, and 

 pleaded that restrictions on their present aims and 

 curricula should be removed. A far more liberal 

 system of scholarships, including maintenance, should 

 be established in co-operation with widely extended 

 administrative educational areas, which should have 

 regard not only to the pupils in day institutions, but 

 also to the equally urgent requirements of the pro- 

 mising evening students, enabling them to devote 

 themselves to whole-time study in their special voca- 

 tion. Ther« should likewise be an efficient repre- 

 sentation of teachers on all education authorities, 

 so that the present and future problems of technical 

 education should be better considered. Resolutions 

 were nassed urging a la'-i?e increase in salaries for the 

 several grades of technical teachers ; that all works 

 continuation schools should u't'mately be provided bv 

 the local education authorities and the present 

 schools be open to inspection by the local and central 

 authorities : and that a national Whitley council for 

 tAanh«rs should be set up. 



University and Educational Intelligence. 



Cambridge. — Prof. J. T. Wilson, professor of 

 anatomy in the University of Sydney, has been elected 

 to the chair of anatomy rendered vacant by the death 

 of Prof. A. Macalister. 



We are informed by the secretary of the Cam- 

 bridge Philosophical Society that the adjudicators of 



