July 3, 1890] 



NA TURE 



239 



Physical Society, June 6.— Prof. W. E. Ayrton, F.R.S., 

 President, in the chair. — Mr. H. Tomlinson, F.R.S.. read a 

 paper on the effect of change of temperature on the Villari 

 critical points of iron. This, he said, was a continuation of the 

 paper he read before the Society on March 21, and the method 

 employed was the same as then described (see Phil. Mag., vol. 

 xxviii. p. 394). Since then, however, he has made experi- 

 ments at various temperatures up to 285° C, the temperature 

 being determined from the resistance of a platinum wire whose 

 temperature coefficient was carefully determined. The follow- 

 ing table shows some of the results obtained with a well- 

 annealed iron wire i mm. in diameter, which had been re- 

 peatedly heated up to 300° C, and cooled to the temperature of 

 the room until the temporary permeability with various loads 

 attained constant values at both temperatures. 



Curves from which these numbers were obtained are given in 

 the paper, and in these the load in kilogrammes, and percentage 

 change of temporary permeability are plotted. From these 

 curves and table it will be seen that if the first points in which 

 the curves cut the load-line be considered, then at all tempera- 

 tures the Villari values increase as the load decreases. If, how- 

 ever, the second points be taken, the critical values increase 

 both with load and temperature. In both cases the Villari 

 value is increased by rise of temperature. From the curves it 

 follows that rise of temperature reduces the total variation of 

 permeability produceable by loading. A table showing the 

 temporary permeability of the unloaded wire at the various 

 temperatures accompanies the paper. — A paper on the diurnal 

 variations of the magnet at Kew, by W. G. Robson and S. W. 

 J. Smith, was communicated by Prof. Riicker. In some pre- 

 liminary remarks the Professor pointed out the great advis- 

 ability of having the results of magnetic observations at various 

 Observatories reduced and published in the same manner, and 

 for the same periods. In order that this may be effected, the 

 methods of reduction must be trustworthy, but not very elaborate. 

 The Greenwich plan is too laborious to be generally adopted, 

 but the method suggested by Dr. Wild (Rep. Brit. Ass., 1885, 

 p. 78}, in which the mean diurnal variation is obtained from 

 measurements on five quiet days in each month, is feasible. With 

 a view to further testing the trustworthiness of this method, the 

 work described in the paper was undertaken. Mr. Whipple had 

 made a comparison of the two methods for the years 1870-71-72, 

 with the result shown in the following table : — 

 Minutes of arc. 



K, - K«, = 07 



G - K^ = 1-2 



G - K,„ = 1-6 

 where K^ is the mean diurnal range at Kew as obtained by 

 Sabine's method, K-^ that obtained by Wild's method, and G 

 that obtained at Greenwich by the Greenwich method. He also 

 found that the mean hourly differences followed some definite 

 law. The authors undertook the reduction of the Kew observa- 

 tions according to Wild's method for the years 1883, 1886-87 ; 

 the first was chosen as being a year of maximum sun-spots. The 

 results give — 



Minutes of arc. 

 1883 ... G - K„, = I -5 



1886 ... G - K«, = 1-2 



1887 ... G - K,„ = 1-9 



There is thus a difference of nearly two minutes in the variations 

 at the two places, and this cannot all be accounted for by the 

 method of reduction. Another peculiarity is that the range, as 

 calculated by Wild's method, is greater by about o'-5 than that 

 obtained by the Greenwich method, although the latter includes 

 'i.iys of moderate disturbance. The total range at both places 

 has diminished by about i'-6 between 1883 and 1887. The 



NO. 1079, VOL. 42] 



paper is accompanied by tables and curves plotted from the 

 differences in the mean hourly readings at Greenwich and Kew 

 for each of the above 6 years, and a marked similarity exists 

 between all of them. The mean of the 6 curves differs in no 

 case by more than o'-4 from the curve for any year. It is thus 

 possible to calculate the Greenwich values from the Kew num- 

 bers ; and as these latter are published about two years sooner 

 than the former, this fact may be very important. Referring 

 to the reduction of results. Prof. Riicker said that the Stonyhur.st 

 observers and Prof. Mascart were willing to adopt Wild's 

 method ; F.almouth, he hoped, would follow suit, and Green- 

 I wich had been asked to publish their results in both ways, Mr. 

 Whipple said that, before recording-instruments were available, 

 I and the numbers were obtained from separate experiments, the 

 labour involved was considerable, and a single large disturbance 

 { or magnetic storm might vitiate the result of a whole year's 

 work. Methods were therefore adopted to eliminate these dis- 

 I turbances ; of these, that used by Sabine may be particularly 

 j mentioned. Although declination records have now been ob- 

 ' tained for a considerable number of years, the cause of the 

 variations still remains unknown. They do not seem to be 

 dependent on temperature or on astronomical facts. He con- 

 sidered it valuable to obtain magnetic data from different 

 parts of the earth, but comparisons were only possible when 

 all are published on the same plan. This, he hoped, would 

 result from the efforts of Profs. Rucker and Adams. When 

 this is accomplished, the observations on magnetic force 

 will need treatment ; this work will be laborious, and the 

 aid of volunteers like Messrs. Robson and Smith would 

 be of great service. Prof. W. G. Adams said he was 

 glad to see the satisfactory nature of the work which had 

 just been brought before the Society. Usually, the mass of 

 figures to be dealt with was so large that the mere reduction was 

 a great undertaking. If, however, the difference between results 

 obtained by the Greenwich and Wild's method was not more 

 than o'-4, it maybe possible to make out the causes of the varia- 

 tions from observations reduced on Wild's plan. He himself would 

 put more faith in horizontal force observations, and wished they 

 could be worked out by some ready method. He hoped the one 

 adopted in America, of obtaining mean curves by photography, 

 might prove satisfactory. Prof. Perry asked if a machine could 

 not be made to do the work. Mr. Whipple said such machines 

 had been used by the Meteorological Office, but they were so 

 el aborate and expensive that clerical work was just as cheap. 

 The method of photographing mean curves had been tried at 

 Kew, but it was open to the objection that accidental disturb- 

 ances, such as those produced by the movement of iron in the 

 vicinity and the approach of cabs, &c., were not eliminated. 

 Mr. Boys, referring to the use of integrators, said that, for an 

 harmonic analyaer, his disk-cylinder pattern was preferable to 

 the ball-disk-cylinder integrators of J. Thomson, for it was much 

 cheaper, and had less inertia. The President said the movement 

 initiated by Prof. Riicker would be of great service if it re- 

 sulted in the numbers obtained at the various magnetic Observa- 

 tories being published in the same way. It was a great advant- 

 age to have such men, who were not permanently attached to 

 an Observatory, to take up the subject and suggest improve- 

 ments. The heads of such institutions were usually too much 

 employed in making the necessary reductions to have time for 

 devising improved methods. In his opinion, greater freedom 

 should be allowed to the chiefs of Observatories, for it should 

 be borne in mind that the object of observations is not to produce 

 volumes of figures, but to increase our knowledge. Referring to 

 the reduction of observations, he thought the voluntary services of 

 senior physical students should be more generally accepted, and 

 to this end he suggested that properly recommended persons 

 should be a.llowed to spend some time in Observatories as 

 honorary assistants. This would be of great use to the students 

 themselves, and an advantage to the Observatories, for the re- 

 duction of observations could then be expedited. As regards 

 the accidental disturbances referred to by Mr. Whipple, he 

 contended that regulations should be adopted to render them 

 impossible. 



Zoological Society, June 17.— W. T. Blanford, F.R.S., 

 in the chair.— Mr. Sclater exhibited and made remarks on a 

 mounted head of a Pallah Antelope, obtained by Captain F. 

 Cookson, on the Cunene river, in South-western 'Africa, which 

 was distinguished by its black face from the ordinary form of the 

 Cape Colony. — Mr. Sclater also exhibited a large photograph of 

 Grevy's Zebra {Equus grevyi), taken from the specimen in the 



