December 12, 1912] 



NATURE 



42: 



quartz plate, which is polished so as to act as a mirror, 

 to undergo a rotation about an axis in the plane of 

 the polished surface. 



Dr. T. M. Lowry described some very accurate 

 determinations of the optical rotatory power of quartz, 

 in which particular attention was paid to the purity 

 of the quartz, and to obtaining light pure enough to 

 give a clean extinction when reading a rotation of 

 several thousand degrees, and of sufficient intensity 

 to be read with a small half-shadow angle. 



Prof. R. A. Sampson, in giving a short account of 

 a paper on the calculation of the fields of telescopic 

 object glasses, remarked that the object of long-focus 

 lenses vi-as not to diminish the effects of chromatic 

 aberration, but to do so for the other types of aberra- 

 tion. 



Prof. D. C. Miller showed a very ingenious and 

 successful instrument for analysing sound vibrations. 

 The membrane set vibrating by the source of sound 

 tilts a mirror mounted on an axle. The essential 

 feature of the instrument is the extreme minuteness 

 of the mirror, which, together with the axle on which 

 it is mounted, does not weigh more than two milli- 

 grams. The light received from the mirror is received 

 bv a second mirror continuously rotating round a 

 perpendicular axis. Vibration curves were projected 

 on to a screen, the amplitude being about two feet, 

 and the length shown some twenty feet. The con- 

 stitution of compound notes was thus instantly 

 demonstrated, and in particular the constitution of 

 vowel sounds. 



In the report of the committee on electrical 

 standards evidence is given of the satisfactory char- 

 acter of the methods which have been established, in 

 a great measure by this committee, for the measure- 

 ment of electrical quantities. The committee rightly 

 considers that the primary objects for which it was 

 appointed have been achieved. It has, however, 

 been reappointed for another year in order to complete 

 the business arrangements connected with the re- 

 publication of the entire set of its reports from 1861 

 until the present time. 



In a report of the committee to aid in the work of 

 establishing a solar observatory in Australia, it is 

 reported that the Commonwealth Government ap- 

 pointed a board to inquire and report upon the best 

 site for an observatory within the federal territory 

 at Yass-Canberra. They unanimously selected a site 

 on the summit of a hill some 2500 feet above sea-level, 

 and the Government has instructed Mr. Baracchi to 

 establish a temporary observatory at the selected site, 

 and to determine definitely whether it answers the 

 requirements of modern scientific research, including 

 astrophysics. The telescope is the gift of Mr. James 

 Oddie, of Balarat, who offered it, together with other 

 instruments, for this specific purpose. A 6-inch Grubb 

 refractor, the gift of the trustees of the estate of the 

 late Lord Farnham, is also to be forwarded to 

 Australia. In view of the action now being taken by 

 the Commonwealth Government, there can be no 

 doubt of its intentions in the matter of solar work. 



Atomic Heat of Solids. 

 The second formal discussion which had been 

 arranged was on the atomic heat of solids. This was 

 opened by Dr. F. A. Lindemann, of Berlin. If the 

 ordinary principles of mechanics are admitted as 

 governing the movements of atoms, equipartition of 

 energy is bound to be attained, and the atomic heat 

 of a solid at constant volume should be exactly -^R. 

 To escape from Rayleigh's formula for the distribu- 

 tion of energy in the spectrum, Planck has assumed 

 that an oscillator may only emit definite discontinuous 

 quantums of energv, and shows that their magnitude 



NO. 2250, VOL. 90] 



is proportional to the frequency ; and he develops the 

 formula — ■ 



r- 2C^/l I 



where h is a new universal constant 6'S5xio-^' erg. 

 sec, K = R/N, and ;' is the frequency. This formula 

 appears to agree with experimental results. From 

 this, on certain assumptions, Einstein has shown that 

 the atomic heat of N atoms should be — 



where a = (/;i')/(KT). 



This formula is only approximately correct, and fails 

 altogether if one inserts the true frequencies calcu- 

 lated from the reststrahlen, from the compressibility, 

 density and atomic weight, or from the melting point, 

 density and atomic weight. Nernst and Lindemann 

 have empirically modified this formula by adding a 

 second term in which a has half the value in the first, 

 thus corresponding to frequencies an octave below 

 those in the first term. This formula holds accurately 

 for the atomic heat of the metals, diamond, NaCl, 

 KCl, NaBr, and KBr, using the values of v given 

 by the reststrahlen. 



It follows that the free electrons, if there are any, 

 can only have a very small specific heat, for the 

 atomic heats of conductors and non-conductors may 

 be represented by practically identical curves. Further, 

 it can be shown that " Nernst's theorem" is a conse- 

 quence of the fact that the atomic heats are infinitely 

 small aL-the absolute zero. 



In the discussion, Dr. G. E. Gibson sketched an 

 hypothesis by means of which the difficulty of Planck's 

 assumption of a discontinuous absorption and emission 

 of energy might be removed. He supposes that the 

 discontinuity is confined solely to the collisions be- 

 tween the molecules with which the resonators are 

 connected, so that during the time between collisions 

 the resonators are subject to the ordinary laws of 

 thermodynamics. 



Lord Rayleigh was glad that, though the law of 

 equipartition led to his own equation, this liad not been 

 so presented as to make it appear that he believed 

 it to apply to all wave lengths. He considered that 

 the difficulty attending the five degrees of freedom 

 of a diatoniic gas had not yet been removed satis- 

 factorily. However stiff the molecule is made axially 

 there is still a degree of freedom connected with axial 

 separation of the two atoms. He was extremely 

 interested in the quantum theory; the success it had 

 obtained showed that it should not be given up, 

 although at the same time it seemed to be throwing 

 away most of our dynamical ideas. It implies the 

 extraordinary result that when two molecules meet 

 they may not take up motion because it is too small 

 to be taken up at all ! 



Dr. ■ J. W. Nicholson laid emphasis on the dis- 

 crepancy between Lindemann 's conclusion that the 

 atomic heat of electricity is very small and the usual 

 conclusion from the electronic theory of metals which 

 requires a value for it so large as to be inadmissible. 

 He felt very much in accord with the ideas put for- 

 ward bv Dr, Gibson. 



Prof. Rutherford said that one point appealed to 

 him. Foreigners seem to be content without realising 

 a practical model or mechanism of the processes they 

 assumed to take place. He did not lay great stress 

 on the agreement between the theory and experiment 

 — a double exponential equation can be fitted to almost 

 anything. He was inclined to doubt whether the 

 formula of Nernst and Lindemann was of the right 

 form. 



