360 



NA TURE 



[September 9, 1922 



Sydney Observatory, but soon gave it up to enter as a 

 student at the University, to the great regret of the 

 Government Astronomer, II. ('. Russell. He took the 

 B.Sc. u ith tin- university medal for physics in 1889, and 

 in 1890 was appointed demonstrator in physics under Sir 

 Richard Threlfall, who at that time occupied the chair of 

 experimental physics. I In Threlfall's return to England 

 in 1899 Pollock succeeded to the professorship, which 

 he held up to the time of his death. He was president 

 of Section A of the Australian Association for the 

 Advancement of Science in 1009. was secretary of the 

 Royal Society of New South Wales Eor the lasl eleven 

 years of his life, and was elected K.R.S. in 1916. 



When tin' Australian Maine' Uallalion was formed 

 for work in France about 1915, Pollock at once joined 

 with the rank of captain — the fact that he was fifty 

 years old al the n n naturall) made no difference to 

 a man of his character. Soon after he gol to France 

 he was put in 1 harge ol the si hoof for training offii er 1 

 in " li tening " underground by means of geophones 

 and related devices. The si hool was near Poperinghe, 



within easy reach of Messines and other points of (In- 

 line where tunnelling was in progress, and he took his 

 lull share in the nervous work of estimating how near 

 our tunnels were to the German works. It was char- 

 acteristic ol him that having noticed that in binaural 

 listening with geophones some observers were much 

 more effective than others, he used his opportunities 

 to estimate the minimum retardation oi phase which 

 would cause the sound to go " round the head." lie 

 finally discovered a young Russian who was so sensitive 

 thai he could poinl I he geophone indicator in the 

 direction of the sound with an accuracy of the same 

 order as is attainable by visual means ! 



After the mining period was over Pollock was moved 

 to Farnborough, where he worked at the problems of 

 aeroplane navigation with the rank ol major until the 

 end ol the war; but his real contribution to the final 

 victor} lay in the way he conducted the school at 

 Poperinghe, where all instruction in "listening" was 

 practically in his hands. 



Pollock's experimental work in physics, contained in 

 some twenty papers, is characterised throughout by 

 his striving Eor accuracy and the avoidance of ambiguity. 

 His earl) training at an observatory coloured all his 

 work. Whatever the apparatus was, the best result 

 must be got out ol it, and when the work was published 

 nothing must appear thai was not really essential. 

 Bis skill in adjusting instruments has probably scarcely 

 ever been equalled, as may be seen by reference to a 

 joint papei on a gravit) balance (Phil. Trans., 1899, 

 Vol. A, [93). In this work, whatever degree of success 

 was attained may be attributed mainly to Pollock's 

 skill and devotion : the late Mr. Duddell — no mean 

 judge in such matters — once told the writer that had 

 the thing not been done he should have regarded it as 



impossible. 



I>iii lie- the years J890 to 1895 Pollock was greatly 



interested in optica] experiments. He had acquired 

 great skill in making the adjustments required when 

 using the Miehelson Morley classical apparatus, and 

 with it made lome observations oi the effect of the 

 velocity of a stream oi water on light passing through 

 it. Like many other of his experiments no publication 

 was made, because he considered that the conclusions 



NO. 2758, VOL. I IO] 



he came to did not constitute an advance on existing 

 knowledge. 



After 1900, for some years Pollock's work was mainly- 

 directed to establishing the relations between the 

 geometrical constants of a conductor and the wave- 

 length of the electromagnetic radiation obtained from 

 it. The accurate figures obtained were very welcome 

 at the time, and he returned to the subject at a later 

 dale. The apparatus was then used for the determina- 

 tion of the specific inductive capacitv of a sheet of glass 

 at high frequency 24,000,000 (Pollock and Vonwiller). 

 Measurement was repeated at a frequency of 50, and 

 no appreciable difference in specific inductive capai it) 

 was found. This work was then extended to Selenion 

 by Vonwiller and Mason as a supply of well-purified 

 material was available. The value obtained, again 

 practically the same whether the frequency was high 

 or low, namely, 6-13 at 16° C. by low Erequeni 5 and 6- 1 1 

 by high frequency at 23-6" ( '., is probably the most 

 trustworthy figure extant for the material in the 

 ph) ii al state desi ribed in the paper. As the measure- 

 ment was not made in Germany, it is doubtful w hether 

 it will ever reach a text-book. 



The above investigations were followed by an 

 experimental and theoretical investigation of the 

 application of the ionic theory of conduction to the 

 carbon arc — especially in regard to the phenomena of 

 " n lighting " (Pollock, Wellisch, and Ranclaud), 1909, 

 but lor several years Pollock's experimental work was 

 much interrupted by the illness of his brother, to whom 

 he was devoted and to whom much of his scanty leisure 

 wa: given he died some years ago. 



Probably the most important work done by Pollock 

 was his investigation of the ions of the atmosphere 

 {Phil. Mag., 20, 1915, pp. 514 and 636, and Proc. Roy. 

 Soc. N.S.W., Oct. 1909). Starting with the "large ions" 

 di covered by Langevin, Pollock showed that their 

 mobility was definitely related to the relative humidity 

 of the air; applying a thermo-dynamic argument to 

 his observations he concluded that the large ions con- 

 densed water in the liquid phase. He then discovered 

 a new class of ions intermediate in mobility between 

 Langi -\ m's ions and free ions, and by the same thermo- 

 dynamic argument indicated that in this case the ion 

 was weighted with water in the vapour phase. 



The two papers quoted give a very good idea of 

 Pollock's powers as a physicist, since he allowed his 

 scientific imagination more scope than usual. Among 



nun Hitributions his description of an automatic 



Sprengel pump and an investigation of the mode of 

 formation of very small bubbles in frothing solutions 

 ma) be mentioned. In fact, his exposition of froth 

 formation (Phil. Mag., 1912) is exceptionally clear 

 and judicious. 



In 1914 Pollock returned to his observations on the 

 relation of the length of electromagnetic waves to the 

 length ol a " straight terminated " rod in which they 

 are generated, and more recently was applying his 

 experience in acoustics, obtained during the war, to 

 the investigation of the action of the stethoscope and 

 to the study ol the velocity of sound through earth. 



\ , a 1 olleague Pollock was ever cheery and obliging, 

 but his (din icons manner covered a character ol great 

 firmness, and if he had once made up his mind as to the 

 propriety ol any line of conduct he could not be turned 



