4-1 I 



NATURE 



[February 6, 1919 



LETTERS TO THE EDITOR. 



\i'h, Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or any other part of Nature. No not 

 taken of anonymous communications.] 



End-Products of Thorium. 

 MR. J. R. Cotter's letter on this subject (Nature, 

 Januarj 30), stating thai he h is been unable to 

 detect the presence of thallium in thorianite, and is 



confident that il doe- n,,i , main urn (.■uus per cent., 



is in accord with othei evidence of which I have been 

 given private information. I may say, however, that 

 the actual amount of thallium I separated from 

 -'" kilograms of thoriti was very small, certain!} less 

 than 0-005 I"' cent., though no particular precautions 

 were taken to i (Ted a quantitative separation, as its 

 presenci ■■■ detected during the working up of 



•he whole qu i\ For lead. Prof. Joly has pointed 



out (Nature, June 7, 1917) that the hypothesis of the 

 instability of the major end-product of thorium in- 

 volves the explanation of the disappearance from the 

 ilograms of mineral of 150 grams of unstable 

 lead, whereas the structure of the thorium halo gives 

 no support to the view that unknown o-ray changes 

 occur in the thorium series. 



Not only against the particular suggestion as regards 

 thallium, but also on the general one that one of 

 the end-products of thorium is unstable, the evidence 

 appears now to be against the view. I have no new 

 observations to oiler, but Mr. Lawson, writing to me 

 recently from the Radium' Institut, Vienna, refers to 

 researches carried out there by Prof. Meyer and others, 

 from which the- conclusion has been drawn that both 

 the isotopes of thorio-lead appear to be stable. 

 Referring to elements which an unstable lead could 

 conceival>lv produce, he mentions my observation of 

 the presence of appreciable quantities of iodine in 

 thorite and the possibility that this ma\ be " eka- 

 iodine" of atomic number 85. I may sav that this 

 point was thoroughly investigated four years ago by 

 Mr. J. A. Cranston, who determined its atomic weight, 

 and found it to be that of ordinary iodine. 



Frederick Soddv. 



The Neglect of Biological Subjects in Education. 



PROF. Boycott's letter on this subject in Nature of 

 Januarj 23 deserves the serious attention of those who 

 striving to secure, as an element in our higher 

 education, some sound knowledge of elementary 

 science and of true scientific method of thought. Quite 

 apart from the important and useful information which 

 would h< ineidentalh acquired from well-directed bio- 



logji il h 11 King', the student would thus receive an 

 excellen hooling in bow to think clearly. It is oon- 

 stanth that an immense proportion of the 



subject-matters which concern human beings in their 



everyday I n the " biological " side of the 



border-line which conventionally divides them from the 

 domain of " physics." 



It has frequentl been shown bow ignorant manj 

 nun in very high place* are of the elements oi chem- 

 istry and physic-. Ti illustrate such lack of know- 

 ledge of simple biology would be a very easy task. 

 Put the value of some realh sound instruction in bio- 

 logy, even onlj .1- a mem,,! ining, should be widely 

 recognised. II. Bri \n Donkin. 



London, January 30. 



NO. 2571, VOL. I02] 



Scientific and Practical Metric Units. 



In the article entitled "Scientific and Practical 

 Metric Units" which appeared in Nature of Octo- 

 bei 1. "n*, reference is made to the convenient 



i I ic system which exists in the ton, 



and Che author asks for a convenient monosyllabic 

 name for a weight of about 2-2 lb. I would commend 

 loi consideration the word "seer." The Imperial 

 Indian seer, in common use all over India on the 

 railways, weighs 205 lb., and would be as convenient 

 a bridge to the metric system for India a- the ton 

 would be at home. 



In many parts of Madras the local measuring seer 

 for grain weighs a little more than 2 lb. 



G. R. Hilson, 

 Deputy Director of Agriculture. 



Bellary, Madras, S. India. 



December 7, j < p 1 s . 



THE ECLIPSE OF THE SI N ON MAY 29. 



IT has been found impossible to organise any 

 British solar eclipse expeditions .since those 

 sent to Sweden and Russia in the summer of 

 1914, just before the threat of war arose. Conse- 

 quently, advantage is being taken of the cessation 

 of hostilities to arrange for the occupation of two 

 stations in the eclipse of next May by parties sent 

 out by the Joint Permanent Eclipse Committee 

 of the Royal and Royal Astronomical Societies. 

 This eclipse is noteworthy for the long duration 

 oi totality, which is 6m. 50s. in mid-Atlantic, and 

 5m. 13s. at each of the selected stations. The 

 duration of totality in the eclipses of the same 

 series in the Saros cycle has been gradually in- 

 ! creasing, and will reach a maximum of about 

 7m. Ss. in June, 1955, in the neighbourhood of 

 Manila; this duration will exceed that of any 

 eclipse in the preceding millennium. 



The track of totality next May crosses the 

 entire breadth of South America and Africa. For 

 stations of tolerable accessibility and sufficiently 

 high sun, our choice is restricted to north- 

 eastern Brazil and equatorial West Africa. There 

 is a rather serious error in the maps of the 

 eclipse printed in the ephemerides ; they indicate 

 the track of totality as lying to the south of the 

 Liberian coast, but totality will, in fart, be ob- 

 servable on that coast, and the duration of totality 

 and height of sun are greater than at any other 

 land station. However, the weather prospects 

 are not favourable, and it is not proposed to 

 occupy a station there. The selected Brazilian 

 station is Sobral, in Ceara, abouwSo miles inland, 

 connected by railway with Camocim, which is 

 reached by steamer from Para. Messrs. Crom- 

 rnelin and Davidson, of the Royal Observatory, 

 Greenwich, are going there, while Prof. Eddington 

 and Mr. Cottingham will occupy the Portuguese 

 island of Principe, 1 10 miles distant from the 

 African coast, which is reached bv fortnighth 

 steamer from Lisbon. 



Other possible stations are the African coast, 

 near Libreville, or the high ground to the west 

 of Lake Tanganyika. The weather prospects at 

 the latter place are the best along the track of 



