April 8, 1909] 



A' A TURE 



159 



we find hitherto an empty place, an element stands possess- 

 ing an atomic and molecular weight of 0'4, and he adds 

 that this clement might be identical with Young's 

 " coronium." This part of the periodic arrangement is : — 



As there must be a definite ratio between the densities 

 of the four gases A, B, C, and D and their radius of 

 rotation corresponding to their maximal molecular con- 

 centration, it is not impossible that from the data obtained 

 by Wolf the density of the lightest gas, i.e. its molecular 

 weight, which must be identical with its atomic 

 weight, might be calculated. As regards the heaviest 

 unknown gas, D, if this is not a gas of the helium-argon 

 group we may be allowed to point out that the existence 

 of a gas possessing a larger atomic weight than hydrogen 

 and a smaller atomic, but a larger molecular, weight tlian 

 helium is not absolutely excluded. 



BOHUSLAV Brauner. 



Bohemian Unirersity, Prague, February 27. 



On the a Rays from Radium B. 



A ri;cF.NT number of the Physihalische Zeitschrift (x., 46, 

 1909) contains an article, by Frederic A. Harvey, in which 

 he states that radium B gives out a particles, the ionisation 

 range of which in air lies between 26 mm. and 3-0 mm. 

 In investigating these sliort-range a particles he used a 

 modification of the method employed by Bragg and Klee- 

 man (.Phil. Mag., x., 3:8, 1905), but on account of the 

 limited range of the radiation he did not use a cone of 

 rays. 



Some time ago the writer (Phil. Mag., xi., 806, 1906) 

 investigated the same subject by an entirely different 

 method, and reached the conclusion that radium B did 

 not give out o particles with sufficient velocity to ionise 

 the air. I have recently repeated Harvey's experiment, 

 but have been unable to get any indication whatever of 

 the presence of short-range a particles. In addition to 

 this, I have employed a third method, which eliminated 

 most of the difficulties inherent in the previous one. 



The principle of the method is very simple, and involves 

 no change in the position of the testing vessel or wire 

 during the experiment ; it is based on the fact that the 

 range of the a particles is increased by reducing the 

 pressure of the air. The two plates of my testing vessel 

 were placed 5 mm. apart ; the lower one, which was of 

 wire gauze, was 5 mm. above the active wire. Now, if 

 none of the a particles present had a range in air at 

 atmospheric pressure of less than 10 mm., then the ionisa- 

 tion current should vary as the pressure. If, however, 

 radium B gives out a particles having a range of about 

 2-5 mm., and if they produce about the same number of 

 ions per cm. of path as the a particles from radium C, 

 then, after the pressure is reduced to half an atmosphere, 

 the short-range a particles will begin to enter the testing 

 vessel, and the ionisation will remain constant until the 

 pressure has fallen to a quarter of an atmosphere. At this 

 point the path of these a particles will extend through the 

 entire depth of the testing vessel, and as the pressure is 

 still further decreased the ionisation will again become 

 proportional to the pressure. 



The results of this experiment have shown that the 

 ionisation in the testing vessel is approximately propor- 

 tional to the pressure of the air from 76 cm. to 3 cm. It 

 would, therefore, seem fair to conclude that there was not 

 present on the active wire any substance giving out 

 a particles which had a range in air from i mm. to 5 mm. 



It should also be pointed out that Harvey's reason for 

 attributing the short-range a particles to radium B is at 

 fault. He assumes that after 140 minutes radium B has 

 practically disappeared, and that only radium C remains. 

 The theorv of radio-active transformations, however, re- 



NO. 2058, VOL. 80] 



quires that, after 140 minutes, the number of atoms of 

 radium B and radium C changing per second shall be very 

 nearly the same. Howard L. Bronson. 



McGill University, Montreal, March 20. 



British Association — Winnipeg Meeting. 



It is becoming more and more noticeable at the meet- 

 ings of the association that communications are read 

 which are of special interest to members of sections other 

 than that to which each of the papers happens to be pre- 

 sented. In fact, there is little doubt that interests are 

 now far too much subdivided at our meetings, and that 

 one of the main purposes of the association is therefore 

 unfulfilled. Many of us have felt the desirability of 

 associating sections for the consideration of topics of 

 common interest — not merely for set debates. 



I am glad to say that the arrangement is being made 

 that at Winnipeg Sections A and B shall sit together on 

 the Friday ; Sections B, K, and the Subsection of Agri- 

 culture on the Monday ; Sections B and I on the Tues- 

 day. Wheat is to be the main subject of consideration 

 on the Monday, and food on the Tuesday. It is hoped 

 that it will be possible to treat these two important topics 

 somewhat fully, so as to present, in abstract form, a clear 

 statement of our present state of knowledge, and thereby 

 guide public opinion as well as influence inquiry. 



Henry E. Armstrong. 



Fluorescence of Lignum Nephriticum. 



MusscHENBROEK, referred to by Mr. Shaxby in Nature 

 of April I (p. 12S), is evidently quoting from Boyle's 

 memorable experiment, nearly a hundred years earlier. 

 Mr. Shaxby will find it in the fifth volume of Boyle's works 

 as follows : — 



" If you make an infusion of Lignum Nephriticum in 

 spring water it will appear of a deep colour like that of 

 oranges when you place the vial between the window and 

 your eye, and of a fine deep blue when you look on it 

 with your eye placed between it and the window " 

 (" Experimenta et Observationes Pliysica; "). 



The history of the discovery is so fully dealt with in 

 Tyndall's well-known lectures on light that it is sur- 

 prising that anyone should imagine that Sir David 

 Brewster was the first to observe fluorescence. 



The Lignum Nephriticum is the Indian horse-radish 

 tree, still cultivated for its fruit, which is eaten as a 

 vegetable or pickled. The root has a flavour similar to 

 that of horse-radish, and its title, nephriticum. is derived 

 from the belief of the old pharmacologists that it was 

 useful in cases of disease of the kidneys. 



Ch.wles E. Benham. 



Essex County Standard Office, Colchester, April 3. 



The Ancestry of the Marsupialia. 



In the notice (Nature, December 24, 1908) of Prof. 

 A. A. W. Hubrecht's paper on the early ontogeny of the 

 Mammalia, the writer states that the view adopted by 

 Prof. Hubrecht, according to which the Metatheria are 

 the descendants of placental ancestors, is in direct opposi- 

 tion to my own. May I be permitted to correct this 

 statement, and to point out that it is just this view 

 which I have all along advocated, and still hold? As a 

 matter of fact, the idea that the Metatheria and Eutheria 

 mav best be regarded as the divergent branches of an 

 ancestral placental stock was first definitely expressed in 

 a joint paper by Prof. J. T. Wilson and myself (Quart. 

 Tourn. Micros. Sc, vol. xxxix., p. 579). 



Jas. p. Hill. 



The Zoological Laboratory, University College, 

 W.C, March 24, 



I take Prof. Hubrecht to mean that the Didelphia (Meta- 

 theria) are descended from Eutheria, which is what Prof. 

 Hill, in his own letter, refuses to admit. 



The Writer of the Note. 



