April 9, 1908] 



NA TURE 



535 



This makes the number of months in the year thirteen ; 

 but it has this advantage over Mr. I'earce's scheme, that 

 not only are the months all of the same length, but that 

 they all begin on the same day of the week, and thus 

 any given day of the month is on the same day of the 

 week in every month. 



The seven-day week, which is no doubt descended from 

 the Jewish week, is one of the most widely spread institu- 

 tions in the world. All Christian and all Mohammedan 

 nations, although they may agree in little else, agree in 

 respecting the week : and it would be impossible to induce 

 many of them to interrupt the continuity of their weeks 

 by excluding one day annually from any week and two 

 days every fourth year, and unless the change were inter- 

 national and all but universal it would only introduce 

 confusion and destroy that identity of the week which 

 now obtains throughout Christendom and Mohammedom. 



D. Mackie. 



4 Polmuir Road, .\berdeen, March 28. 



Helium in the Atmosphere. 



Recent investigations have demonstrated the widespread 

 presence of the inert gases in the crystalline rocks, and the 

 Hon. R. J. Strutt has shown that while the bulk of the 

 gases in granite consists of nitrogen, there is a small but 

 appreciable quantity of argon and helium, the former 

 amounting to from three to four times the latter. On the 

 disintegration of the rocks a portion of these must find 

 their way into the atmosphere. The question arises 

 whether our present atmosphere contains the accumulations 

 of past accessions from the earth's crust, in the same way 

 as the sodium chloride in the sea represents, subject to 

 certain qualifications, the sum of the contributions of the 

 rivers in the past. 



It is found, however, that while the air examined in 

 our laboratories contains about i per cent, of argon, there 

 are only one or two parts in a million of helium. The 

 small proportion of the latter has given rise to the sugges- 

 tion that it is escaping from the atmosphere as fast as it 

 enters it. This receives no support from the kinetic theory 

 of gases. Dr. G. H. Bryan calculates (Phil. Trans., A, 

 cxcvi., p. 19) that at a temperature of 127° C. it would take 

 eighty-four thousand million years to remove a layer 

 I centimetre thick of helium from the surface of the earth. 

 In other words, the pressure of the gas which at the 

 beginning of that period was found at the height of a 

 centimetre would at its end, other conditions remaining 

 the same, be found at the surface of the earth. 



Dr. Johnstone Stoney, however, supposes that there may 

 be extraordinary molecular velocities, due to collisions and 

 other causes, which result in the loss of helium. Such 

 an hypothesis, however, is quite unnecessary, for, accord- 

 ing to the ordinary views as to the constitution of gases, 

 thev will not distribute themselves uniformly in the atmo- 

 sphere, but to a certain extent take up positions according 

 to their relative densities. Mr. J. H. Jeans (" Dynamical 

 Theorv of Gases," 1904, p. 316) calculates that if helium 

 forms a millionth part by volume of the air at sea-level, it 

 must amount to more than 2 per cent, at an altitude, which 

 is dependent on temperature. With our increasing know- 

 ledge of atmospheric temperature and the distribution of 

 helium in the earth's crust, we ought soon to be in a 

 position to calculate the present amount of free helium, and 

 employ it to obtain an approximate higher limit for the 

 total disintegration of crystalline rocks since the consolida- 

 tion of the earth's crust.' J. W. Ev.tNS. 



April Meteors. 



MooN'LiGHT will prove a serious impediment to observa- 

 tions of the Lyrids in the present year, the more especially 

 as, according to calculations made by the writer, the 

 general maximum of these meteors will take place immedi- 

 ately after full moon. The following are particulars as to 

 when meteor showers at this period may be expected to 

 make their appearance, and the computed intensity of the 

 display in each instance, the results being expressed in 

 Greenwich Mean Time : — • 



Epoch, April iS. Shower of second order of magnitude; 



NO. .?006, VOL. Ti^ 



the maxima precede the epoch, the principal of which 

 occur on April 16, 6h. 25m. ; April 16, I4h. ; and April 17, 

 6h. som. 



Epoch, April i8, ijh. This shower is of the twenty- 

 second order of magnitude, and has its principal maxima 

 on April 16, 7h. 45m. ; April 16, gh. 40m. ; and April 17, 

 I3h. This minor shower has also two secondary maxima, 

 occurring on .'\pril 17, 23h., and April 18, 3h., re- 

 spectively. 



Epoch, April 21. This shower is of the twenty-first . 

 order of magnitude, its principal maxima, which precede 

 the epoch, occurring on April 19, i6h. 35m. ; April 19, 

 igh. 20m. ; and April 20, 1711. 



Towards the end of April there is another meteor shower 

 of the ninth ' order of magnitude, the epoch of which 

 occurs on April 29, 6h., and the principal maxima of which 

 fall on April 27, ibh. ; April 27, igh. 30m. ; and 

 April 27, 2ih. 



As a general rule, the intensity of a meteoric display is 

 inversely as its estimated order of magnitude ; hence 

 meteors may be expected to be most abundant on the 

 night of April 16, as the two strongest maxima of a shower 

 of the second order of magnitude occur on this date, besides 

 two maxima of another shower which is partly super- 

 imposed on the former. Lyrids will probably be most in 

 evidence on the morning of .^pril 17. 



Dublin. John R. Henry. 



Coloration of Glass and Quartz by Radium. 



On many occasions attention has been directed to the 

 coloration of glass and quartz by the rays from radium. 

 The coloration of glass is generally connected with the 

 presence of manganese or lead, and I venture to suggest 

 that in quartz too the darkening arises from the associa- 

 tion of some foreign substance with the silica. 



A small plate of quartz crystal was exposed to radium 

 for three weeks, and became, not only irregularly violet 

 at one place, but also showed two sharply defined parallel 

 lines strongly coloured, with the space between them 

 scarcely affected. On the other hand, a quantity of 

 powdered chemically pure silica acquired no colour after 

 the same exposure. It may also be pointed out that pure 

 boric acid, fused to a transparent plate and protected from 

 moisture, was unaffected by radium even after two months' 

 continuous exposure tp the rays. 



Borax, however, will show a slight action after three 

 weeks, and both these substances afford, when incorporated 

 with a small quantity of pure sodium silicate, a good 

 basis for the production of experimental glasses to test the 

 action of radium when other constituents, such as lead, 

 ii'on, &c., are added either singly or together. 



It may be found that the coloration by radium will 

 serve as a test for the purity of the silica used in making 

 vessels for certain classes of chemical research, so that, 

 apart from its physical interest, the matter seems worth 

 following up. Ch.hrles E. S. Phillips. 



Castle House, Shooters Hill, Kent, April 2. 



An Early Notice of Neolithic Implements. 



The subjoined quotation must, I think, be among the 

 earliest specific descriptions of a Neolithic implement found 

 in this country. 



Newbery's " A Compendious History of the World " 

 (vol. i., London, 1768, pp. 11-12) : — "That the earth has 

 been amazingly altered since its first formation is evident 

 from the spoils of the sea being daily discovered even in 

 the midst of rocks and the tops of mountains : to which 

 let me add that the skeletons, horns, &c., of the animals 

 of one country, have been dug out of the bogs and mines 

 of another, even at an immense distance, and where suth 

 animals are not now to be found : even stones have been 

 discovered at a great distance in the earth, which bore 

 evident marks of art about them ; and some time since I 

 had two taken out of a peat pit near Newbury in Berks, 

 which were large, ground to an edge in the form of an 

 ax, and so perfect that wood might be cut with them." 



John L. Myres. 



The University of Liverpool, March 23. 



