February 3, 19 10] 



NA TURE 



3^.9 



Having recently had occasion to prepare some silicon, 

 precipitated silica was heated with magnesium powder in 

 a Hessian crucible. One quarter gram-molecule of each 

 was employed. The heating had proceeded some little 

 time when suddenly the mixture exploded with terrific 

 violence, shattering the crucible to a powder and sending 

 out a great sheet of white flame. So great was the force 

 of the explosion that the iron ring of the retort stand 

 which held the crucible was bent out of shape. On 

 examination it was found that the ingredients were pure, 

 except that they might not have been quite free from 

 moisture. 



What I wish particularly to point out is that there is 

 not a word in any of the text-books I have referred to of 

 the danger of a very serious explosion in the above pre- 

 paration. 



Perhaps someone can say, definitely, whether the presence 

 of a trace of water will cause such a mixture to explode on 

 heating. F. H. Power. 



Lincoln Grove, Radcliffe-on-Trent, Notts, 

 January 26. 



Intermittent Glow of the Tail of the New Comet. 



In Mr. Rolston's interesting and valuable article on the 

 new comet (Nature, January 27) reference is made to the 

 statement of the Rev. F. J. Jervis-Smith that several 

 persons observing at Lymington on January 22 thought 

 the tail appeared to flash slightly and continuously. 



Now, on the evening of that day I got the impression, on 

 seeing the comet setting in the west-south-west, that there 

 was an intermittent glow of the tail matter, in no very 

 marked degree, it is true, but still there was a seeming 

 perceptibilit)'. 



Later that evening I was told by an unskilled observer 

 that he had seen " faint lights issue from the head and 

 pass up to the end of the tail." 



The Conclusion I came to at the time exactly coincides 

 with that referred to in the article, which is that the 

 appearance was referable to the low position of the object 

 and consequent atmospheric effects. 



The interposition between the observer and the tail of a 

 slight cloud or of some distant mass of smoke, though in 

 itself too filmy to be noticed from afar off against a dark 

 sky, would, doubtless, account for these light changes. 



A correspondent once wrote to me — in some alarm, I 

 thought — that Jupiter had on the previous evening behaved 

 in a manner which was, to say the least, extraordinary, in 

 that it had " kept going in and out " for five minutes on 

 end. As the planet was then low in the sky, I concluded 

 that the effect described by my perturbed correspondent 

 was due to rapidly moving patches of unseen denser vapour 

 than that which surrounded the planet, intruding in the 

 line of sight. .\t the same time, I was far from being 

 unmindful of the way in which Jupiter's light will fre- 

 quently palpitate when the planet is Hearing the horizon. 



J, H. Elgie. 



72 Orange .Avenue, Leeds, January 28. 



Unemployed Laboratory Assistants. 



A NUMBER of lads who have been employed as labora- 

 tory monitors in secondary schools, and whom the London 

 County Council arS unable to retain in their service beyond 

 the age of sixteen years, have been referred to us by the 

 London County Council with the view of our placing them. 

 Some of them we have already been able to place in suit- 

 able employment, but there are still one or two on our 

 books for whom we seek situations. 



They all have an elementary knowledge of physics and 

 chemistry. Some have learned glass-blowing and bend- 

 ing, and one of the applicants has already passed the Board 

 of Education examination in chemistry (Stage L). If any 

 readers of Nature would like to have further particulars 

 of these boys, I should be glad to suppiv them with in- 

 formation. Godfrey Reiss (Hon. Sec>i. 



-Apprenticeship and Skilled Employment Association, 

 •;6 Denison House, 296 Vauxhall Bridge Road, 

 London, S.W., January 31. 



VO. 2IOI, VOL. 82] 



THE AROLLA PINE.i- 

 'X'HE Arve or.AroIla pine is the most beautiful of 

 -•• Alpine conifers. The glossy green of its acicular 

 tufted leaves, the curving cone of its outline, the com- 

 bined strength and grace of its growth, malie it yet 

 more attractive in colour and in form than the darlier 

 and sturdier spruce. It ranges, though rather fitful 

 and sporadic in distribution, throughout the Alpine 

 chain, passing on to the Carpathians, where, however, 

 it does not grow nearly so high above the sea-level, 

 but it is most abundant in north-eastern Asia, which is 

 apparently its birthplace. There it extends northward 

 to the tree-limit, eastward to the Altai, the Sea of 

 Okhotsk, and the north of Japan, and westward even 

 so far as the Lower Dwina. Between the occupants 

 of these two provinces some marked differences exist, 

 so that Dr. Rikli recognises an Arctic and an Alpine 

 subspecies, to the latter of which his memoir is re^ 



Fig. 1.— The Arve in Vuu 



stricted. The Arve is a lover of the mountains, and 

 on these it has a rather wide vertical range. When 

 growing wild it is seldom met with below the 1350- 

 metre contour-line. Dr. Rikli mentions as the lowest 

 instance one at about 1200, near Raron, in the Upper 

 Rhone valley. Its upper limit is about 2400 metres, 

 the highest occurrence on record being 2585 metres, 

 on the Plattje, near Saas Fee. Such cases, however, 

 are exceptional, where the tree obviously has had a 

 hard struggle for existence, and it cannot be said to 

 flourish above 2300 metres. On the Northern range of 

 the Alps, the vertical limits within which it grows 

 freely are narrower than in the Central— or Pennine 

 and Lepontine — range, the difference between them, in 



1 Die Awe in der Schwei?. Ein Beilrac zur Waldge^chichte und Wald- 

 »i7tschaft der Schweizer Alpfn von Dr. M. Rikli. Mit einer Arvenkarte der 

 Schweiz. einer Waldkarte von Davos, ig Specialkarlen in Litho^raphie, 

 9 Tafeln in Lichtdruck und 51 Textbildern. (Neue Denk-schriften der 

 Schweizerischen Naturforsrhenden Gesellschaft, Band xliv.) Pp. .\l+455. 

 (Basel : Georg & Cie. ; Zurich : Ziircher & Furrer, 1909.) 



