NATURE 



[September 12, 1912 



It is true that one may see flints emerging from 

 arctic glaciers unscratched and unrounded, while softer 

 rocks are reduced to strongly striated boulders ; but 

 Dr. Irving seems to conceive the Boulder Clay as 

 something distinct from the ice-sheet in which it 

 originated, and as merely pressed on by superincum- 

 bent ice. It cannot be too strongly urged that the 

 lower portions of glaciers ot the continental or ice- 

 sheet type consist largely of stones and mud and 

 abrading sand-grains, and that these materials are 

 held in the grip of the ice and are moved against one 

 another as it flows. The ice-sheet is, in fact, a con- 

 glomerate with an ice cement; the Boulder Clay is an 

 essential part of it, and remains as its representative 

 when the portion that can melt has yielded before 

 climatic change. Gren'ville A. J. Cole. 



Roval College of Science, Dublin, September 6. 



Boulder Clay in Essex. 



YoLR correspondent Dr. Irving, in his letter en- 

 titled "Boulder Clay in Essex" (Nature, .August 22), 

 states that he has made a keen but futile search for 

 a human artefact in the Boulder Clav, and, I presume, 

 infers that these relics do not occur therein. 



I have had no opportunity of carefully examining 

 the Boulder Clay of Essex, but for the last six years 

 I have been. able to search that of Suffolk, and know 

 that the occurrence of humanly flaked flints in this 

 latter deposit is capable of unassailable demonstra- 

 tion. .As until the notification of a human skeleton 

 having been found beneath the Boulder Clay no 

 search had been made in the clay for worked flints, and 

 as that notification was rhade only a few months ago, 

 I think that perhaps further and more prolonged 

 search in the Essex deposits will reveal some of the 

 type of implements which are found in Suffolk. 



But even if this is not so, it cannot be brought as 

 an argument against man's presence here before the 

 deposition of the Boulder Clay. It would be as foolish 

 to argue that because palaeolithic implements are not 

 found in a certain section of river-gravel, they do not 

 occur in any, other portion of the same deposit. 



J. Reid Moir. 



12 St. Edmund's Road, Ipswich. 



The "Titanic." 



A'ofR article (Nature, .August 2q. 1912) on the 

 report of the .Advisory Committee having emphasised 

 the contention from the first of some of us (students 

 of science and old naval commanders) as to the in- 

 sanity of high speed "at night in the known vicinity 

 of ice," it behoves sUrely men of science to ask the 

 question whether we have not reached the imperative 

 limits of that false security which the "practical 

 man " is wont to feel in his contempt for scientific 

 "theory"; and, further, whether the time has not 

 therefore come for legislation requiring commanders 

 of the largest ocean-going steamers to hold a diploma, 

 guaranteeing such a systematic course of studv (say in 

 a class at Greenwich or Kensington) in marine phvsio- 

 g-raphy and the elementary laws of mechanics as 

 woulil quicken their imagination as to the uncer- 

 t.iinty and the magnitude of the risks to be run in 

 .111 abnormally ice-drifted sea. Lord Mersev's report 

 may whitewash the facts, but the facts en evidence 

 remain ; and the chain of cause and effect in the 

 lamentable and tragic loss of the Titanic leads us in 

 the last resort to the notorious contempt for scientific 

 acquaintance with the facts and laws of nature on the 

 part of the "practical man." .X. 1r\i\(,. 



Ilockerill, Bishop's Stortford, September 2. 

 NO. 2237, VOL. 90] 



STUDIES OF AURORA.^ 



ONE or two photographs of aurora seem to have 

 been taken before, but Prof. Stormer is the 

 first to meet with marked success. In the earlier 

 of the volumes before us he describes with full 

 detail the apparatus and methods employed in 

 photographing aurora during a stay of some months 

 at Bossekop, in the extreme north of Norway, early 

 in 1910. Photographs were taken by Stormer and 

 an assistant from the two ends of a base of about 

 4J kilometres, simultaneity of exposure being 

 secured by telephonic signal. Using special plates, 

 satisfactory photographs were obtained with a few 

 seconds' exposure. One or more prominent stars 

 were always included in the photograph, and the 

 time was carefully noted. From the known co- 

 ordinates of the stars, it was thus possible to fix 

 the position of the aurora. The base was long 

 enough in general to give a parallax which could 

 be measured with sufficient accuracy to determine 

 the approximate position and height of selected 

 prominent points. The heights calculated for the 

 different auroras varied from 36 to 461 kilometres. 

 Fig. I shows a photograph — from the original 



of a. photograph of ; 

 riglnal size.; 



negative — taken with 3 seconds' exposure ; Fig. 2 

 is an enlargement, the original of which had a 

 5 seconds' exposure. 



The second of the two volumes referred to 

 below repeats some of the information given in 

 the first, but is mainly theoretical. Stormer was 

 apparently first attracted to the subject of aurora 

 and magnetic storms by the work of his well- 

 known colleague at Christiania, Prof. Kr. Birke- 

 land, but the views he now holds arc independent. 



An electrified particle projected in a uniform 

 magnetic field IT describes with uniform velocity a 

 helix about the lines of magnetic force. If pro- 

 jected perpendicular to the lines of force, it de- 

 scribes a circle of radius p. If in be the mass, e 

 the charge, v the velocity of the particle, and V 

 the velocity of light, then, according to Stormer, 

 Hp = {ni/e)v{i-v"/l"~)-K This differs from the 

 usual formula in English books unless (I'/Vf be 



* " Bericht iiber eine Expedition nach Bossekop zwecks photographischer 

 Aufnahmen und HOhenmessuneen von Nordlichtern. By Carl Stormer. 

 (Utgit for Kridtjof Nansens Fond.) Pp. iii-^SS plates. (Kristiania: 

 Jacob Dybwad, 1911.) E.vlract from Videnskap. Skrifl. Mat. Natur. Klasse. 

 igii 



" .Stir les Trajectoires des Corpuscles electrises dans I'esp.-ire sous I'action 

 du Magn^lisme Terrestre avec application aux Aurores bore'ales (seconcj 

 Mimoire). By Carl Stormer. Pp. 163+10 plates. Extrait des Archives, 

 des Sciences physiques et naturelles, Geneva, 1912. 



