November i6, 191 i] 



NATURE 



mass, gaseous matters which are given off when the 

 rock is heated. This is especially true of lavas of a 

 glassy character, which when fused have been shown 

 to swell up into masses of pumice of many times the 

 dimensions of the glass from which it is formed. M. 

 Albert Brun, of Geneva, has collected and analysed 

 the gases given off in such cases, and finds them to 

 be nitrogen, ammonia, chlorine, hydrochloric acid, 

 carbonic acid, and various hydrocarbons. Reasoning 

 from these and other observations, he has been led 

 to the conclusion that steam, instead of playing the 

 most important part in volcanic eruptions, must be 

 regarded, in many cases at least, as only an adventi- 

 tious and accidental accompaniment of them. He has 

 certainly shown grounds for the more thorough in- 

 vestigation of the nature and composition of these 

 mixed gases, which, as recent studies have shown, 

 play such an all-important part in volcanic outbursts. 

 But in addition to the more exact and systematic 

 studies which have been made of the great volcanic 

 eiuptions in recent years, there is another class of 

 researches which have supplied evidence of at least 

 equal value concerning the nature and origin of these 

 phenomena. 



The study of rocks in thin sections under the micro- 

 scope has shown that the two classes of rocks known 

 as "'plutonic" and "volcanic" respectively are essen- 

 tially identical, and pass into one another by in- 

 sensible gradations. Great areas of crystalline rocks 

 ("batholites ") and lake-like intrusions of similar 

 materials (" laccolites "), lying in the midst of sedi- 

 mentary and other rocks, were probably the roots of 

 the volcanoes of previous periods in the earth's his- 

 tory. In these cooled reservoirs v^-e may study the 

 changes which have taken place in the magmas that 

 have supplied the old volcanic vents, and — inverting 

 the Lvellian principle — we may reason concerning the 

 processes which must now be going on beneath exist- 

 ing volcanic vents from what we can prove to have 

 taken place beneath those of former geological 

 periods. Nor are there wanting examples of ancient 

 volcanoes, dissected by the scalpel of denudation, 

 which illustrate the intimate connection which exists 

 between the plutonic and volcanic rock-masses. 



The author of the memoir before us is well known 

 to geologists by a number of valuable memoirs deal- 

 ing with the evidence of changes which must have 

 taken place in the great underground reservoirs of 

 igneous rocks. These he has had the opportunities of 

 i investigating while engaged as a Canadian member 

 of the International Boundary Surveys. More re- 

 \ cently, he has had the opportunity of making a 

 ') detailed investigation of the phenomena exhibited in 

 ij the Hawaiian volcanoes. His outline of "a general 

 ; working theory of vulcanism " is the result, as he tells 

 i us, "of the writer's studies in the Hawaiian Islands 

 in 1909, but many of the chief conclusions are 

 founded on his field-work in plutonic geology, as well 

 \ as on the geology of many ancient volcanic forma- 

 tions." 



I That the hypotheses he now formulates arc of a 

 I somewhat speculative character, and that many of 

 his conclusions are more or less tentative, Mr. Daly 

 fully admits; but that, nevertheless, his memoir is an 

 important contribution towards the solution of a very 

 difficult problem everyone will agree. He summarises 

 his suggestions as a " substratum-injection hypo- 

 thesis," believing that the surface phenomena can 

 best bo accounted for by abyssal injections of a deep- 

 seated basaltic magma through an acid substratum of 

 granitic or gneissic rocks everywhere underlying the 



f\ sedimentary formations. But in elaborating his 

 . theory the author is led into a numb<>r of discussions 



NO. 2194, VOL. 88] 



of points of extreme interest and importance, and, 

 even if his main conclusions are rejected, these sub- 

 sidiary discussions retain their suggestiveness and 

 value. 



It is admitted by the author that the conditions 

 leading to his "abyssal injections" "form a subject of 

 great theoretical difficulty " ; he apparently accepts 

 the view that the high temperatures underground are 

 j due to the earth being a cooling globe, although he 

 ! admits the influence of various chemical reactions in 

 i augmenting, locally, these high temperatures. The 

 \ chief argument in favour of the view that the earth's 

 j interior is in a highly heated, if not molten, condi- 

 i tion is, of course, derived from the fact that obser- 

 I vations made in mines, tunnels, wells, and bore-holes 

 everywhere indicate a progressive rise in tempera- 

 ture as we go downwards. Nevertheless, the most 

 recent observations of underground temperatures have 

 revealed such startling discrepancies between the re- 

 sults obtained in different areas — discrepancies that, it 

 seems, are quite incapable of being explained by 

 differences in the conductivity of rocks and similar 

 causes — that the argument for a "molten globe" 

 based on underground temperatures loses much of its 

 force, and with it must go the estimates of the earth's 

 age that have been based upon it. In these cir- 

 cumstances, the thoughts of geologists turn, not un- 

 naturally, to the great revelation of radio-activity as a 

 source of heat, for here may possibly be found the 

 means of removing, to some extent at least, the 

 " theoretical difficulties " which, the author admits, 

 still beset the explanation of those deep-seated actions 

 for which he argues. J. W. J. 



SPANISH OBSERVATIONS OF BROOKS'S 

 COMET (191 It). 



D ROOKS'S comet has recently been a conspicuous 

 -*-' object, and no doubt a great number of valuable 

 observations have been made, both photographically 

 and visually, at most of the observatories in the 

 northern hemisphere. 



Some very interesting records have recently beer* 

 received from Sefior F. Iniguez, the director of the 

 Madrid Observatory, and not only do these include 

 photographs of the comet itself, but an excellent 

 spectrum accomnanied by a list of the wave-lengths 

 of the bands recorded. 



The photograph showing the form of the comet was 

 secured on September 28, with a 6-inch Grubb doublet, 

 during an exposure of one and a quarter hours 

 (gh. 15m. to loh. 30m.), the comet then being of the 

 second or third magnitude. This photograph is re- 

 produced here (Fig. i), the scale being i tnm. to 5 

 minutes of arc. On this date the tail stretched to a 

 distance of 15 degrees, and consisted of delicately fine 

 interlacing filaments ; the nucleus with its surrounding 

 nebulosity measured 21 minutes in diameter. Spectro- 

 scopic observations were made visually with a slit 

 spectroscope, and photographs were secured with the 

 Grubb photographic equatorial, having an objective 

 prism of 20 cm. aperture and 20° refracting angle. 

 These have shown the spectrum to consist of seven 

 images of the nucleus. The visible bands are the 

 three situated at the red end of the spectrum, and 

 these form three distinct spectral bands, while the 

 sixth is composed of fine lines. The seventh appears 

 double, although its components are not well defined 

 and were measured as single. 



The wave-lengths have been determined by Sefior 

 Iniguez from four plates taken on September 19, 20, 

 and 26. The three visual monochromatic images of 



