404 



NA TURE 



[March 23, 1876 



trachytes " have not yet been found in these islands, but 

 that the predominant felspathic constituent of the more 

 acid rocks is always plagioclastic. Hence they are 

 described under the names of Andesite, Trachy-dolerite, 

 and Trachy-diorite. The first of these would appear, 

 from the definition given, to correspond with the well- 

 known lavas of Hungary, the last to resemble the green- 

 stone trachytes or " propylites " of the same country. 

 These trachytic rocks are found to assume at times a 

 vitreous character, thus passing into obsidian ; and they 

 occasionally exhibit the perlite modification of structure. 

 The basaltic rocks, noticed by the author, do not appear 

 to offer any features of special interest. 



La Biologic. By Dr. Charles Lelourneau. Bibliothique 

 des Sciences Contemporaines. (Paris : C. Reinwald et 

 O^., 1876.) 

 This small work within five hundred and fifty pages 

 gives a concise description, in a popular form, of the 

 phenomena exhibited by living organisms. " C'est une 

 oeuvre de vulgarisation," intended for the commencing 

 student and the amateur. Such being the case many im- 

 portant facts have to be omitted, and much has to be 

 embodied in a general form. As in most works many of 

 the broad statements arc apt to mislead. It is all very 

 well to say, as does Dr. Letourneau, that the heart is 

 trilocular in the reptiles and quadrilocular in birds, but 

 considering the nature of that organ in the crocodiles, we 

 think its nature in them ought to be mentioned. The 

 title of the work is so all-embracing that v/e think it can 

 hardly be justified by its contents. Morphology as well 

 as physiology, together with the principles of evolution 

 and classification, are all parts of " biology," nevertheless 

 in the work before us morphology, and the immediate 

 dependents of that science, are not touched upon. A 

 more fitting title would have been " Comparative Physi- 

 ology, Vegetable, and Animal." Several illustrations are 

 introduced, and these are well selected, most if not all 

 from other works. The descriptions are clear and con- 

 cise, many too short to be of much service except as a 

 first-book. 



Algebra for Beginners. By James Loudon, M.A., Pro- 

 fessor of Mathematics and Natural Philosophy, Uni- 

 versity College, Toronto. (Toronto, 1876.) 



This work is an elementary one, taking the usual subjects 

 up to and including Quadratic Equations. There is a 

 chapter on Exponential Notation, giving a fair exposition 

 of the Theory of Indices. There is nothing noteworthy 

 in the execution : it is quite on a par with many similar 

 text-books in this country, so that the chief point of in- 

 terest is the information it gives us as to what instruction 

 is given in the subject to the rising generation in Canada. 

 The use of mononomial strikes us as being affected. The 

 work is exceedingly correctly printed. There are but six 

 mistakes, we think, in the whole book, three of which 

 are in the answers (xv. 3, xxxvii. 14, li. 16). Many of 

 the questions are traceable to English sources. 



LETTERS TO THE EDITOR 



[The Editor does not Itold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications.'] 



Coloured Solar Halos 

 In his interesting scientific notes taken in the Himalayas, 

 and printed in the last number of Nature (p. 393), Dr. Arthur 

 Schuster mentions the frequency of the occurrence, in India, of 

 rainbow-coloured rings round the sun, and states that he has 

 only once seen this phenomenon in England. The apparition 

 of a complete iridescent circle is no doubt rarely seen, but I have, 

 since the winter of 1873-74, when I first observed them, so fre- 

 quently seen fragments of such rings both in Switzerland and in 



England, that their non-occurrence, when thin white clouds are 

 near the sun, seems to me to be the exception rather than the 

 rule. In this country, and generally at low elevations, they are 

 not easily detected by the unassisted eye, but in the high Alps 

 both in summer and winter I have rarely failed to see them, 

 when the sun and a thin white cloud were at the necessary dis- 

 tance from each other ; they are, however, much more easily 

 observed when the eye is protected from the glare by the neutral 

 tinted glass which is freq uently used for snow spectacles. The first 

 and most vivid iridescent halo I ever saw, appeared projecting 

 from the side of a mountain from behind which the sun was about 

 to ri^e, near the summit of the Fluela pass, and about 7,000 feet 

 above the sea. This was in the winter of 1873-74, and the ther- 

 mometer stood at 19" Fahr. Last August and the first half of 

 September I saw them almost daily on the Riffelberg and at 

 Pontresina, and I have repeatedly noticed fragments of iridescent 

 rings during the past autumn and winter in crossing Kensington 

 Gardens about 9.30 A.M. In London, however, the blue and 

 green rays are rarely visible, owing no doubt to their absorption 

 by the murky atmosphere, whilst the orange and red rays easily 

 reach the eye. On Sunday last, with snow upon the ground, I 

 saw, through neutral tinted glass, the orange and red of the 

 halo as the thin edges of clouds approached, or receded from 

 the sun, and on Monday I distinctly saw the green also. 



I hold these coloured halos to be a decisive proof of the frozen 

 condition of the clouds in which they appear ; firstly, because the 

 cloud seen on the Fluela pass, when the thermometer was 13" 

 below the freezing point, must have been frozen ; and secondly, 

 because I have repeatedly seen a portion, at least, of the lower 

 half of the iridescent circle in the high valleys of Switzerland by 

 looking along a field of snow sloping upwards towards the sun, 

 and when the thermometer indicated temperatures varying from 

 - 1 5° -5 Fahr. to + 23° Fahr. 



It would be worth while to have the occurrence or non-occur- 

 rence of these halos daily recorded in our meteorological obser- 

 vatories, as indications of the temperature of the air at great 

 altitudes. E. Frankland 



On the Evidences of Ancient Glaciers in Central 

 France 



In Nature, vol. xiii. p. 31, Dr. J. D. Hooker gives 

 some notes of traces of ancient glaciers in Central France, 

 especially in the Mont Dore, and in a following short letter (p. 

 149 of the same volume), in reference to this notice of Dr. 

 Hooker, the late Mi. G. Poulett Scrope, the celebrated de- 

 scriber of the volcanic regions of that country, calls in question 

 the exactness of Dr. Hooker's observations. Dr. Hooker in 

 a subsequent letter (p. 166) insists upon the correctness of his 

 views, which he seems to believe original and never before 

 advanced. Neither Dr. Hooker nor Mr. Poulett Scrope seem 

 to have known that I hSve already, in a paper published in the 

 Ausland (1872, Nos. 20 and 21, pp. 460 and 512) entitled, 

 "Erosions und Glctscher wirkungen im Mont Dore, &c." de- 

 scribed the traces of glaciers to a still greater extent than even 

 Dr. Hooker does. Not only did I name the place in question 

 (which is situated just at the entry of the Gorge d'Enfer, upper 

 valley of Mont Dore) and describe it as .an ancient frontal mo- 

 raine of a glacier, but I have also given the view of the late Prof. 

 Lecoq (who was never an Abbe as Mr. Poulett Scrope seemed 

 to believe), who says in reference to this locality, that if ever a 

 glacier had existed m Mont Dore it must have been in this vailey. 

 But besides this point, which in itself is decisive, I noticed a 

 great number of other localities affording examples of polished 

 rocks, transported and rounded blocks, stone lines, and other 

 evident traces of glaciers, which I will not re-enumerate, as they 

 may be found in my above-mentioned paper. 



It is quite clear that Mr. Poulett Scrope was in the wrong in 

 denying that those signs in the Mont Dore are the effects of 

 glacial action, but on the other hand, I must, in justice to 

 myself, courteously remind Dr. Hooker that I have the priority 

 in describing those marks as glacial traces which Lecoq interpreted 

 as water-flood traces. I may say in conclusion that this learned 

 geologist of Central France (Lecoq) personally turned my atten- 

 tion to those phenomena while visiting the Auvergne in 1867, 

 and seemed inclined to accept my interpretation. 



Breslau University, Prussia, March 10 A. von Lasaulx 



The Uintatherium 

 In the abstract of my lecture published in Nature, vol. xiii., 

 p. 387, it is stated that " the first discovered evidences of the 



