Feb. 28, 1884] 



NATURE 



403 



and, so far as it goes, a sound, criticism of certain false or 

 inadequate views of the world. Schopenhauer claimed to 

 be the true follower of Kant, and when he is speaking of 

 " the world as Idea," we find ourselves on the general 

 ground of the modern philosophical criticism which dates 

 from Kant. Schopenhauer certainly neglects much that 

 is valuable in Kant, and presents other elements super- 

 ficially ; but, perhaps for that very reason, he may be 

 useful as a populariser of thoughts which, in one shape or 

 another, it is essential for the modern world to master. 

 We need only note here his insistence on the complete 

 relativity of subject and object — a relativity which, of 

 course, excludes the possibility of any causal relation be- 

 tween them — and his criticism of the ideas of space, time, 

 and matter, leading him to the conclusion that the world 

 of objects exists as a system of complete relativity, in 

 which no individual objects can claim any reality e.xcept 

 what consists in their necessary relation to one another. 

 Any one reading these and similar passages must acknow- 

 ledge that, where his doctrines are otherwise sound, 

 Schopenhauer's clear and incisive style makes him an 

 admirable interpreter. Andrew Seth 



OUR BOOK SHELF 



Cours de Mineralogie. A. De Lapparent. (Paris : 

 Savy, 1883.) 



Mineralogy was the father of Geology ; but the son has 

 for many years in this country shown great want of 

 respect to his parent. A very large proportion of our 

 geologists are e.\traordinariIy ignorant of mineralogy. To 

 them as well as to those who have not so seriously 

 neglected that branch of science we recommend a perusal 

 of the work before us. The object of its distinguished 

 author (who has already rescued French Geology from 

 the charge of possessing no modern text-book of native 

 origin) is in the first place to simplify as much as possible 

 the teaching of rational crystallography, as established by 

 the works of Bravais and completed by Mallard, so as to 

 bring it within the comprehension of all earnest students 

 of minerals and rocks ; and in the second place to put 

 geologists in possession of the knowledge which they must 

 acquire if they would apply themselves with any satisfac- 

 tion and profit to the study of the microscopic structure 

 of rocks. 



The volume is divided into three parts. In the first of 

 \}a.t%t,^wi\^\e.diGcometricCrystaUography, M. De Lapparent 

 states the laws of crystalline symmetry and shows in detail 

 the forms of which each system is composed, these forms 

 being rigorously classed and deduced from each other 

 according to the method of Bravais. Tables and stereo- 

 graphic perspective diagrams are added. 



The second part, or Physical Crystallography, is devoted 

 to the e.Kplanation of the physical, and especially the 

 optical, properties of crystallised matter. It concludes 

 with an analysis of the different crystalline groups, with 

 which, following Mallard, the author connects the phe- 

 nomena of isomorphism and dimorphism. 



The object of the third part is the Description of the 

 Principal Mineral Species. The author adopts a system 

 of classification which is entirely new, and which might 

 be called the geological system of mineralogy, because it 

 is based upon the part which each species plays in the 

 composition of the earth's crust. From this point of 

 view minerals are divided into four great classes: — (i) 

 silicates or elements of the fundamental rocks. (2) 

 Elements of mineral veins. (3) Metallic minerals. (4) 

 Combustible minerals. 



The work consists of 550 pages, with 519 figures 



inserted in the text, a chromolithographed plate, and 

 an index comprising 3500 names, from which a knowledge 

 can be obtained of all terms employed in mineralogy. 



LETTERS TO THE EDITOR 



{The Editor does not hold himselj responsible for opinions expressea 

 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. 



[The Editor urgently requests correspondents to keep their letters 

 as short as possible. The pressure on his space is so great 

 that it is impossible otherwise to insure the appearance even 

 of comihunications containing interesting and novel facts .^ 



The Remarkable Sunsets 



The remarkable and beautiful atmospheric phenomena which 

 within the last four or five months have so powerfully attracted 

 attention in all parts of the world, made their appearance here 

 about the same time that they did in England and on the con- 

 tinent of Europe. It is true that as early as October 14, 1S83, 

 somethiniT similar was noticed at Santa Barbara, abiut 2S0 

 miles south-east of this place ; but the characteristic phenomena 

 were not observed here and at other positions on the coast of 

 California until after the middle of Novemlier, 1SS3. I first 

 observed it on the evening of November 24, when it presented 

 a very striliing appearance. That afternoon the sky had been 

 overcast w ith dark clouds, and the south-east wind had brought 

 a slight rainf,"!!. Towards sunset a bright portion of sky ap- 

 peared at the western horizon, extending to an altitude of about 

 10 , while the dark hood of clouds enveloped the remainder of 

 the celestial vault. At 6 p.m. the lurid redness (almost angry) 

 of the western horizon attracted universal attention ; it had the 

 appearance of a sky illuminated by an immense conflagration. 

 Doubtless the effect was heiijhtened by the contrast with the 

 dark canopy of clouds. Similar appearances, more or less con- 

 spicuous, presented themselves during the remaining days of 

 November, and in a less striking manner (when the weather was 

 favourable) during the month of December, both after sunset 

 and before sunrise. At a quarter past six on the morning of 

 November 29 the eastern sky emitted such a brilliant ruddy 

 light as to arrest my attention by the peculiar red illumination 

 of the window-curtain of my bedroom. On looking out, the 

 whole eastern sky was seen to be drenched in gorgeous red. 

 During the month of January, 1SS4, the "upper-glows" (as 

 Miss Ley appropriately designates them) became much less 

 conspicuous. 



At the period when the phenomena were most conspicuous, 

 the atmosphere during the day was not perfectly clear, although 

 the sunlight was not obscured to any consideralile extent : — there 

 was always observed a thin veil of fleecy clouds covering the 

 heavens, and a whitish glare manifested itself about the sun, 

 extending to a distance of about 20° or 25° from his centre. It 

 is evident that the suspended matter producing these phenomena 

 must have been above the region of the loftiest cirri, for ordinary 

 changes of weather and disturbances in the atmosphere did not 

 modify the appearances. 



But the manifestations presented by the sky seem to have been 

 so nearly identical in all parts of the globe, that detailed descrip- 

 tions of them, as exhibited here, are unnecessary. It was, 

 however, evident that the phenomena were less pronounced on 

 this coast than they were in many other countries. This was 

 indicated by the fact that, wherever the phenomena were suffi- 

 ciently developed, the sun during the day was encircled by more 

 or less distinct coloured halos or corona: ; whereas at this place 

 it amounted to nothing more than a whitish glare about that 

 luminary. The Rev. S. E. Bishop writes me from Honolulu, 

 that the>e chromatic circles around the sun were constantly 

 observed in all of the Hawaiian Islands from September 5 to 

 December 15, 1883 ; and I notice that they were ob^erved in 

 England as frequent accompaniments of the upper-glows. 



While the large size of these coloured circles might (as I have 

 indicated in a letter to Science) seem to connect them with the 

 well-know n ice-crystal halos of 22' radius, yet I am disposed 

 to regard this chromatic feature of the phenomenon as mainly 

 due to the diffractive action of the impalpable dust-particles 

 suspended in the lofty supra-cirri regions of the atmosphere. 

 Nevertheless, inasmuch as the experiments of M. Coulier and 

 Mr. John Aitken show that the presence of dust-particles in the 



