4IO 



NA TURE 



{March 3, i5 



The means of thirty-eiijht^ stcxtioas since 1876 give similar 

 results, viz. : — 



1876 i377 1878 



68°-2 ... 6S°-S ... 68°-3 



For 1879 and 1880 the figures have not yet been all worl<ed up, 



but as far as they have been reduced they indicate that the 



intensity of solar radiation was a good deal less than in 1S78. 



Allahabad, February 3 S. A. liiLL 



The Continents alvsrays Continents 

 Mr. Wallace, in his recent excellent vpork on " Island Life," 

 places me in a wrong relation to the question as to the c jntinents 

 having always been continents, After sustaining the view at 

 length in Chapter VI. of his «orl<, without any reference to my 

 arguments on the subject, he later, in Chapter IX., says that "it 

 appears to be the general opinion of geologists \su\ that the great 

 continents have undergone a process of development from earlier 

 to later time^," and then quotes a paragraph of mine by way of 

 proof 



My first discussion of the subject was published in the American 

 Journal of Science for 1846 (vol. ii. of second ser. p. 352), where 

 the " opinion " is partly speculative, the o,-igin of the continents 

 being made one of the initial results of the earth's refrigeration ; 

 but it is not left without the mention of facts sustaining it derived 

 from the actual geological progress of the American c jntinent. 

 In the following volume, in an article entitled " On the Origin of 

 Continents," the view is presented at more length, with some 

 additional confirmatory facts connected with the structure of the 

 continent ; and facts from the e >rth at large bearing the sanie 

 way are brought out in a second paper, " On the Origin of the 

 Grand Outline Features of the Earth." In my "Geological 

 Report " (published in 1849) of the Wilkes Exploring Expedition 

 around the World, in which the same views are briefly presented 

 (p. 431), I argue against "the existence of a continent in the 

 Pacific Ocean within any of the nnre recent geological epochs " 

 [referring here to those of the Tertiary and Quaternary], on the 

 ground of "the absence of all native quadrupeds from its 

 islands, and even from New Zealand." 



A few years later (in 1856) I published, in vol. xxii. of the 

 American Journal, X.\so x&^ex^-axAtx the titles "On American 

 Geological History " and " On the Plan of Development in the 

 Geological History of North America," and in then I gave 

 what I have regarded as a geological demonstration of the view 

 by stating with some detail the facts with respect to the succes- 

 sively-developed features and geological formations of the 

 American continent. Again, in my " Manual of Geology," the 

 first edition (that of 1S63), the progress of the rocks and moun- 

 tains of the continent is traced out, from the V-shaped .\rchcean 

 (Azoic) nucleus, in British America, onward ; and in the account 

 of the Archajan the statement is made (p. 136) that the structure 

 lines apparent over the continent at the close of Archwan time 

 were " features that were never afterwards effaced; instead of 

 this, they were manifested in every new step in the progress of 

 the continent " ; and in the edition of the Manual of 1874, after a 

 fuller account of the positions of Archaean mountains, it is then 

 added (p. 160) : "Hence, in the very inception of the cmtinent, 

 not only was its general topography foreshadowed, but its main 

 mountain chains appear to have been beguu, and its great inter- 

 mediate basins to have been defined — the basin of New England 

 and New Brunswick on the east ; that between the Appalachians 

 and the Rocky Mountains over the great continental interior ; 

 that of Hudson's Bay, between the arms of the northern V. 

 The evolution of the grand structure-lines of the continent was 

 hence early commenced, and the system thus initiated was the 

 system to the end. Here is one strong reason for concluding 

 that the continents have always been continents ; that, while 

 portions may have at times 'oeen submerged some thousan Is of 

 feet, the continents have never changed places with the oceans. 

 Tracing out the development of the American continent from 

 these Archaean beginnings is one of the main purposes of geo- 

 logical hii-tory." In the course of the following pages (nearly 

 400) on Hi^torical Geologv in both editions, the evidence on 

 this point is variously set forth— evidence afforded by the limits 

 of the successive geological formations, by the occurrence of 

 beds of shallow-water deposition at many levels in the long 

 series, and by the progressive origin of the mountain-ranges. 

 Then, in the edition of 1874 (and also that of 18S0) I brmg in 

 (p. 525) the paragraph which Mr. Wallace cites in his Chapter 

 IX. (p. 196)— not as the expression of an "opinion," but a, the 

 summing up after a demon-tration. 



The view that the continents have always been continents, 

 which I have held for forty years, is written so plainly in the 

 geology of North America that I am sure it would never have 

 been set dowai am )ng speculations, even by the most exacting 

 of British geologists, had attentio 1 been fairly given to American 

 facts. If the truth is not taught by British rocks, it is because 

 these repre-ent only a narrow margin of a continent, and hence 

 could not be expected to illustrate general continental develop- 

 ment, hardly more than an animal's leg, however profoundly 

 studied, the embryological laws of the species. 



James D. Dana 



New Haven, Connecticut, February 8 



The Aurora^of January 31 ; Position of Auroral Rays 



The bright loop sho«n in G. F. .Seabroke's drawings of the 

 aurora on January 31 at 6.30 and 6.35 p.m., as seen at Rugby, 

 remind me of a striking feature seen here. If it was the same, 

 a comparison of the observations will give some idea of the 

 height of the phenomenon. As seen here at about 6.24^ this 

 feature was the most conspicuous part of the aurora ; it was a 

 somewhat pear-shaped bright patch, with a region along the 

 middle of it not quite so bright. Its edge was 10° above the 

 moon, at Venus, Jupiter, and rj Pegasi ; its pointed end being 

 low down, and a good deal further to the right. At 6.26.^ Venus 

 was ill the midst of its left end, and Jupiter quite outside. The 

 moon was 5° belo.v the lower edge. The I'usky region gradually 

 darkened, and finally opened through the right end of the patch, 

 which became united by a rather serpentine bright band to a 

 somewhat similar, but partly red, bright patch rising up in the 

 east-north-east. Thi? bright band formed the southern border 

 of the aurora. At 6.31J the position of the central line of this 

 band, including the western bright patch which now formed a 

 loop in it open to the north, was about as fallows : — At or near 

 the moon, one-third of the w.iy from 1 Get i to Venus, fCygni 

 (the junction of the patch with the new band), a Pegasi 1 think, 

 3 Trianguli, a Tauri, and below Procyon. 



The moti in of these features, as well as of all the large masses 

 of the aurora throughout the evening, was approximotely from 

 east to west (magnetic), S3 far as I could ob.-erve. Ihe four or 

 more arches seen at Rugby by G. M. Seabroke at 6.35 were tiot 

 seen by me. 



The spectrum of this aurora was very similar to those of 

 February 4, 1S74, and October 4, 1S74, as given in Capron's 

 " Aurorae," Plate V. ; the band marked 4 of the former being 

 sometimes present and sometines absent. I also saw traces of 

 the red line at times. 



I am surprised that Prof. S. P. Thompson (Nature, vol. xxiii. 

 p. 2S9) is not aware that it is a thoroughly ascertained fact that 

 the rays of auroras lie in the direction of the magnetic dip. I 

 may add that the flashes or pulsations also generally appear to 

 move away from the earth in the direction of the magnetic dip. 



Sunderland, February 24 T. W. Bacichouse 



Auroric Light 



As Mr. W. H. Preece records the magnetic storms, if not too 

 much trouble would he record what took place on the night 

 of January 16 ? — as at midnight there was all the appearance of a 

 grand display; but as the windows were all frost-masked, and 

 my only place of observation was exposed to a cutting wind that 

 would have " shaved a cast-iron police]7;an," to quote Punch, I 

 could not observe what took place. I should also like to know 

 why the grand displays this winter are of white lights. Those I 

 saw in previous years — the best being while stationed in West 

 Gal way between 1S67 to 1872 — were principally red lights, some of 

 them being most brilliant between midnight and morning, while 

 all of them this year have been best early in the night, all lights 

 usually disappearing before or a little after eleven. I am used 

 to white lights in the summer months, but I never before saw 

 them so prominent in llie winter riionths — main lights, cross 

 lights, and glows being white ; while usually, each respectively 

 have different colours. I have not seen an aurora that changes 

 so much in character as the last, except that of September, 1867 

 or 1868 (I think, but I have not my notes to give the exact year). 

 That of 1S67 or 186S was a grand display, rising in a red mass 

 to the zenith, and then shooting out pencils of red, green, white, 

 purple, and orange lights. G. H. KiNAHAN 



Ovoca, February 20 



