April 28, 1892] 



NATURE 



605 



Handy Atlas of Modern Geography. (London : Edward 



Stanford, 1892.) 

 It would be difficult to obtain a small atlas more com- 

 plete than this. Every place of any importance appears 

 to be represented on one or more of the thirty coloured 

 maps. The degrees of latitude and longitude are sub- 

 divided into parts of five minutes each, so that the 

 positions of places, the names of which are not engraved, 

 can be easily and accurately located by reference to the 

 alphabetical list at the end. This list is a comprehensive 

 one. It gives the latitude and longitude of the principal 

 mountains, rivers, capes, bays, islands, towns, and villages, 

 and forms an excellent supplement to a very good atlas. 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of !>! ATURit. 

 No notice is taken of anonymous communications.^ 



Aurora. 



A VERY brilliant display of aurora was seen here last night, 

 the 25lh inst. At about 9.25 p.m. a number of red streamers 

 proceeded from a length of some 110° in azimuth along the 

 northern horizon, and extended upwards for (on an average) 30°. 

 The length of the streamers varied quickly, sometimes shooting 

 upwards for 70" from the horizon. In the course of five 

 minutes the red streamers gave way to white or yellowish white 

 ones, narrower and more sharply defined than the red ones. 

 At 9.40 p.m. there was a decrease in the brilliancy of the 

 phenomenon, but at 9.45 p.m. long red streamers again 

 appeared for a few minutes, which again shortly gave way to a 

 brightness of the horizon only. Close to the horizon the colour 

 was white, or nearly so, the whole time. The apparent point 

 of convergence of the streamers was far south of the zenith, say 

 30°. Geo. M. Seabroke. 



Temple Observatory, Rugby, April 26. 



Probably many of your readers witnessed the brilliant dis- 

 play of the northern lights between nine and twelve o'clock last 

 night, the 25th, but it may be as well to call attention to it, as 

 being the finest display seen here for many years. Appearing 

 soon after nine o'clock, the luminous arc and the radiating beams, 

 sometimes rose and orange coloured, presented a varied and 

 beautiful spectacle until close upon midnight, when they 

 faded away. 



The most noteworthy features of this display were the vivid- 

 ness and height of the arc, which reached an angle of about 13° 

 above the horizon, whilst the beams were visible up to 51°. The 

 whole expanse of the arc from east to west was about 93°, 

 and the duration of the phenomenon a little under three hours. 



Arthur Marshall. 



Cauldon Place, Long Row, Nottingham. 



A fairly distinct aurora was visible here on the northern 

 horizon last night. I first observed it at 9.15, when the 

 streamers appeared somewhat less bright than the Milky Way. 

 Ten minutes later one streamer, about 15° west of north, 

 brightened considerably, and appeared of a pale reddish-yellow 

 tint. It fluctuated in intensity, and soon became less bright. 

 The streamers, which inclined slightly to the west of the vertical, 

 extended to about 30° to 40° above the horizon. 



I watched them till 9.50, when they seemed fading in intensity, 

 and when I looked again at 10.30 they had disappeared entirely. 



Arthur E. Brown. 



Thought Cot, Brentwood, April 26. 



Pigments of Lepidoptera. 

 The appearance of Mr. F. Gowland Hopkins's letter on this 

 subject in the last issue of Nature (p. 581) demands a brief 

 explanation from me — although it is not easy to reply satis- 

 factorily within narrow limits — and the more so since Mr. 

 Hopkins appears to have somewhat misunderstood my stand- 

 point. 



NO. II 74, VOL. 45] 



Let me first acknowledge the courteous tone of Mr. Hopkins's 

 letter, and express my sense of the value to myself of 

 criticism from his pen, and the more so since I have been 

 labouring under the disadvantage of being practically entirely 

 uncriticized so far — a disadvantage that 1 have not failed to 

 appreciate. 



Now, Mr. Hopkins remarks : "Mr. Coste's experiments are 

 very useful as forming a method of classifying these pigments ; 

 but . . . they are of far too empirical a nature for any con- 

 siderations as to the constitution of the bodies to be based upon 

 them." 



Here it is that Mr. Hopkins appears to have missed the point 

 of my work. If he will do me the favour to refer to the 

 detailed account of my experiments in the Entomologist, passim, I 

 think that he will find it tolerably clearly emphasized that my 

 interest in this work, so far, has been almost entirely biological. 

 I stated expressly in my opening article that my object had 

 been to discover, if possible, the genealogies of the colours, and 

 to obtain evidence (so far as coloric characters could afford it) 

 of the phylogenetic relations of allied species : and I may perhaps 

 add that the results obtained have enabled me to predict several 

 varieties of whose occurrence in the natural state I have since 

 been informed. So that Mr. Hopkins is mildly reproaching 

 me because my work does not tend in a direction at which it was 

 not originally aimed, while he is at the same time good enough 

 to admit that it is of some use for the end at which it was aimed. 



However, it was only to be anticipated that one could not go 

 very far without becoming involved in the further question as 

 to the constitution of the pigments ; but here I was met by 

 three considerations. In the first place, I was anxious to obtain 

 first of all as much as possible of what Mr. Hopkins designates 

 "empirical" evidence as to the reactions and classification of 

 the pigments before making any researches at all into their con- 

 stitution ; secondly, the amount of material at my command was 

 far too scanty for any even approximate analysis ; and in the 

 third place, shortly after my experiments had been commenced, 

 my attention was drawn to an abstract of a paper by Mr. 

 Hopkins on the constitution of the yellow pigments. Finding 

 that he was already in possession of the field here, I felt almost 

 bound to leave this part of the subject alone, at least for the 

 present ; and I think that I may say that I have on the whole 

 taken exaggerated care not to extend my experiments into that 

 quarter where Mr. Hopkins was engaged, or to avail myself of 

 the discoveries that he had already made, in order to trespass 

 on his investigations. Putting aside my provisional suggestions 

 as to the nature of the "reversion effect," it has only been at a 

 comparatively recent stage of my work, and in consequence of 

 experiments that have not yet been published, that I have at all 

 turned my attention to the constitution of the pigments ; 

 these results being such as would have compelled me to consider 

 the question even had I heard nothing of Mr. Hopkins's work. 

 I hope that this explanation will put me right in Mr. Hopkins's 

 eyes, and will satisfy him that he has considerably misunder- 

 stood the spirit of "some remarks [perhaps clumsily expressed 

 by me] made at the close of the last article " ; and that it will 

 also satisfy him as to the question of priority. I had no thought 

 of questioning Mr. Hopkins's priority in his own work, and the 

 less so since I have throughout been under the impression that 

 we were working mainly on different — though sometimes 

 adjacent — lines. 



I must not so far trespass upon your space as to criticize Mr. 

 Hopkins's criticisms upon the " reversion effect " ; but I will 

 ask him kindly to examine the detailed accounts of the 

 " reversion " experiments which I gave in the Entomologist, 

 since his remarks appear to me somewhat to ignore the evidence 

 there brought forward : and at the same time I may remark that 

 his statements as to the constitution of the yellow pigments 

 appear to me hardly to invalidate, but rather indirectly to confirm, 

 the suggestions made by nie as to the reversion reaction with red 

 pigments. The new information that Mr. Hopkins promises in 

 his closing paragraph I shall look forward to with great interest. 



April 22. F. H. Perry Coste. 



I was about to pen some remarks on Mr. Perry Coste's recent 

 articles on this subject, when a letter from Mr. Gowland 

 Hopkins in the last number of Nature (p. 581) expressed 

 substantially the same views as those which I had arrived at. 

 I write now rather to support Mr. Hopkins in his strictures 

 than to offer any fresh criticisms of my own. The articles on 

 "Insect Colours" published in these columns are, as the author 



