January i8, 19 12] 



NATURE 



Ml 



The American Annual of Photography, 1912. Vol. 

 xxvi. Edited by Percy Y. Howe. Pp. 328. (New- 

 York : The American Annual of Photography ; 

 London : G. Routledge and Sons, Ltd., 1911.) Price 

 35. 6d. 

 In these pages the photographic reader will find much 

 that will interest him, for a host of photographic 

 subjects are delightfully treated, and the illustrations 

 are both numerous and good. Turning over the pages 

 one finds some simple hints regarding telephoto 

 lenses, then a brief discourse on the fascinating pro- 

 cedure of taking photographs against the light pro- 

 ductive of many pretty pictures. Simple apparatus 

 for photomicrography and sensitising platinum paper 

 are later dealt with, followed by an interesting article 

 on "Daguerreotype Copying." 'Much useful informa- 

 tion is imparted to the reader in the articles on stereo- 

 scopic night scenes, botanical photography, colouring 

 photographs, the English cathedrals, &c. Nearly all 

 the various subjects dealt with are well illustrated, 

 and these add greatly to the value of the annual. At 

 the end there is brought together a typical collection 

 of formulae and tables which will no doubt be found 

 useful to the working photographer. Good indices to 

 the articles, subjects, illustrators, and advertisers 

 facilitate easy references to the various portions of 

 the book. 



Einfiihrung in die Mykologie der Nahrungsmittel- 

 gewerbe. By Prof. A. Kossowicz. Pp. viii + 

 138. (Berlin: Gebriider Borntraeger, 191 1.) Price 

 4 marks. 

 This book deals with bacteria, yeasts, and moulds in 

 their special relation to foodstuffs, and forms a wel- 

 come addition to technical bacteriology. Portions of 

 it particularly concern the domestic arts, and would 

 be of service in connection with courses of "domestic 

 or home science," a branch of training which is now 

 coming to the fore. Commencing with a brief intro- 

 duction on the morphology and methods of study of 

 the organisms dealt with, the subjects of milk, butter, 

 rid cheese are first considered. Then follows the 

 ore special section of the book, which is devoted to 

 (he consideration of the decomposition and preserva- 

 tion of meat and fish, eggs, vegetables, and fruit. In 

 this the various organisms producing the "spoiling" 

 of these foodstuffs are briefly considered, together with 

 the chief methods of conserving food. It is interesting 

 to learn that the air of the Cuxhaven fish market is 

 ozonised, with the result that the fishy odour is 

 destroyed. I'inally, the mycology of the bakerv, of 

 sugar, and of fodder is briefiv described. The book 

 i^ a . verv readable one, and is well and sufficiently 

 illustrated. R. T. H. 



LETTERS TO THE EDITOR. 



I Ihr Editor docs tiot hold himself responsible for opinions 

 ixpressed by his correspondents, \either can he undertake 

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

 manuscripts intended for this or any other part of Nature. 

 Vo notice is taken of anonymous communications.] 



Spectroscopic Methods. 



In his interestififj address on spectroscopic methods, 



if. Michelson tails into a not uncommon error when he 



>; that, in order to obtain a pure spectrum, "two 



|)ortant modifications must be made in Newton's arranj^e- 



rit. P'irst, the lij.;ht must be allowed to pass throuj:;li 



v»!ry narrow aperture, and. secondly, a sharp image of 



- aperture must be formed by a lens or mirror." 



l?oth these irodifications were made by Newton himself, 



i with a clear understandinj* of their advantajjes. In 



')pticks,' I^xper. 11, we read: — "In the sun's iif<ht 



into my darkened chamber through a small round hole 



. my window — shut, at about 10 or 12 feet from the 



window. I placed a lens, by whKh the image of the hole 



might bo distinctly cast upon a sheet of white paper, \->Uh<->\ 



NO. 2203, VOL. 88] 



at the distance of six, eight, ten, or twelve feet from the 

 lens. . . . For in this case the circular images of the hole 

 which comprise that image . . . were terminated most 

 distmctly without any penumbra, and therefore extended 

 mto one another the least that thev could, and by con- 

 sequence the mixture of the heterog'eneous ravs wa's now 

 the least of all. " 



And further on : — 



" Yet instead of the circular hole F, 'tis better to sub- 

 stitute an oblong hole shaped like a long parallelogram 

 with its length parallel to the prism ABC. For if this 

 hole be an inch or two long, and but a tenth or twentieth 

 part of an inch broad or narrower, the light of the image 

 pt will be as simple as before or simpler [i.e. as compared 

 with a correspondingly narrow circular hole], and the 

 image will become much broader, and therefore more fit 

 to have experiments tried in its light than before." 



Again, it was not Bunsen and Kirchhoff w-ho first intro- 

 duced the collimator into the spectroscope. Swan 

 employed it in 1847, and fully described its use in Edin. 

 Trans., vol. xvi., p. 375, 1849. See also Edin. Trans., 

 vol. xxi., p. 411, 1857; Pogg. Ann., C, p. 306, 1857. 



These are very minor matters as compared with what 

 Prof. Michelson has to tell of his own achievements and 

 experiences, but it seems desirable that thev should be 

 set right. ' R. 



Are Eyes ever Autophanous ? 



The following communication was written about 1880, 

 soon after my change of residence from Collingwood (in 

 Kent) to Slough (in Buckinghamshire), that is, about 

 twenty-three years ago, and having been laid aside, through 

 the intervention of other interests, has now come to light 

 again in weeding the accumulation of half a rather long 

 lifetime. It seemed unadvisable to recast, from memory, 

 what was set down from present observation. At the same 

 time, the form in which those observations are presented 

 required explanation, such as is now offered. 



I propose in the present letter to describe some observa- 

 tions of a rather unique character, and have thought that 

 the occasion warrants my coining a word in connection 

 with — though not descriptiv'e of — their general nature. I 

 had never given much credence to the sayings and state- 

 ments, not infrequently met with, expressive of a rather 

 widely entertained belief that the eyes of some animals, 

 especially those of the feline genera, have the property of 

 " shining in the dark," of emitting light, or (as I now 

 venture to describe it) of being autophanous. But I saw 

 no prospect of disproving its existence until accident 

 pointed out a ready way of producing the effect, and thus 

 raising a pretty strong presumption as to the true source 

 of the belief. I propose in a few words to put your readers 

 in a position to verify and extend my subsequent experi- 

 ence, and to enable all who try it to judge for themselves 

 whether the suggested explanation is not sufficient, with- 

 out attributing to the eye a specific inherent luminosity. 



.\bout five years ago I was presented with a puppy, of 

 a good breed of collie, the history of which I must briefly 

 summarise by saying that, until I lost him last November, 

 he was my constant companion day and night. His sleep- 

 ing quarters d.uring the spring and summer months of 

 '84 were in a kennel placed on the landing of a flight 

 of stone steps leading up to a garden door facing my 

 habitual seat in an inner room, so that we could always 

 see each other when the intervening doors were open. 

 When there was a lamp on the table it was not long before 

 I learnt to look for, and generally to see, Bruno's great 

 eyes watching me out of the darkness. It is immaterial 

 now to recall exactly by what successive steps I learnt the 

 essential conditions of the phenomenon : they now seem so 

 obvious. Eventually I was led to use a bull's-eye lantern. 

 thf> adoption of which opened the wide field of experience 

 of which I will now endeavour to give some particulars. 

 Let it not be supposed that it is enough to direct the light 

 of a lantern upon a dog's eyes. If such were the case, the 

 observation would long since have been made ; for it is 

 bv no means essential that the dog's sight shall be turned 

 directly upon the source of light, as will presently appear. 

 What is essential, and what makes all the difference 

 between what the holder of the lantern sees and what a 



