304 



NATURE 



[June 19, 1919 



cists, but also by those engaged in other scientific 

 pursuits who desire trustworthy information as 

 to the "new physics." H. S. A. 



Le Rocce. Concetti e Nozioni di Petrografia. 



By Prof. E. Artini. Pp. xx + 636 + Tav. xxxii. 



(Milano : Ulrico Hoepli, 1919.) Price 18.50 lire. 

 Prof. Artini states in his preface that there has 

 been no general treatise on rocks in the Italian 

 language since that by Achiardi, published thirty 

 years ago. He rightly remarks that a transla- 

 tion is always an indifferent expedient ; a book for 

 Italians should be rich in ItaUan examples. He 

 looks on rocks from the point of view of a 

 naturalist, and his use of landscapes among his 

 illustrations makes us hope that he will some day 

 give us a petrography of Italy that will connect 

 mineral evolution with the scenery from Monte 

 Bianco to Catania. The material here brought 

 together is thoroughly up to date ; we may cite, for 

 instance, the remarks on idrogels (p. 186), on 

 bipyramidal quartz (p. 338), and on the alleged 

 gneissic Grundgebirge (p. 544). Graphic methods 

 of representing rock-composition are illustrated. 

 As an Italian detail, may we point out (p. 319) 

 that gabhro, and not eufotide, is of Tuscan origin, 

 the name of a Tuscan village having been utilised 

 by von Buch? The treatment of sedimentary 

 rocks is unusually adequate, and the photographic 

 plates of thin sections are extremely clear and 

 helpful. This compact volume is so full of funda- 

 mental concetti that it certainly should have been 

 provided with an index. G. A. J. C. 



Agricultural Bacteriology. By Dr. H. W. Conn. 

 Third edition, revised by H. J. Conn. Pp. x + 

 357. (Philadelphia : P. Blakiston's Son and 

 Co., 1918.) Price 2 dollars net. 

 While the general plan of this book remains the 

 same as before, considerable changes have been 

 introduced in the sections on soil bacteriology, 

 on the control of milk supplies, on plant diseases, 

 and on laboratory technique. In some cases, 

 however, further information might have been 

 given with advantage ; thus under slimy or ropy 

 bread practically no description is given of the 

 causative organism. Under " tuberculosis " the il- 

 lustration Fig. 50 is stated to depict " a bit of ani- 

 mal tissue " ; what is actually shown is a giant cell 

 only ; the tubercles are stated to be " swollen 

 masses of tissue," and among animals that suffer 

 from tuberculosis dogs and cats are mentioned ; 

 actually these animals rarely suffer from the 

 disease. The consideration of the bacteriology of 

 the soil, of milk, and of milk products is adequate, 

 and such details as protozoa in the soil and soil 

 sterilisation and the possibility of the accumula- 

 tion of toxic substances in "worn-out soils " are 

 all referred to. In an appendix a scheme of 

 laboratory work is given, with detailed exercises, 

 which should be of value to the teacher. The 

 book is freely illustrated and clearly printed, and 

 forms a good elementary introduction to the wide 

 subject of agricultural bacteriology. 



R. T. H. 

 NO. 2590, VOL. 103] 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for 

 opinions expressed 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 Nature. No notice is 

 taken of anonymous communications.] 



Wireless Telephony. 



Referring to my letter on this subject in Nature 

 of June 12, Mr. Godfrey Isaacs tells me that his 

 wireless remarks with regard to secrecy were intended 

 to apply, not to the apparatus actually in use on 

 May 28, but to a new Marconi system, the apparatus 

 for which is only now In course of manufacture. The 

 scientific world will, I am sure, await with interest 

 details of this new secret wireless telephone system. 

 A. A. Campbell Swinton. 



40 Chester Square, London, S.W. i, June 17. 



Camouflage of Ships of War. | 



Prof. Kerr, in the course of a letter which aplj 

 peared in Nature of May 15 under the above heading, 

 paid me a high tribute by stating that, during the 

 summer of 1917, "the value of the principle [i.e. 

 obliterative colouring] was now recognised [by the 

 Admiralty] and its application entrusted to skilled 

 hands," but the main point in his letter was to show 

 that the principle of obliterative colourine^ was no 

 new thing, and was common knowledge to biologists : 

 this no one will question. My aim in replying to his 

 letter is with the view of showing that I was not 

 working on biological lines, and is thus to remove a 

 misapprehension . 



I feel that Prof. Kerr has not thoroughly grasped 

 the idea of the special form of camouflage on which 

 I was engaged, and of which I still claim to be the 

 originator. "Dazzle-painting," so called officially, 

 had one purpose in view only, viz. to upset a sub- 

 marine commander's estimate of a vessel's course, 

 when carrying out an attack with torpedo. I was 

 under no misapprehension as to its value for gunnery, 

 and in my original submission to the Admiralty in 

 May, 19 17, I made no claim that it might be used for 

 this purpose, as I felt certain that paint could not 

 possibly have sufficient carrying power to stultify the 

 enemy's range-finders at the great distances at which 

 a modern action would probably be fought. 



Subsequent experiments on dazzled ships with 

 range-finders justified this belief. 



The accurate estimation of a vessel's course is the 

 prime factor required by a submarine commander to 

 ensure successful attack. In every dazzle design this 

 point was studied to the exclusion of all others, i.e. 

 to frustrate accurate calculation of course. The mere 

 breaking up of a vessel's form bv strong-ly contrast- 

 ing colours would not achieve this end without careful 

 studv of the perspective and balance of the design. 

 I arn not aware that this occurs in biology, i.e. the 

 disfifulse of direction. 



Surelv the obliterative colouring- of birds and animals 

 is operative only so long as the bird or animal is in 

 a state of rest; the moment movement commences 

 the Illusion is destroyed. The ship subject to torpedo 

 attack is in constant movement. Again, in how 

 many cases is Nature's scheme for protection success- 

 ful when the subject is seen on a ridge silhouetted 

 against the sky? Yet this is the only point of view 

 from a submarine when observing a ship through the 

 periscope. 





