470 



NA TURE 



[April 15, 1922 



northern latitudes, and finally discusses periodic 

 alterations of the three elements upon which the dis- 

 tribution of temperature must be based, namely, the 

 temperature of the intertropical belt, the radiative 

 power of the air, and the intensity of the general 

 circulation. He thus outlines a general theory of 

 climatic changes. 



The processes of reasoning are mathematical, and 

 are set out with exemplary clearness ; in order to get 

 numerical results a great number of assumptions are 

 necessarily made. So long as the discussion is con- 

 fined to the consideration of the earth as a whole 

 and normal temperatures are treated as a simple 

 function of the latitude, a good deal of liberty may 

 be allowed in the other assumptions ; but when we 

 get to close quarters with current meteorological 

 experience some of them A\ill naturally need adjust- 

 ment. It seems odd that in dealing with periodic 

 changes the best known periodic change from winter 

 to summer did not challenge the author's curiosity. 

 It seems nearer at hand than the influence of sun- 

 spots or Bruckner's cycle. 



The justification for using the Austausch A as a 

 numerical symbol of the effect of the whole irregular 

 atmospheric motion of middle latitudes would be 

 complete if it could be shown that its measure from 

 time to .time would do instead of the study of the 

 motion itself. From that point of view the winds at 

 Potsdam can be regarded only as a beginning, and 

 not a very good one. The winds at Bergen would 

 certainly tell a very different story. The next step 

 appears to be a closer examination of some data for 

 Austausch. 



One more point is noteworthy. Prof. Defant is 

 apparently under the impression that in consequence 

 of the conservation of momentum winds of 300 m./sec. 

 are a meteorological possibility from the occurrence 

 of which we are saved by the turbulence of middle lati- 

 tudes. What we thought to be the causes of our 

 worst gales appear as our safeguard against being 

 blown away completely by winds of tenfold velocity. 

 But in our practice we have become accustomed to 

 regard winds as inevitably related to pressure differ- 

 ences. Prof. Marvin, of the United States Weather 

 Bureau, has recently pointed out that the idea of 

 winds of 300 m./sec. is one of the common fallacies 

 about the atmosphere that not even the cognoscenti 

 have escaped, and that in face of the " geoidal slope " 

 they could not occur, turbulence or no turbulence. 

 It is, therefore, a httle disconcerting to find that Prof. 

 Defant deploys the power of the Austausch to destroy 

 them : disconcerting for this reason, that we are 

 apparently put in possession of an engine that is power- 

 ful enough to reduce winds of 300 m./sec. to 20 m./sec. 

 NO. 2737, VOL. 109] 



if it were wanted, and it is not wanted. What 

 then becomes of its power ? Has the power of the 

 engine been over-estimated, or has it other work 

 to do ? 



It is true that Prof. Defant's remark is merely an 

 obiter dictum, and has no influence upon his reasoning ; 

 but the same idea stares one in the face from the 

 diagrams of Ferrel, J. Thomson, and others, and is 

 quoted by more recent authors. It is time it was 

 cleared off the field of meteorological theory. 



Napier Shaw. 



Forensic Chemistry. 



Forensic Chemistry. By A. Lucas. Pp. viii -1-268. 

 (London : Edward Arnold and Co., 1921.) 155. net. 



MR. A. LUCAS, who is the director of the Govern- 

 ment Analytical Laboratory and Assay Office, 

 Cairo, claims that his book is the first of its kind in 

 English, with the possible exception of a small work 

 on legal chemistry which he published in 1920, out 

 of which the present work has grown. In a limited 

 sense the claim may be valid, although the distinction 

 between forensic chemistry and forensic medicine, 

 on which latter subject there are many well-established 

 treatises, is one of degree rather than of kind. Hitherto 

 works on forensic medicine have included forensic 

 chemistry. The expert on forensic medicine has 

 usually been a medical man with knowledge and 

 experience of the detection of chemical substances, 

 such as poisons, which may form the subject of criminal 

 investigation. Strictly speaking, the two branches 

 are, however, perfectly distinct, and there has been a 

 growing tendency within recent years to differentiate 

 them. The criminal who contemplates murder, for 

 example, has far more means at his disposal nowadays 

 than formerly. Science has furnished him with 

 methods unknown to former generations, and these 

 can be combated and checked only by methods of 

 science. It was inevitable, therefore, that public 

 security should require the establishment of a special 

 class of expert whose duty should be the study and 

 application of methods of detection and recognition 

 by chemical means of the many agents and appli- 

 ances which may now form the subject of criminal 

 inquiry. 



But forensic or legal chemistry, as Mr. Lucas points 

 out, may be concerned not only with examinations 

 for the presence or absence of particular substances^ 

 such as poisons, but with questions which are only 

 partly chemical, as the examination of blood-stains, 

 questioned documents, counterfeit coins, fibres and 

 textile fabrics — in fact, any problem of criminal 



