May 29, 1913] 



NATURE 



319 



of quinine ; morphine and the opium alkaloids, 

 and strychnine and brucine, occupy the next places 

 of importance, whilst the remaining- alkaloids are 

 very briefly discussed. It is essentially a com- 

 pilation, and, like all compilations, has a distinct 

 value. In this case the value is somewhat ad- 

 versely affected by the scanty treatment that some 

 of the alkaloids have received. Thus the separa- 

 tion of emetine from cephaeline is simply men- 

 tioned, although Paul and Cownley showed long 

 atro how it could be effected, and Farr and 

 Wright have published a method for the accurate 

 determination of colchicine, to which no reference 

 is made; indeed, the results obtained by English 

 workers in this field have been sadly neglected. 

 The utility of the work would be much enhanced 

 by a more thorough examination of the literature. 



Manual of IVireless Telegraphy and Telephony. 

 By A. F. Collins. Third edition. Pp. xv+300. 

 ( New York : John Wiley and Sons ; London : 

 Chapman and Hall, 1913.) Price 65. 6d. net. 

 ' This edition differs from the first, which was 

 reviewed in the issue of Nature for February 14, 

 1907 (vol. lxxv., p. 366), in several respects. The 

 improvements in apparatus, and the advances 

 made in wireless telegraphy in other directions, 

 have led Mr. Collins to extend his treatment of 

 the apparatus of a commercial station, and to 

 describe the transmitting and the receiving instru- 

 ments in separate chapters. The suggestions to 

 operators relating' to the management of stations 

 are more exhaustive, and other useful additions 

 have been made. 



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 cotnmunications.] 



Artificial Hiss. 



Can any of your readers tell me how to make an 

 artificial hiss? I have heard something like one from 

 steam blowing off at a safety-valve. There the pres- 

 sure was very high, but in the mouth a hiss is made 

 with a moderate pressure behind. The problem must 

 have been faced by inventors of speaking machines, 

 but I do not know with what success. The best that 

 I have been able to do myself is by blowing through 

 a rubber tube nipped at about half an inch from the 

 end with a screw clamp, but the sound is perhaps 

 more like an / than an s. 



There is reason to think that the ear, at any rate 

 of elderly people, tires rapidly to a maintained hiss. 

 The pitch is of the order of 10,000 per second. 



Ravleigh. 



Terling Place, Witham, Essex. 



persons occupied in work often apparently of a very 

 unmathematical nature. 



.Mr. Cripps (May 15, p. 270) appears to belong to the 

 unfortunately too prevalent class of individual who 

 mistakes algebra for mathematics, and he bases his 

 objection entirely on the purely algebraic equation 

 l = M + i. He completely overlooks the fact that Mr. 

 Potts's method is based entirely on the great and 

 powerful conception of functionality. But if I under- 

 stand Mr. Potts correctly, the problem in which he is 

 an expert consists in determining the forms and char- 

 acteristics of certain functions, and not in the mere 

 numerical solution of equations. G. H. Bryan'. 



An Application of Mathematics to Law. 



I would not have troubled you with further corre- 

 spondence on this subject but for the fact that Mr. 

 Potts's letter (April 24, p. 1S7) illustrates in a re- 

 markable way the value of a knowledge of the funda- 

 mental principles of mathematics when possessed by 



NO. 2274, VOL. 91] 



Overheated Water. 



Tin-: experiment of Dufour, in which drops of water 

 were suspended in a mixture of linseed oil and oil 

 of cloves, and heated to 120 C. without boiling, is 

 seldom repeated for class demonstration, presumably 

 owing to the difficulty of preparing a mixture of the 

 oils exactly equal in density to water at the tempera- 

 ture named. The phenomenon may be shown with 

 ease and certainty, however, by employing a mixture 

 of four volumes of ethyl benzoate and one volume of 

 aniline instead of the mixture of oils, the procedure 

 being as follows : — Place 80 c.c. of ethyl benzoate and 

 20 c.c. of aniline in a beaker, and surround by a 

 bath of glycerine or strong sulphuric acid. Heat the 

 bath until the temperature of the mixture is 125 C, 

 and then add 2 to 5 c.c. of freshly boiled water by 

 means of a pipette. The water will sink at first, 

 and rest on the bottom of the beaker; but on attaining 

 the temperature of the mixed liquids it will break up 

 with some violence into spheres of various sizes, which 

 remain floating in the liquid so long as the equi-density 

 temperature of 125 C. is maintained. It is advisable 

 to place a cover over the beaker to prevent the fuming 

 of the mixture. 



For lantern projection, a copper vessel, square in 

 section, and having two opposite sides of patent plate- 

 glass, will be found satisfactory, glycerine being used 

 to surround the beaker and the temperature raised 

 gradually. Chas. R. Darling. 



City and Guilds Technical College, Finsbury, E.C. 



"Coal, and the Prevention of Explosions and Fires 

 in Mines." 



I must point out that some of the statements in 

 your review of the above book in Nature of April 24 

 are inaccurate. 



"Great explosions do not, as Dr. Harger imagines, 

 travel either exclusively or generally against the 

 direction of the ventilating currents." What I say 

 in the book (p. 78) which your reviewer is presumably 

 criticising is this: — "All big dust explosions are 

 similar to the one at Altofts. Ignition is followed by 

 quiet combustion for 50-100 yards, then the wave of 

 progressive combustion gathers speed, and finally 

 attains a velocity approaching that of detonation, and 

 races through the dust and air at a speed of 50-100 

 miles per minute. Such dust explosions always pro- 

 ceed against the current of air ; sometimes they go 

 the other way also, but seldom reach the working; 

 faces. • As a rule the branch of an ignition which 

 travels with the air current fails to develop violence," 

 &c. 



Every dust explosion in a mine on record has 

 travelled against the air current, and the reason for 

 this is clearly put in my paper on gob fires and the 

 prevention of gob fires in mines, which your reviewer 

 quotes, and also on pp. q8-ioo in the book. 



Your reviewer quotes Proc. Roy. Soc, vol. xxviii., 



