March 26, 1903] 



NA TURE 



487 



pressed for taste and smell by Haycraft (Proc. Roy. Soc. 

 Edin., 1883-1887). 



But we now know gaseous bodies ranging over the whole 

 domain of molecular weights appropriated by odorous and 

 sapid substances, owing to Ramsay's well-known work on 

 He, \e, A, Kr and X, and to the discovery of SO,F„ and 

 SFJ by Moissan (Compies rendus, cxxx. 1900, 865 and cxxxii. 

 1901, 374). These last two gases are of special importance 

 because their want of taste and odour cannot be due to the 

 fact that we have become inured to them. The molecular 

 weights of these bodies are respectively 4, 20, 40, 81, 127, 

 102 and 146, with which may be compared vanillin, with a 

 molecular weight of 152. 



It was long ago pointed out by Liebig (see Klimont, " Die 

 Synthetischen und Isolirten Aromatica," 1899) and by 

 Graham (see Bain, loc. cit.) that odorous bodies are, as a 

 rule, readily oxidised, and the notion of the chemical origin 

 of the senses in question is much strengthened by the 

 fact that all the new gases above mentioned are very inert. 

 sol'., although soluble in ten parts of water, can only be 

 decomposed by oxygen by sparking, and SF C is extra- 

 ordinarily stable. It is recorded also by Graham that if an 

 odoriferous principle is sniffed up in a current of CO. instead 

 of air, the odour is much weakened. 



There is another curious fact whii h might be accounted 

 for bv a chemical hypothesis. It has often been noticed 

 that on purifying odorous or sapid substances, these pro- 

 perties tend to become less marked or to disappear. Thus 

 acetylene, ammonia and acetamide have been described as 

 odourless when pure, and it is said that ordinary sugar 

 becomes less sweet the more it is purified. But it has been 

 found in all carefully studied cases that stability increases 

 very markedly with purity, and therefore on a chemical 

 theory taste and smell would become correspondingly less. 



In conclusion must be noted Prof. Ayrton's important 

 contribution to this subject (Presid. Address to Section A. 

 British Association, 1898), in which he definitely proyes that 

 the well-known metallic odours are not caused by the metals 

 themselves (which are non-volatile), but by unstable de- 

 composition products, probably unsaturated hydrocarbons. 



Such a chemical explanation would not, of course, upset 

 the vibration theory of Ramsay, but would merely mean 

 that instead of these senses being directly stimulated by the 

 ordinary vibrations of the molecules, they are only affected 

 by agitations accompanying chemical change. 



F. SOUTHERDEN. 



Technical College, Finsbury, London, E.C., March 21. 



Electricity and Matter. 



In view of the suggestive close of Sir Oliver Lodge's 

 paper as given in Nature of March 12, these more than 

 century-old speculations of S. T. Coleridge may be found 

 interesting. E. H. 



■ But properties are God : the naked mass 

 (If mass there be, fantastic guess or ghost) 

 Acts only by its inactivity. 



Here we pause humbly. Others boldlier think 

 that as one bn>dy seems the aggregate 

 Of atoms numberless, each organized ; 

 So by a strange and dim similitude 

 Infinite myriads of self-conscious minds 

 Are one all-conscious Spirit, which informs 

 With absolute ubiquity of thought 

 (His one eternal self-affirming act ! ) 

 All his involved Monads, that yet seem 

 With various province and apt agency 

 Each to pursue its own self-centring end.' 



(From " The Destiny of Nations — A Vision," Juvenile 

 Poems, S. T. Coleridge.) 



Papaw-Trees and Mosquitoes. 



Re Prof. Percy Groom's letter in Nature (January 22, p. 

 271), I may mention that in Ceylon the papaw-tree gives 

 no immunity against mosquitoes. In my garden here we 

 usually take our afternoon tea under the shade of an old 

 and much-branched example of the common papaw (Carica 

 papaia), but far from being protected from mosquito bites 

 in that situation, we are always terribly molested by the 

 small striped mosquito (Stegomyia scutellaris). The stem 

 of this tree is also haunted by various spiders and flies. I 



NO. 1743, VOL - 67] 



have not sufficiently studied the tree during the sunny part 

 of the day to say whether flies settle on the leaves or not, 

 but I propose to pay attention to this question shortly. 



E. Ernest Green. 

 Royal Botanic Gardens, Peradeniya, Ceylon, February 26. 



A Remarkable Meteor. 



With reference to the meteor a letter of mine concerning 

 which you printed in your last issue (p. 464), I have received 

 some details from Mr. G. S. Russell, of West Norwood, 

 who saw it from the neighbourhood of the Crystal Palace. 

 From the facts that he saw it E.N.E. (as I did) and saw 

 the " wobbling " close to earth, it is seen that the meteor 

 must have been a great distance off, probably falling a 

 considerable distance out in the North Sea. He is convinced 

 that it reached the earth's surface. Its great distance off 

 would account for its apparently very slow movement. 

 Owing to the steadiness of both its brilliancy and velocity 

 it was probably of great size. J. E. C. Liddle. 



Fairfields, Basingstoke, Hants, March 23. 



THE MOVEMENT OF AIR STUDIED BY 

 CHRONOPHOTOGRAPHY. 



THE investigation of stream lines has occupied the 

 minds of several powerful workers, and great 

 results have been obtained by the late W. Froude and 

 Prof. O. Reynolds, and recently Prof. Hele Shaw has 

 added some striking illustrations of the paths of the 

 flow of liquids. Borda, in an almost forgotten, but 

 remarkable paper (Mcmoires de V 'Academic Royal, 

 1766), writes thus (when describing the conditions 

 under which water flows by an opposing object) : — 

 " On imagine ensuit que les molecules du fluid, en 

 s'approchant du corps, decrivent des lignes courbes, 

 ou plutot se meuvent dans les petit s banaux courbes." 

 Borda goes on to show that theoretically the stream 

 lines should flow round and again join in the rear of 

 the object. 



Thus the idea of stream lines and their behaviour 

 was regarded as a matter of interest at an early date. 



In a recent paper, in the Bulletin des Seances de la 

 Societe Francois de Physique, 1902, M. Marey has 

 added fresh information respecting the form of stream- 

 lines, and by his new experimental methods he shows 

 how air behaves as it flows by different shaped objects. 

 In the first place he draws attention to his experiments 

 on the movements of liquids in which he employed a 

 stream of water, holding in suspension shining pearls 

 of the same density as water ; these were brightly illu- 

 minated by sunlight, a dark background being placed 

 behind them ; by means of a chronophotographic ap- 

 paratus, a series of pictures of the illuminated parts was 

 taken, their appearance in the picture being that of 

 dotted lines. The direction and speed of the current 

 which carried them along was by this means found. 



When obstacles of different shapes were placed in 

 the current the stream lines of the liquid were seen 

 to bend in different ways and to form eddies. For ex- 

 ample, in the case of water impinging against an in- 

 clined plane, the streams of liquid divide at a point, 

 which appears to be the centre of pressure. In each 

 case eddies form in the rear of the obstacle. The 

 speed of the fluid, at any moment, could be recognised 

 on the photograms by the degree of separation of the 

 shining pearls, for photographed as they were, at 

 equal times, they covered different distances in 

 these equal intervals of time. A divided scale gave' 

 the lengths of these distances covered, while the rate 

 of taking the successive pictures (ten per second) gave 

 the speed of the current in its various positions. 



Bv means of a method similar to this the direction 

 and speed of the streams which form in a current of 



