TRANSACTIONS OF SECTION A. 775 



tlie motion of the air in diffusing smell was the fact that a strong smell at the free 

 end of the tube could at any time be caused by merely loosening the stopper to 

 which the scented sponge was attached ; lor sniffing at the free end then made 

 a draught through the tube which brought the scent with it. 



Further, all hough the glass tubes were coated outside with a thick layer of 

 non-heat-conducting material, so as to check the formation of convection currents, 

 due to difference in the inside and outside temperature caused by handling, the 

 rate of travel of a smell from a given odoriferous material was found to be much 

 quicker when the tube was vertical than when it was horizontal. But this, I am 

 inclined to think, may have been caused by a small convection current which 

 still was produced in spite of these precautions. 



For, as suggested by Dr. Ramsay several yeai's ago, a substance must have a 

 molecular weight at least fifteen times that of hydrogen to produce a sensation 

 of smell at all, and, further, since camphor, with which many of my experiments 

 have been made, has, when vaporised, a density about five times that of the air, 

 it seems unlikely that scent vapour should ditluse miich more quickly upwards 

 through a vertical column of air than through a horizontal one. At the same 

 time, not only are the tests with the glass tubes very striking, but the general 

 impression which exists that smells rise — indeed the very iact that the nasal 

 channels of animals open downwards — tends to show that, wliether due to draughts 

 or not, smells have really a tendency to ascend. And the following result obtained 

 with glass tubes closed at one end with stoppers carrying respectively camphor, 

 menthol, oil of limes, &c., and at the other end with corks, is instructive on this 

 point. For, on uncorking such a tube after it had been closed for a long time and 

 allowing the odour to stream out of it through the open air towards the experi- 

 menter's face, it was always found that the tube had to be brought much closer 

 when the scent stream was poured downwards than when she was in a vertical 

 position and it was allowed to ascend, although, when it was poured downwards, 

 the experimenter brought her nose into aa favourable a position as possible for 

 receiving the sniell, by lying down with her head thrown well back. 



As an illustration of the inefficiency of diffusion alone to convey a smell 

 you will find that if you hold your bi'eath, without in any way closing your nose 

 either externally or by contracting the nasal muscles, you will experience no 

 smelling sensation even when the no.^e is held close to pepper, or a strong solution 

 of ammonia, or even when camphor in a minute tube is introduced high up into 

 the nostril. Mere diffusion from the lower nasal cavity into the upper cannot 

 apparently take place with sufficient ease to produce the sense of smell, so that an 

 actual stream of air through the upper portion of the nose seems necessary even when 

 the nose is a very sensitive one. This stream, for substances placed outside the 

 nose, is produced by breathing in, no smell being detected while breathing out. 

 On the other hand, if a substance be placed inside the mouth its flavour is recog- 

 nised when the air is forced outwards through the nostrils — that is, at each 

 expiration. Hence we may experience alternately two totally different smells by 

 placing one substance outside the nose and the other in the mouth, the one smell 

 Deing noticed in inhaling and the other in exhaling. And the latter can be 

 increased by smacking the lips, which, I think, has really for its object the forcing 

 of more air through the nostrils at each expiration. 



Experiments on the propagation of smells in a vacuum have also been com- 

 menced in my laboratory, and the results are no less surprising than those obtained 

 with the propagation in air. A U-tube, seven inches high, had the odoriferous 

 substance placed inside it at the top of one limb, and a very good vacuum could be 

 made by allowing mercury to flow out of the tube. Then the two limbs were 

 separated by raising the mercury column, and, air being admitted at the top of 

 the other limb, without its coming into contact with the odoriferous substance, the 

 nose was applied at the top of this limb. 



When liquids like ammoniated lavender smelling-salts, solution of musk, and 

 amyl acetate were employed, and various devices Avere used for introducing the 

 liquid, and preventing its splashing when it boiled on exhausting the air, it was 

 found that the time that it was necessary to leave the two limbs connected for a 



