OJV THE DIFFUSION OF ODORS. 85 



More than thirty-six years ago I announced, in some lectures I was 

 then engaged in delivering, that there were some facts in the phenom- 

 ena of odors and the sense of smell that were incompatible with the 

 effluvia or diifusion-of -particles theory ; and I suggested an explana- 

 tion based on the idea of a vibration or wave-motion, and an " odorif- 

 erous ether " analogous to, if not identical with, that of the luminif er- 



ous ether. 



In the year 1863, in a letter to Professor Tyndall, I submitted the 

 thought to him. After quoting some passages from his book, " Heat 

 a Mode of Motion," upon the subject of odors, I wrote as follows : " I 

 would respectfully ask if, in the consideration of, or in the course of, 

 experiments upon this subject, it has ever occurred to you that odor 

 might be as essentially a " mode of motion " as heat, light, or sound ? 

 . . . The seemingly unlimited generation of odoriferous particles (?) 

 by certain substances, without sensible diminution of bulk or weight, 

 first led to the conception that, however copiously odoriferous particles 

 of matter were disseminated through the atmosphere, the odorous prop- 

 erty itself was as purely a specific variety of motion as the undulations 

 of the luminif erous ether. That this must be the explanation of the 

 action of the odor-generating force for a part of its route to the hu- 

 man sensorium seems to be incontrovertible, for it is hardly conceiv- 

 able that the material particles should actually penetrate the membrane 

 and force their way, as moving bodies, through the pulpy tissue of 

 the nerves to the seat of sensation ; but that through that portion of 

 their career, at least, their power is propagated by wave-like motions 

 analogous to those of heat and sound." 



Professor Tyndall did me the honor to answer my letter, but not to 

 indorse my view, except in a very faint and qualified manner. Never- 

 theless, reflection and added experience have only gone to confirm me 

 in the correctness of it, and I venture to predict that before many 

 years it will be as much an accepted fact of science as the undulatory, 

 luminiferous-ether theory now is. 



In the case given above the entire space of the chamber is thor- 

 oughly impregnated with the perfume as much as if it were an abso- 

 lute solid of odor. And yet these "particles," so profusely diffused 

 through the room, are wafted away, and their places supplied by new 

 emissions from the undiminished " grain," " many thousands of times ' : 

 every year without appreciable " sensible diminution of its volume or 

 weight," or pungency. This is an obvious impossibility upon any the- 

 ory of molecular Or atomic diffusion. The assumption of immense dif- 

 fusibility and vastness of inter-particular spaces would only enhance 

 the difficulty, for the odor spans the spaces is as absolutely continu- 

 ous as if the particles were in actual contact. That is, in the given 

 space, the chamber, anywhere within the limits of the odor, there is 

 no place where it is not. This actio in distans implies ethereal motion 

 vibration between the particles. 



