MINUTENESS OF ODORIFEROUS PARTICLES. 205 



material particles, volatilized in the atmosphere. But here 

 matter seems to become intangible. The chemist can ex- 

 tract from a body the essential oil which gives it its odour, 

 but he cannot separate the odoriferous principle from the oil 

 itself, and he can only recognize its presence by the special 

 impression received by the olfactory nerve. 



Nothing gives us a more exact idea of the divisibility of 

 matter than the diffusion of odours. Three-quarters of a grain 

 of musk placed in a room cause a very powerful smell for a 

 considerable length of time without any sensible diminution 

 in weight, and the box in which musk has been placed 

 retains the perfume for an almost indefinite period. Haller 

 relates that some papers which had been perfumed by a 

 grain of ambergris, were still very odoriferous after a lapse 

 of forty years. 



Odours are transported by the air to a considerable dis- 

 tance. A dog recognizes his master's approach by smell 

 even when he is far away; and we are assured by navigators 

 that the winds bring the delicious odours of the balmy forests 

 of Ceylon to a distance of ten leagues from the coast. 



Simple experiments prove that odoriferous bodies emit a 

 stream of particles so small as to seem to be immaterial. 

 When a morsel of camphor or a small body saturated with 

 ether, or minute portions of benzoic acid, are thrown upon 

 water, they are animated by a peculiar movement, which is 

 due to the propulsion produced by the invisible vapour 

 which emanates from these substances. 



Heat, light, and other influences modify the production of 

 odours, and their transmission in space. Certain plants are 

 odoriferous only at night, and it is especially in the morning 

 and evening, when the dew is scanty, that flower-gardens 

 perfume the atmosphere. Rain destroys the perfume of 

 flowers, probably by its mechanical action, and by lowering 

 their temperature. It is remarkable also that animal or 

 vegetable odours are feebler, as the countries are colder in 

 which the plants or animals live from which they emanate. 

 Hence perfumes come principally from tropical countries. 



It has been stated that substances absorb and retain odours 

 according to their colour, Thus, the experiments of Stark 



