88 Dr Stark on the Irtflumce of Colour on Odours. 



tinctly felt. * Diodorus Siculus says something analogous of 

 the coast of Arabia ; and Bartholin states, that the odour of 

 rosemary was recognised forty miles from the coast of Spain. -j- 



Certain odours, or odoriferous particles, it is well known, 

 combine with, or adhere in preference to, different bodies, and 

 the presence or absence of heat, light, moisture, &c. are known to 

 modify their action. Some odours are found to be more easily 

 retained by spirituous fluids ; other are attached by oils ; alcohol 

 is the best vehicle for balsamic substances ; and fat bodies absorb 

 best the odour of the LUiacece. Gloves and paper, as men- 

 tioned before, preserve for a long time the odour of ambergris ; 

 paper and cotton that of musk ; while wool is said to retain fetid 

 odours strongly. It is upon the knowledge of these facts that 

 the fabrication of essences, pommades, pastilles, &c. is founded ; 

 and it is by this means that the fragrance of spring and summer 

 is perpetuated through the winter months. 



There is one quality in odours which requires to be particu- 

 larly mentioned, and that is, their capability of being acted upon 

 by moisture and heat. By whatever means this is accomplished, 

 whether by setting free or dissolving the latent odorous par- 

 ticles, or by merely increasing their intensity of action, the fact 

 is certain, and matter of ordinary observation. Every one must 

 have perceived the increased intensity of odorous emanations 

 in a garden or field after a summer's shower ; and the almost 

 insupportable fetid exhalations which arise from stagnant water 

 in ditches in the same circumstances, is equally well known. 

 The emanations from ditches, indeed, show the existence of mois- 

 ture in the atmosphere before rain, and afford the husbandman 

 an indication of the coming shower. 



It is not my object here to enter into details concerning the 

 nature of the different odours, their classification, or particular 

 effects. Linnaeus has classed vegetable odours in seven sections^ ; 

 Fourcroy has divided them into five genera § ; Haller attempted 

 to class them in two divisions, as they were agreeable or the re- 

 verse; and others have classed odours, as they were produced 



• Lord "Valentia*8 Travels. t Osphresiologie, p. 51. 



X Amen. Acad. torn. iii. p. 195. 



§ Annales de Cliimie, torn. xxvi. p. 232, 



