ODOURS. 163 



square of the distance from the substance that exhales them. There 

 is a great difference, however, in odours as- regards their diffusibility in 

 the atmosphere. Some extend to a great distance, whilst others are 

 confined within a small compass. The odours of many flowers are so 

 delicate as not to be appreciated, unless they are brought near the 

 olfactory organs ; whilst that of cinnamon is said to have been detected 

 at sea, at the distance of twenty-five miles from Ceylon. Lord Valen- 

 tia 1 affirms, that he himself distinctly smelt the aromatic gale at nine 

 leagues' distance ; but Dr. Ruschenberger 2 was not equally fortunate. 

 The author was informed by Commodore Stewart, of the Navy, that 

 he had discovered the spicy emanations when two hundred miles from 

 Ceylon; and the terebinthinate odours of the pines of Virginia, when 

 one hundred miles from the coast; and the author's friend, Dr. Wil- 

 cocks, of Philadelphia, when at sea in 1844, and two hundred miles to 

 the westward of the coast of Ireland, observed, as did many others of 

 the passengers, a smoky odour, which lasted for several days in suc- 

 cession. On appealing to the captain for the cause of the phenomenon, 

 he informed them that he had frequently remarked it before ; and 

 that it was owing to the long continuance of easterly winds, which 

 carried the odour of burning peat from Ireland far out to sea. 3 Facts 

 of this kind are employed by the natural philosopher to exhibit the 

 excessive divisibility of matter. Scales, in which a few grains of 

 musk have been weighed, have retained the smell for twenty years 

 afterwards, although they must have been constantly exhaling odorous 

 molecules during the whole of this period. Haller 4 kept some papers, 

 for more than forty years, which had been perfumed by a single grain 

 of amber; and, at the end of that time, they did not appear to have 

 lost any of their odour. ITiat distinguished physiologist and mathe- 

 matician calculated, that every inch of their surface had been im- 

 pregnated by SATO'S 4^0^ f a g ra i n of amber, and yet they had 

 scented for 14,600 days a stratum of air at least a foot in thickness. 

 But how much larger must these molecules be than those of light 

 provided we regard it as consisting of molecules seeing that glass is 

 capable of arresting the former, but suffers the other to penetrate it in 

 every direction. 



Nor need we be so much surprised at the excessive diffusibility of 

 odorous particles, when we call to mind the facts on record in regard 

 to the transmission through the air of fine particles of sand. Gene- 

 rally, according to Mr. Darwin, 5 the atmosphere of the Cape Yerd 

 Islands is hazy ; and this is caused by the falling of impalpably fine 

 dust, which was found to have slightly injured the astronomical instru- 

 ments. The morning before they anchored at Porto Praya, he collected 

 a little packet of this brown-coloured fine dust, which appeared to have 



1 Voyages and Travels in India. London, 1809. 



3 Embassy to the courts of Muscat and Siam, &c., p. 154. Philad., 1838. 



3 Medical Examiner, March, 1846, p. 159. 



4 Elementa Physiolog., torn. v. lib. xiv. sect. 2, p. 157. Lausann., 1769. 



5 Journal of Researches into the Natural History and Geology of the countries visited 

 during the voyage of H. M. S. Beagle round the world, &c. Amer. edit., i. 5. New York, 

 1846. 



