SECT. ii. BY 1HE PERFUMES OF PLANTS. 4} 



The absorption of thyme and lavender shows how 

 much aroma is lost when plants are dried. So great 

 is the absorption of heat, that the perfume of a flower- 

 bed may be more efficacious than the entire oxygen and 

 nitrogen of the atmosphere above it. 



The enormous absorption and consequently radiating 

 power of the perfumes of plants and flowers is a proof 

 that their constituent parts are molecules and not 

 simple atoms, incredible as it may seem. The absolute 

 weight of the substances producing these wonderful 

 effects is unknown, but there must be great differences : 

 some perfumes are carried to vast distances, others are 

 less volatile, and that of mignonette was remarked by 

 Dr. Wollaston to be absolutely so heavy that it was 

 quite as powerful below a balcony containing a box of 

 that plant, as in the balcony itself. 



The perfumes during the experiments adhered to all 

 parts of the apparatus so pertinaciously, that after a con- 

 tinued stream of dry air had been pumped through the 

 tube till the exhaustion seemed to be complete and the 

 needle stood at zero, after a few minutes' repose, the 

 residue of the perfume came out so powerfully from the 

 crannies of the apparatus as almost to restore the 

 original deflection. ' The quantities of those residues 

 must be left to the imagination to conceive. If they 

 were multiplied by billions they probably would not 

 obtain the density of the air.' 



The absorptive power of the odour of musk was 72 or 

 74 times that of the air that conveyed it into the ex- 

 perimental tube; the quantity that produced it was 

 quite inappreciable, yet the perfume was so persistent 

 that the pieces of the apparatus through which it had 

 passed had to be boiled in a solution of soda before they 

 were fit for other experiments. 



The absorption of many gases and vapours having 

 been determined, their radiation was measured by a 





