688 THE POPULAR SCIENCE MONTHLY. 



emission of calorific force. Flowers which by their color emit 

 the most heat, also emit the most perfume. 



The results of the study of the influence of the color of sub- 

 stances on their power of absorbing odors differ a little from 

 these : white, yellow, red, green, and blue absorb odors in a de- 

 creasing order, or rather emit them in an increasing one. These 

 colors represent decreasing luminous powers. 



Ozone develops the energy of essential oils, and perfumes in 

 turn determine by their oxidation in the air the production of 

 ozone. This is a matter of hygienic significance, for the pres- 

 ence of ozone being favorable to health, we have a means at hand 

 of increasing the supply of it by surrounding ourselves with fra- 

 grant substances and flowers. 



Heat favors the volatilization of perfumes, and to such an ex- 

 tent that beds of flowers are sometimes inodorous in the bright 

 sunlight which are fragrant in the shade. Some essences need a 

 high temperature for the production of their full effect ; while 

 others, to have their delicacy fully appreciated, require the cool- 

 ness of the evening. This principle may account for appir-fnt 

 differences of tastes among the people of different countries. The 

 odors of many substances are not of equal strength in different 

 climates. Prof. Tyndall believes that there are considerable dif- 

 ferences in the absorbing power of different odorous vapors for 

 radiant heat. He perfumed small paper cylinders by dipping them 

 by one end in an aromatic oil, and then placed them in a glass 

 tube, which communicated, through a stop-cock, with a tube in 

 which a vacuum is produced. The air, according as it has been 

 perfumed with one substance or another, discloses to the galva- 

 nometer an absorbing power, which, air at the usual pressure being 

 taken as one, varies from thirty for patchouli, to three hundred 

 and seventy-two for anise-seed. These results are, unfortunately, 

 not exact, for no account is taken in them of the tensions of the 

 odorous vapors, which certainly vary, though they are probably 

 of very small absolute value. 



Messrs. Nichols and Bailey have compared the smelling powers 

 of men and women. Having made measured solutions of a num- 

 ber of essential oils, a series of flasks was prepared so that the 

 solution in each succeeding one should be only half as strong as 

 that in the preceding one. The flasks were " shuffled/' and the sub- 

 jects of the experiment were called upon to rearrange them in the 

 order of concentration of the solutions. The smelling power of 

 women appeared to be on the whole less delicate than that of the 

 men. The extreme delicacy of the scent of the dog is well known. 

 Mr. Romanes has shown that, by fastening a sheet of paper to the 

 shoes, the odor may be masked, and the dog prevented from 

 following the track of his master ; but that a contact with the 



