654 THE POPULAR SCIENCE MONTHLY. 



termittent beam. The well-dried air within the bulbs proved silent, 

 while the slightest admixture of humid air sufficed to endow it with 

 sounding power. Placing a little water in a thin glass bulb, and heat- 

 ing it nearly to its boiling-point, the sounds produced by the developed 

 vapor are exceedingly loud. The bulbs employed in these experiments 

 are usually about a cubic inch in volume. They may, however, be re- 

 duced to one fiftieth or even one one-hundredth of a cubic inch. 

 When a minute drop of water is vaporized within such little bulbs, on 

 their exposure to the intermittent beam loud musical sounds are pro- 

 duced. 



It is to be borne in mind that the heat employed in these experi- 

 ments, coming as it did from a highly luminous source, was absorbed 

 in a far smaller degree than would be the heat from bodies under the 

 temperature of incandescence. 



To render the correlation of sound-producing power and ather- 

 mancy complete, all the gases and vapors which had been exposed to 

 the intermittent beam were examined as to the augmentation of their 

 elastic force through the absorption of radiant heat. A glass cylinder, 

 four inches long and three inches in diameter, had its ends closed with 

 transparent plates of rock-salt. Connected with this cylinder was a 

 narrow U-tube, containing a colored liquid which stood at the same 

 level in the two arms of the U. The cylinder could be exhausted 

 at pleasure or filled with a gas or vapor. When filled, the sudden 

 removal of a double silvered screen permitted the beam from the 

 lime-light to pass through it, the augmentation of elastic force being 

 immediately declared by the depression of the liquid in one of the 

 arms of the U-tube and its elevation in the other. The difference of 

 level in the two arms gave, in terms of water-pressure, a measure of 

 the heat absorbed. With the stronger vapors it would be easy with 

 this instrument to produce an augmentation of elastic force corre- 

 sponding to a water-pressure of a thousand millimetres. As might be 

 expected, the intensity of the sounds corresponded with the energy 

 of the absorption, varying from " exceedingly strong," " very strong," 

 " strong," " moderate," " weak," to " inaudible." In this connection 

 reference was made to the interesting experiments of Professor Rontgen, 

 an independent and successful worker in this field. 



In conclusion, the lecture draws attention to the bearing of its' 

 results upon the phenomena of meteorology. The views of Magnus, 

 regarding the part played by mist or haze, are referred to, and atten- 

 tion is directed to various observations by Wells, which are in opposi- 

 tion to these views. The observations of Wilson, Six, Leslie, Denham, 

 Hooker, Livingstone, Mitchell, Strachey, and others are referred to and 

 connected with the action of aqueous vapor upon solar and terrestrial 

 radiation. Many years ago the lecturer sought to imitate the action 

 of aqueous vapor on the solar rays by sending a beam from the electric 

 light through a layer of water, and afterward examining its spectrum. 



