SCIENCE. 



— a powerful musical sound produced by the aqueous 

 vapor. 



Small wreaths of haze, produced by the partial con- 

 densation of the vapor in the upper and cooler air of 

 the flask, were, however, visible in this experiment; 

 and it was necessary to prove that this haze was not 

 the cause of the sound. The flask was, therefore, 

 heated by a spirit-name beyond the temperature of 

 boiling* water. The closest scrutiny by a condensed 

 beam of light then revealed no trace of cloudiness 

 above the liquid. From the perfectly invisible vapor, 

 however, the musical sound issued, if anything, more 

 forcible than before. I placed the flask in cold water 

 until its temperature was reduced from about 90 to 

 io" C, fully expecting that the sound would vanish at 

 this temperature; but not withstanding the tenuity of 

 the vapor, the sound extracted from it was not only dis- 

 tinct but loud. 



Three empty flasks, filled with ordinary air, were 

 placed in a freezing mixture for a quarter of an hour. 

 On being rapidly transferred to the intermittent beam, 

 sounds much louder than those obtainable from dry air 

 were produced. 



Warming these flasks in the flame of a spirit-lamp 

 until all visible humidity has been removed, and after- 

 wards urging dried air through them, on being placed 

 in the intermittent beam the-sotum in each case was 

 found to have fallen almost to silence. 



Sending, by means of a glass tube, a puff of breath 

 from the lungs into a dried flask, the power of emitting 

 sound was immediately restored. 



When, instead of breathing into a dry flask, the 

 common air of the laboratory was urged through it, the 

 sounds became immediately intensified. I was by no 

 means prepared for the extraordinary delicacy of this new 

 method of testing the athermancy and diathermancy of 

 gases and vapors, and it cannot be otherwise than satis- 

 factory to me to find that particular vapor, whose al- 

 leged deportment towards radiant heat has been most 

 strenuously denied, affirming thus audibly its true char- 

 acter. 



After what has been stated regarding aqueous vapor, 

 we are prepared for the fact that an exceedingly small 

 percentage of any highly athermanous gas diffused in air 

 suffices to exalt the sounds. An accHen'al observation 

 will illustrate this point. A flask was filled wi;h coal-gas 

 and held bottom upwards in the intermittent beam. 

 The sounds produced were of a force corresponding to 

 the known absorptive energy of coal-gas. The flask 

 was then placed upright, with its mouth open upon a 

 table, and permitted to remain there for nearly an hour. 

 On being restored to the beam, the sounds produced 

 were far louder than those which could be obtained from 

 common air. 



Transferring a small flask or a test-tube from a cold 

 place to the intermittent beam, it is sometimes found to 

 be practically silent for a moment, after which the sounds 

 become distinctly audible. This I take to be due to the 

 vaporisation by the calorific beam of the thin film of 

 moisture adherent to the glass. 



My previous experiments having satisfied me of the 

 generality of the rule that volatile liquids andtheir vapors 

 absorb the same rays, I thought it probable that the in- 

 troduction of a thin layer of its liquid, even in the case 

 of a most energetic vapor, would detach the effective 

 rays, and thus quench the sounds. The experiment was 

 made, and the conclusion verified. A layer of water, 

 formic ether, sulphuric ether, or acetic ether, ^th of an 

 inch in thickness, rendered the transmitted beam power- 

 less to produce any musical sound. These liquids being 

 transparent to light, the efficient rays which they inter- 

 cepted must have been those of obscure heat. 



A layer of bisulphide of carbon about ten times the 

 thickness of the transparent layers just referred to, and 

 rendered opaque to light by dissolved iodine, was inter- 



posed in the path of the intermittent beam. It produced 

 hardly any diminution of the sounds of the more active 

 vapors— a further proof that it is the invisible heat rays, 

 to which the solution of iodine is so eminently transpar- 

 ent, that are here effectual. 



Converting one of the small flasks used in the fore- 

 going experiments into a thermometer bulb, and filling 

 it with various gases in succession, it was found that 

 with those gases which yielded a feeble sound, the dis- 

 placement of a thermometric column associated with the 

 bulb was slow and feeble, while with those gases which 

 yielded loud sounds, the displacement was prompt and 

 forcible. 



Received January 10, 1881. 

 FURTHER EXPERIMENTS. 



Since the handing in of the foregoing note, on the 3rd 

 of January, the experiments have been pushed forward ; 

 augmented acquaintance with the subject serving only to 

 confirm my estimate of its interest and importance. 



All the results described in my first note have been ob- 

 tained in a very energetic form with a battery of sixty 

 Grove's cells. 



On the 4th of January I chose for my source of rays a 

 powerful lime-light, which, when sufficient care is taken 

 to prevent the pitting of the cylinder, works with admir- 

 able steadiness and without any noise. I also changed 

 my mirror for one of shorter focus, which permitted a 

 nearer approach to the source of rays. Tested with this 

 new reflector the stronger vapors rose remarkably in 

 sounding power. 



Improved manipulation was, I considered, sure to ex- 

 tract sounds from rays of much more moderate intensity 

 than those of the lime-light. For this light, therefore, a 

 common candle flame was substituted. Received and 

 thrown back by the mirror, the radiant heat of the candle 

 produced audible tones in all the stronger vapors. 



Abandoning the mirror and bringing the candle close 

 to the rotating disc, its direct rays produced audible 

 sounds. 



A red-hot coal, taken from the fire and held close to 

 the rotating disc produced forcible sounds in a flask at 

 the other side. 



A red-hot poker, placed in the position previously oc- 

 cupied by the coal, produced strong sounds. Maintain- 

 ing the flask in position behind the rotating disc, amusing 

 alternations of sound and silence accompanied the alter- 

 nate introduction and removal of the poker. 



The temperature of the iron was then lowered till its 

 heat just ceased to be visible. The intermittent invisible 

 rays produced audible sounds. 



The temperature was gradually lowered, being accom- 

 panied by a gradual and continuous diminution of the 

 sound. When it ceased to be audible the temperature 

 of the poker was found to be below that of boiling 

 water. 



As might be expected from the foregoing experiments, 

 an incandescent platinum spiral, with or without the 

 mirror, produced musical sounds. When the battery 

 power was reduced from ten cells to three, the sounds, 

 though enfeebled, were still distinct. 



My neglect of aqueous vapor had led me for a time 

 astray in 1859, but before publishing my results I had 

 discovered my error. On the present occasion this om- 

 nipresent substance had also to be reckoned with. Four- 

 teen flasks ol various sizes, with their bottoms covered 

 with a little sulphuric acid, were closed with ordinary 

 corks and permitted to remain in the laboratory from the 

 23d of December to the 4th of January. Tested on the 

 latter day with the intermittent beam, half of them emit- 

 ted feeble sounds, but half were silent. The sounds 

 were undoubtedly due, not to dry air, but to traces of 

 aqueous vapor. 



An ordinary bottle, containing sulphuric acid for 

 laboratory purposes, being connected with the ear and 



