SCIENCE. 



1 1 1 



brace most of the gases and vapors employed in my 

 former researches. My first source of rays was a Siem- 

 ens' lamp connected with a dynamo-machine, worked by 

 a gas engine. A glass lens was used to concentrate the 

 rays, and afterwards two lenses. By the first the rays 

 were rendered parallel, while the second caused them to 

 converge to a point about seven inches distant from the 

 lens. A circle of sheet zinc provided first with radial 

 slits and afterwards with teeth and interspaces, cut 

 through it, was mounted vertically on a whirling table, 

 and caused to rotate rapidly across the beam near the 

 focus. The passage of the slits produced the desired in- 

 termittence,* while a flask containing the gas or vapor to 

 be examined received the shocks of the beam immedi- 

 ately behind the rotating disc. From the flask a tube of 

 india-rubber, ending in a tapering one of ivory or box 

 wood, led to the ear, which was thus rendered keenly 

 sensitive to any sound generated within the flask. Com- 

 pared with the beautiful apparatus of Mr. Graham Bell, 

 the arrangement here described is rude ; it is, however, 

 effective. 



With this arrangement the number of sounding gases 

 and vapors was rapidly increased. But I was soon made 

 aware that the glass lenses withdrew from the beam its 

 effectual rays. The silvered mirrors employed in my pre- 

 vious researches were therefore invoked ; and with them, 

 acting sometimes singly and sometimes as conjugate 

 mirrors, the curious and striking results which I have 

 new the honor to submit to society were obtained. 



Sulphuric ether, formic ether, and acetic ether 

 being placed in bulbous flasks, t their vapors were 

 soon diffused in the air above the liquid. On plac- 

 ing these flasks, whose bottoms only were covered 

 by the liquid, behind the rotating disc, so that the 

 intermittent beam passed through the vapor, loud 

 musical tones were in each case obtained. These 

 are known to be the most highly absorbent vapors which 

 my experiments revealed. Chloroform and bisulphide of 

 carbon, on the other hand, are known to be the least ab- 

 sorbent, the latter standing near the head of diatherman- 

 ous vapors. The sounds extracted from these two sub- 

 stances were usually weak and sometimes barely audible, 

 being more feeble with the bisulphide than with the chlo- 

 roform. With regard to the vapors of amylene, iodide 

 of ethyl, iodide of methyl and benzol, other things being 

 equal, their power to produce musical tones appeared to 

 be accurately expressed by their ability to absorb radiant 

 heat. 



It is the vapor, and not the liquid, that is effective in 

 producing the sounds. Taking, for example, the bottles 

 in which my volatile substances are habitually kept, I 

 permitted the intermittent beam to impinge upon the 

 liquid in each of them. No sound was in any case pro- 

 duced, while the moment the vapor-laden space above an 

 active liquid was traversed by the beam, musical tones 

 made themselves audible. 



A rock-salt cell filled entirely with a volatile liquid, and 

 subjected to the intermittent beam, produced no sound. 

 This cell was circular and closed at the top. Once, while 

 operating with a highly athermanous substance, a distinct 

 musical note was heard. On examining the cell, however, 

 a small bubble was found at its top. The bubble was 

 less than a quarter of an inch in diameter, but still suffi- 



* When the disc rotates the individual slits disappear, forming a hazy 

 zone throrgh which objects are visible. Throwing by the clean hand, or 

 better still by white paper, the beam back upon the disc, it appears to 

 stand still, the slips forming so many dark rectangles. The reason is ob- 

 vious, but the experiment is a very beautiful one. 



I may add that when I stand with open eyes in the flashing beam, at a 

 definite velocity of recurrence, subjective colors of extraordinary gor- 

 geousness are produced. With slower or quicker rates of rotation the 

 colors disappear. The flashes also produce a giddiness, sometimes intense 

 enough to cause me to grasp the table to keep myself erect. 



+ I have employed flasks measuring from 8 inches to %ths of an inch in 

 diameter. The smallest flask, which had a stem with aboie of about J^th 

 of an inch in diameter, yielded better effects than the largest. Flasks 

 from 2 to 3 inches in diameter yield good results. Ordinary test-tubes also 

 answer weU. 



cient to produce audible sounds. When the cell was com- 

 pletely filled, the sounds disappeared. 



It is hardly necessary to state that the pitch of the note 

 obtained in each case is determined by the velocity of ro- 

 tation. It is the same as that produced by blowing 

 against the rotating disc and allowing its slits to act like 

 the perforations of a syren. 



Thus, as regards vapors, prevision has been justified 

 by experiment. I now turn to gases. A small flask, after 

 having been heated in the spirit lamp so as to detach all 

 moisture from its sides, was carefully filled with dried air. 

 Placed in the intermittent beam it yielded a musical note, 

 but so feeble as to be heard only with attention. Dry 

 oxygen and hydrogen behaved like dry air. This agrees 

 with my former experiments, which assigned a hardly 

 sensible absorption to these gases. When the dry air 

 was displaced by carbonic acid, the sound was far louder 

 than that obtained from any of the elementary gases. 

 When the carbonic acid was displaced by nitrous oxide, 

 the sound was much more forcible still, and when the 

 nitrous oxide was displaced by olefiant gas, it gave birth 

 to a musical note which, when the beam was in good con- 

 dition, and the bulb well chosen, seemed as loud as that 

 of an ordinary organ pipe.* We have here the exact 

 order in which my former experiments proved these gases 

 to stand as absorbers of radiant heat. The amount of 

 the absorpti n and the intensity of the sound go hand in 

 hand. 



A soap bubble blown with nitrous oxide, or olefiant 

 gas, and exposed to the intermittent beam produced no 

 sound, no matter how its size might be varied. The 

 pulses obviously expended themselves upon the flexible 

 envelope, which transferred them to the air outside. 



But a film thus impressionable to impulses on its in- 

 terior surface, must prove at least equally sensible to 

 sonorous waves impinging on it from without. Hence, 

 I inferred, the eminent suitability of soap bubbles for 

 sound lenses. Placing a "sensitive flame" some feet 

 distant from a small sounding reed, the pressure was so 

 arranged that the flame burnt tranquilly. A bubble of 

 nitrous oxide (sp. gr. 1-527) was then blown, and placed 

 in front of the reed. The flame immediately fell and 

 roared, and continued agitated as long as the lens re- 

 mained in position. A pendulous motion could be im- 

 parted to the bubble, so as to cause it to pass to and fro 

 in front of the reed. The flame responded, by alternately 

 roaring and becoming tranquil, to every swing of the 

 bubble. Nitrous oxide is far better for this experi- 

 ment than carbonic acid, which speedily ruins its en- 

 velope. 



The pressure was altered so as to throw the flame, 

 when the reed sounded, into violent agitation. A bubble 

 blown with hydrogen (sp. gr. 0-069) being placed in front 

 of the reed, the flame was immediately stilled. The ear 

 answers instead of the flame. 



In 1839, I proved gaseous ammonia to be extremely 

 impervious to radiant heat. My interest in its deport- 

 ment when subjected to this novel test was therefore 

 great. Placing a small quantity of liquid ammonia in 

 one of the flasks, and warming the liquid slightly, the 

 intermittent beam was sent through the space above 

 the liquid. A loud musical note was immediately pro- 

 duced. By the proper application of heat to a liquid 

 the sounds may be always intensified. The ordinary 

 temperature, however, suffices in all the cases thus far 

 referred to. 



In this relation the vapor of water was that which in- 

 terested me most, and as I could not hope that at or- 

 dinary temperatures it existed in sufficient amount to 

 produce audible tones, I heated a small quantity of 

 water in a flask almost up to its boiling-point. Placed 

 in the intermitten beam, I heard — I avow with delight 



* With conjugate mirrors the sounds with olefiant gas are readily ob- 

 tained at a distance of twenty yards from the lamp. I hope to be able to 

 make a candle flame effective in these experiments. 



