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MMI 
 
 ^ v.. • ► ■ *' 
 
 UPON THK 
 
 PRODUCTION OF SOUND BY RADIANT 
 
 ENERGY. 
 
 t 
 
 ^' 
 
 By Alexander Graham Bkij,, 
 
 [A Paper read before the National Aoadeniyof Scieuoea, April, '21, 1881. J 
 
 In a paper read hefore tlie Aineriiian Assoriatioii fur t!ie 
 Advancement of Science, lust AugUHt, I described certuiii ex- 
 perimentH made l»y Mr. Sumner Tainter and myself which had 
 resulted in the construction of a " Photophone^'' or apparatus 
 for the production of sound by light;* and it will he my oh- 
 je(!t to-day to descrrihe the progress we have made in the inves- 
 tigation of photophonic phenomena since the date of this com- 
 munication. 
 
 In my Boston paper the disciovery was announced that thin 
 disks of very many different substances emitted sounds when 
 exposed to the action of a rapidly-interrupted beam of sunlight. 
 The great variety of material used in these experiments led me 
 to believe that sonorousness under such circumstatices would be 
 found to be a general property of all matter. 
 
 At that time we had failed to obtain audible effects from 
 masses of the various substances which became sonorous in the 
 condition of thin diaphragms, but this failure was explained 
 uf>on the supposition that the molecular disturbance produced 
 
 * FroceediugB of Aiuerioau Awooiatiou for the Advanoement of Science, 
 Aug. 27th, 1880; see, also, American Jonniol cf Science, vol. xx, p. 3or>; 
 Journal of the American Electrical Society, vol. iii, p. 3 ; Journal of the 
 Society^ of Telegraph Engineera and Electriciaas, vol. iz, p. 401 ; Annalea de 
 Ghimie'et do Physique, toL xxi. 
 
 ■J. a 
 
 ji-ii^ 
 
Ii.v till' li^lif wiiH I'liirrty II Kiirfiico iicfiun, iitid timt iiikIci' t\w 
 (•in lllll^lllll(•»'^ i>f tlic cxixTinit'iith tlic vilinitioii liml tu lie fniiiK- 
 iiiittc.l tliniiijili tilt iiuiKH <il' tlif sul)hfaiifi' iiMMtk-r tu ivrtfct tho 
 far. It WHS tlicrcfurt? HU|)j».mi'(l that, if wo (oiild Iciul to tlic our 
 air tiiat was <iircctly in coiitiu-t with tlu' illiiiiiiiititcci Hiirfacc, 
 loialcr suiiikIh iiii^ht !>(> i^htaincd, and solid niassfK lie fuiind to 
 he as siiMnruus as thin diai)l!rai^nis. The first I'Xju'riiiicnts niiidc 
 til vcritv this hvpothcsis jMtintt'd towards sncci-ss. A hciim of 
 sunlight was fot-nswi'd into (nic i-nd of un ojmmi tnltc, tho car 
 lichi"^ j)lac('d at tho other <'nd. Ujmhi intrrrni>tin;^ the lu'iun, a 
 dear, nnisical tone was heard, the pitch of which de])eiided upon 
 the fre([nency of the iiiterriij)tion of the lijiht an<l the hmdnosa 
 upon the inateriiil coni])osin^ the tidie. 
 
 At this stuf^c onr experiments were interrupted, as cinMiiu 
 stances called ine to Knro]>e. 
 
 While in I'arin a ni'w form of th(> experiment occurred to 
 my mind, which wotdd not only enable us to investipite the 
 sounds ])rodueed hy manses, hut would also permit ns to test 
 the njore general proposition that HonoroiixnexH, ntnliir th<'. in- 
 HidiKi. of intvrinittrid lii/ht, ix a projhrtifi'oiiiiiioii to (til inntler. 
 
 The sid)stance to lie tested was to he placed in the interitir 
 of a transparent vessel, made of some material which (like ghiss) 
 is transparent to light, hut practically oj^ayue to sound. 
 
 Under such circumstances the light (rould get in, hut the 
 sound priuluced hy the viltration of the suhstance <'ould not get 
 out. The audible effects coiild be studied by placing the ear 
 in communication with the interior of the vessel hy means of a 
 hearing tid)e. 
 
 Some preliminary experiments were nuidc in Paris to test 
 this idea, and the results were so promising that they were eom- 
 niunicated to the PVench Academy on the 11th of October, 1880, 
 in a note read for me l>y M. Antoine IJreguet.* Shortly after- 
 wards I wrote to Mr. Tainter, suggesting that he should carry 
 on the investigation in America, as circumstances prevented 
 me from doing so myself in Europe. As these experiments 
 seem to have formed the common starting point for a series of 
 independent researches of the most inaportant character, car- 
 • Compter JienduM, vol. xcl, p. 595. 
 
 ■%^, 
 
 *■*■■■-■' --'"1 ■'- 
 
1 
 
 "idcr f|,„ 
 '" •'«' fnitiH- 
 
 ••iffivt the 
 ' to flic car 
 Niirfiicc, 
 "• i'*>mnl to 
 "'"fs iimdo 
 ^ licaiii of 
 "'i fli(^ ciir 
 '•' Im'uiii, h 
 "•l<'<l upon 
 •' loiidncHH 
 
 i"^ <'ir(!iiiii 
 
 •••IIITC'd to 
 
 i^'iite tlio 
 iiK to tost 
 
 ''V M-; i„. 
 
 fl 'nutter. 
 
 t' interior 
 
 ik 
 
 »' glllHs) 
 
 d. 
 
 > '>nt tho 
 J not get 
 ' fill! ear 
 
 '••1118 of u 
 
 « to test 
 
 il'C (iOIll- 
 
 I-, 1880, 
 y after- 
 d carry 
 'vented 
 inients 
 ries of 
 'J", car- 
 
 8 
 
 rie<l on Kiinnltam oii.^ly, in Atiicririi liy Mr. Taintcr, ii)id in 
 Knro|)f liy M. Mcn-iidicr,* I'rof. TyniialKt W. K. Konttr«'n4 
 iind W. II. i'ntrc, .-^ I iiiny lie pcrniitted to (|ii(it»' liniii my 
 letter to Mr. Taintcr llic |>a.ssaj;c dcM-riiiinj; the c,\|)erinientH 
 referred to: 
 
 " MhTkoi'oi.rpAN UoTKi., RuK Camiion, Pakih, 
 
 " Nor. 2, 18S0. 
 " Dkak Mk. Taintkk : 
 
 • * * "I liuve devised a inetliof! td' ]»rodiicinir suiinds liy 
 " the action of an intermittent lieam of lij;ht from suhstaiices 
 " that eaimot lie olitaincd in the shape of thin diaphra^'ins or 
 " in the tnlmlar furni ; indeed, the method is specially adapted 
 " to tchtin;; the jrencralily td' the phenomenon we havti discov- 
 " ered, as it can lie adajite 1 to solids, li(jiiids, and j^ases. 
 
 " Place the sidistaiK-c to he experimented with in a j^lass test- 
 " tnlie, (Miimect a rnlihcr tuli(( with the month of the test-tnlie, 
 " jilacinj^ tli(' other end of the pipe to the ear. Then focns 
 " the intermittent lieam npuii rhe siilistaiice in the \\\W\ I have 
 " tried a lariic numlier of sidistances in this wav with lireat 
 " success, althoiii^h it is extremely ditlicnlt to i;et a jrlimpsc! of 
 " the sun here, ami when it does shine the intensity of the li;;lit 
 " is iHit to lie compared with that to lie ohtained in Wasliin^- 
 " ton. I <;ot splendid etfccts fnnn crystals of liichromate of 
 " potash, ci'ystals of sid])hate of coppei', ami from t<iliacco 
 "smoke. A whole ci<;ar jilaced in tlie test-tnlic ]irodnced a 
 " very loud sonnd. I coidd not hearanythiny from plain wafer, 
 " lint when the water was discolored with itd< a feelile sonnd 
 " was heard. 1 would suf^j^est that you nnjjht rejieat these ex- 
 " periments and extend the residts," »fee., »&e. 
 
 lU'perinicatK with SoUila. 
 
 Upon my return to Wasliin<j;ton in the early part of ., !'uary,|] 
 Mr. Taintcr communicated to me th(> results of the expe 'nuMits 
 he had made in my lalioratory during my alisence in Europe. 
 
 * " Notes ou liadinphony," Cimpten Rendm, Die. (! and 13, IHHO; Feb. 21 
 and 28, 1881. See, hIho, Journ<i.l (le I'/ii/m'qiif, vol. x, p. ",;}. 
 
 + " Action of nn Intermittent Heiiin of UadiHiit H<!at upon OaseouB Mailer.'' 
 I'roc. Royal Siteiety, Jiiu. 13, 1881, vol. xxxi, p. 307. 
 
 X "On the tones which ariKe from the intciriiiittunt illumination of a giiH." 
 8e»! AnnaUn der I'liyn. und Vhemic, Jan., IKSi, No. 1, p. l.'i.'). 
 
 § " On tho Conversion of Radiant Energy into Sonoroiis Vibrations." Proc. 
 Royal Society, March 10, 1881, vol. xxxi, p. .'ilMi. 
 
 II On the 7th of January. 
 
Hi' liiul ('i»imr.t!ii('C(l )>.v oxiiiniiiing the sonorous proportien of 
 ii vast iiiiiiil>t'r of suhstaiiccfi oiicloBcd in tost-tul»es in u simple 
 ciiipiriciil Hoareh for loud effec^ts. He was tlius led {rrachiHlly 
 to the discovery that cotton-wooi, worsted, silk, and tibrous 
 materials jreiierally, produced mu('h louder soimds ti\an hard 
 rijfid iKKJleslike crystals, or diaphragms such as we had hitherto 
 used. 
 
 In order to study the effects under better circumstances he 
 eu'-losed his materials in a conical cavity in a piet^e of lirass 
 dosed Ity a Hat phite of ghiss. A iirass tul)e leading into the 
 cavity served f<»r connecti(»n with the hearing-tuhe. When 
 this conical cavity was stuffed with worsted or other iibrous 
 material- the so\mds produced were nuich louder than when 
 a test-ti.oe was employed. This form of receiver is shown in 
 Fig\ii'e I. 
 
 Mr. Tainter next collected silks and worsteds of diiferent 
 colors, and speedily four.d that the darkest shades prodiiced the 
 liest effects. Black worsted especially gave an extremely loud 
 
 sound. 
 
 As white cotton-wool had proved itself equal, if not superior, 
 to any other white til)rous material before tried, he was anxious 
 to obtain (!olored specumens for comparison. Not having any 
 at hand, however, he tried the effect of darkeiung some (;otton- 
 wool with himp-black. Such a marked reinforcement of the 
 sound residted that he wks induced to try lamp-black alone. 
 
 About a teaspoonful of lamp-ldack was placed mi a test-tube 
 and exposed t<t an intermittent beam of sunlight. The sound 
 prodaced was much louder than any heard befor 
 
 Upon smoking a piece of plate-giass, and holding it in tl e 
 intermittent beam with the lamp-ldack surface towards the sun, 
 the sound produced was loud enough to be heard, with atten- 
 tion, in any part of the room. With the lamp-l)lack surface 
 turned from the sun the; sound was nnurh feebler. 
 
 Mr. Tainter repeated these experiments for me immediately 
 upon my return to Washington, so that 1 might verify his 
 results. 
 
 Upon smoking the interior of the conical cavity shown in 
 Figure 1, and then exposing it to fh^ intermittent beam, with 
 
 l» 
 
 umin 
 
 t m i> iiti »iw *« 
 
^ 
 
 us propcrfie« of 
 l»f'H ill u siiiiple 
 « I«'d j-'nuhmlly 
 !•<, fuid fil)roii8 
 inlri than Jmrd 
 ive hud liitliertu 
 
 MuuKtiiniieH lie 
 )iece of l.rasH 
 adiufr into tJie 
 :-tul»t'. Wlion 
 other flln-oiLs 
 ler than wlien 
 Gi" is shown in 
 
 8 of different 
 
 produced the 
 
 xtrenielj loud 
 
 not superior, 
 WHS anxious 
 't havin-r -.my 
 ' some cotton- 
 ^'luent of the 
 fick alone. 
 'H a test-tube 
 Tli<) sound 
 
 »K it in t}e 
 iirds (he sun, 
 J with atten- 
 Ijick surface 
 
 iinmediatelj 
 t verify his 
 
 ^J shown in 
 heani, witlj ^ 
 
 mhMI 
 
 the {jjlass lid in position as shown, the effect was jjorfectlj' 
 startling. The soinid was so loud as to be actually painful io 
 an ear placed doseiy against the end of the hearing-tube. 
 
 The sounds, however, we.e sensibly louder when we j)laced 
 some smoked wire gauze in the receiver, as illustrate'l in the 
 drawing, Figure 1. 
 
 When the beam was thrown into a resonator, the interior of 
 which had been smoked over a lamp, most curious alternations 
 of sound and silence were observed. The interi'uiiting disk 
 was set rotating at a high rate of speed, and was then allowed 
 to come gradually to rest. An extremely feeble nuisical tone 
 was at first heard, which fell in pitch as the rate of interrup- 
 tion grew less. The loudness of the sound produced varied in 
 the most interesting manner. Minor reinforcements were con- 
 stantly occurring, which became more and more marked as the 
 true pitch of the resonator was neared. When at hist the fre- 
 quency of interruption corresponded to the fre(iuen((y (jf the 
 fundamental of the resonator, the sound was so loud that it 
 might have been heard by an audience of lumdreds of people. 
 
 The effects produced by lamp-l)lack seemed to me to be \ery 
 extraordinary, especially as 1 had a distinct recollection of ex- 
 periments made in the summer of 1880 with smoked diaphragnis, 
 in which no such reinforcement was noticed. 
 
 Upon examining the records of our past photophonic experi- 
 ments we found in vol. vii, p. 57, the following note: 
 
 " Experiment V. — Mica diaphragm covered with lamp-blat^k 
 on side exposed to light. 
 
 "Result : distinct tound about same as without lampblack. — 
 A. G. li., July \m, 1880. 
 
 "Verified the above, but think it somewhat louder than 
 when used without lamp-black." — S. T., July 18th, 1880. 
 
 Upon repeating this old experiment we arrived at the same 
 result as that noted. Little if any augmentation of sound re- 
 sulted from smoking the mica. In this expenment ti»e effect 
 was observed by placing the mica diaphragm against the ear and 
 also by listening through a hearing-tube, one t'vA of whi.'h was 
 closed by the diaphragm. The sound was found tt> be more 
 
 ""'Mil K 
 
! * 
 
 i I 
 
 I !i 
 ■ 11 
 
 r> 
 
 aiidililc through the froo air when t)»e car was placed as near 
 to the hini|) hhirk surface as it cduld l»e Itroiiirht without 
 hIuvUii"? it. Tlius the vihratious produced in hunp-hhic'v under 
 tile aliove circumstances do not appear tti he comnuinicated to 
 any very appreciahle extent to the diaphra<;ni on which the 
 lanip-ldat^ii is deposited. 
 
 At tlie time of my comnnmi< ation to the American Associa- 
 tion I had lieen unaitki to satisfy myself that the substances 
 which had 'oecome sonorous under the direct influence of inter- 
 inittent sunlij^ht \v(4'e caj>altle <tf reproduciniij the sounds of 
 articidate speech under tlie action of an undulatory heam from 
 our i)hotophonic transmitter. The difliculty in ascertaining 
 this will he \niderstood i)y considering that the sounds emitted 
 hy thin diapiiragms and tuhes were so feeble that it was im- 
 prac,tical)le to produce audible cirects from substances in these 
 conditions at any considerable distance from the transmitter; 
 but it was e(jually injpctssible to judge of the effecrts produced 
 by our artimlate ti'ansmittei* at a short distance away because 
 the speaker's voice was directly audible thntugh the air. The 
 extremely loud sounds pnxluced from lamp-black have enabled 
 us to demonstrate the feasibility of using this suiistance in an 
 articulating photophone in phice of the electrical receiver for- 
 merly employotl. 
 
 The drawing (Fig. 2) illustrates the mode in which the experi- 
 ment v,'as conducted. The diaphragm of the transmitter (A) 
 was only 5 centimetres in diameter, the diameter of the re- 
 ceiver (B) was alao 5 centimetres, and the distance between the 
 two was 40 metres, or 800 times the diameter of the transmit- 
 ting diaphrtigm. We were unable to experiment at greater 
 distances without a heliostat on account of the ditiiculty of 
 keeping the light steadily directed on the receiver. Words 
 and sentences spoken intt) the transmitt"r in a low tone of voice 
 were audibly reproduced by the lamp-black receiver. 
 
 In Fig. 8 is shown a mode of interrupting a beam of sunlight 
 for producing distant etfet-ts without the use of lenses. Two 
 similarly-perforated disks are employed, one of which is set in 
 rapid rotation, while the other remains stationary. This form 
 of interrupter is also admirably atlapted for work with at tiflcial 
 
 JSkm 
 
iicofl as near 
 d>t without 
 -1>1}ica uiidfr 
 rn.nicated to 
 1 which tlio 
 
 'an Associa- 
 ' wiil).stan(!e8 
 we of iiiter- 
 i sounds of 
 
 heani from 
 iscertairiinij 
 lids emitted 
 
 it was iin- 
 ^'08 in these 
 ransiniiter; 
 9 prodneed 
 ay because 
 ! air. T)ie 
 ve enabled 
 ance in an 
 eeiver for- 
 
 the experi- 
 tnitter (A) 
 af the re- 
 tween the 
 transmit- 
 ■t greater 
 Hculty of 
 Words 
 3 of voice 
 
 ■ sunlight 
 Js. Two 
 I is set in 
 'his foi-in 
 a'tificial 
 
 
■■■i* 
 
MM 
 
 ■m 
 
 11 
 
 lif^ht. The receiver illuKtriited in the druwirif^ ooiisiHtH of a 
 piirulxilic! reflector, in the focnis of which i^ i)hu^e(i a j?hi8H ves- 
 Kci (A) contiiinin^ lainj>-l)hick or other sensitive suitstance, and 
 connected with a l.earing-tuhe. The heain of light is inter- 
 1 ii])ted l»y its passage tln'oiigli the tw(» sh>tted disks shown at H, 
 and in operating the instnnnent nuisical sigc.als like the <lots 
 and ilashes of the Morse ali)hal)et arc produced from the scMisi- 
 tive receiver (A) l>y sliglit motions of the mirror (C) a1»out its 
 axis (I\) 
 
 In place of the parabolic refle(^tor shown in the tigure a ironi- 
 cal reflector like that recouunended !)y Prof. Sylvanus Thomp- 
 son* can he used, in which case acylintlrical glass vessel would 
 he preferaltle to the flask (A) shown in tlu^ flg\n'e. 
 
 In regard to the sensitive materials that can be employed, 
 our experiments indicate that in the case of solids the physical 
 condition and the color markedly influence the intensity of 
 the sonorous effects. Tlte loadesl mionh are pyodiicet/ from 
 snhxtances in a loose, porous, sjHuxjy condition, and from those 
 that have the darkest or most ahsorhent colors. 
 
 The materials from which the host effects have been obtained 
 are cotton-wool, worsted, fibrous materials gene^'ally, cork, 
 sponge, platinum and other metals in a spongy condition, and 
 lamp-black. 
 
 The loud sounds produced from such substances may per- 
 haps be explained in the following matnier: Let us consider, 
 for example, the case of lamp-black — a substance which be- 
 comes heated by exposure to rays of all refrangibility. I look 
 upon a mass of this sulistance as a sort of sponge, v.ith its pores 
 filled with air instead of water. When a beam of sunlight 
 falls upon this mass, the particles of lamp black are heated, and 
 consequently expand, causing a contraction of the air-spaces 
 or pores among them. 
 
 Under these circumstances a pulse of air shoild be expelled, 
 just as we would squeeze out water from a sjxinge. 
 
 The force with which the air is expelled nuist be greatly in- 
 
 ' (!reased by the expansion of the air itself, due to contact with 
 
 the heated particles of lamp-black. When the light is cut off 
 
 ♦Phil. Mag., April, 1881, vol. xi, p. 28(). 
 
 ffi^^ ^p^igjaig^^i!i«5jalia»a^^^ieai 
 
 t; 
 
12 
 
 •li- 
 
 the converse procews tiikcR pliico. The liunp-l)la«:k particloH 
 cool iintl contract, tlnis enlarging; the air Kpaces among them, 
 an<l tlie enehjwed air alno hecoinett co(tl. Uncier these circum- 
 stancert a partial vacuum shouM lie formed among the particles, 
 and the (jiit-jde air would tiien he altsorhed, as water is hy a 
 spougci when the pressure of the hand is rem«)ved. 
 
 I imagine that in some such manner its this u wave of con- 
 densatiim is started in the atmosphere eacli time a beam of sun- 
 light falls upon lamp-hhu^k, and a wave of rarefaction is origi- 
 nated when *he light is cut off. We ain thus uiniei'dani/ 
 liow it iif that a suhntdiice like liiiiip-hlnek pi'txhirett intense 
 sonoruits aibrationn in the iturroiindinij di/', while tit the sn/ne 
 tim£ it emnimtnieates a very feehle vihrtition to the iliivphrngm 
 or Kolid bed upon which it rests. 
 
 This (uirious fact was independently observed in England ity 
 Mr. Preecie, and it led him to ([uestion whether, in our experi- 
 ments with thin diaphragms, the sound heard was due to the 
 viliratioii of theilisk or (as Prof. Hughes had suf^gssted) to the 
 expansion and contraction of the air in contuct «• ith the disk 
 confined in the cavity behind the diaphragm. In his paper read 
 before the Royal Society on the lOth of March, Mr. Preece de- 
 scriltes experiments from which he claims to have proved that 
 the effects are wholly due to the vibrations of the contined air, 
 and that the disks Uoxjmi 'iuhrtite ui nil. 
 
 I shall briefly state my reasons for disagreeing with him in 
 this conclusion : 
 
 \ 
 
 ^ 
 
 1. When an intermittent beam of sunlight is focnssed upon 
 a sheet of hard rubber or other material, a nuisical tone can l»e 
 heard, not (mly by placing the ear inmiediately behind the part 
 receiving the lieara, hut by placing it against any portion of the 
 sheet, even though this may be a foot or more from the place 
 acted iipon by the light. 
 
 2. When the beam is thrown upon the diaphragm of a " Blake 
 Transmitter," a loud musical tone is produced by a telephone 
 connected in the same galvanic circuit with the carbon button, 
 (A,) Fig. 4. Good effects are also produced when the carlxm 
 button (A) forms, with the battery, (B,) a portion of the pri- 
 mary circuit of an induction c<»il, the telephone (C) being 
 placed in the secondary circuit. 
 
 l il JUUimiu :- 
 
^ 
 
 parti«-lofl 
 Boiifv them, 
 rte <^ir<Muii- 
 piirticli's, 
 '1" IH I)y a 
 
 e of (fon- 
 
 nil of 81111- 
 
 i« origi- 
 
 >i<ft;t'Kt.,i)i(/ 
 
 i'f< intense 
 
 the unine 
 
 <iphi'iHjm 
 
 i;1hm(1 |»y 
 ir oxpeii- 
 iie to tlie 
 5d) to the 
 
 tlie disk 
 ipei- read 
 ceeee de- 
 ved tlmt 
 ined air. 
 
 I liiin 
 
 m 
 
 id upon 
 can he 
 he part 
 1 of tlie 
 e pla(!e 
 
 'Bhike 
 
 sphone 
 
 mtton, 
 
 ^arhon 
 
 e pri- 
 
 being 
 
 i 
 
 mmmmmmmm 
 
I I 
 
 !<! 
 
 ¥ 
 
 riiilHii 
 
f-i 
 
tammmmmmmmmmmmmtm 
 
^ 
 
 M 
 
 In tlu'M' CIIM'S tin- WniMlfll ll(»\ tllltl ll|IMltll-|)i<'<-0 of f|u« trilllH- 
 
 iiiittor hlioiilil l)f rniKivcd, Hotliii' im iiir ciiviticH may l>«> left on 
 citln-r hific nf tlic iliii|ihriini. 
 
 // In t rii/rtif, fln'i'i'fiiri', tlint in tlir mm of thtii tl'isltH n rml 
 r'lhi'tiflnii of till' tlliifthi'tiifiii is ini/ti'i/ /ii/ thr iirtion of tin' iii- 
 ti'riiiifti lit hi'iiin, iiiilijMiiili nth/ of mti/ <:i-/niiii<ioii uml rontnir- 
 tloii of thv air roit^ft'iifi/ in thi' rui'ifif hiliiinl tin' ilin/thrtn/ni. 
 
 Lonl Iliiylci^h Iihh hIimwm iniitlitMniitic'iilly tliiit u t<>-iin<i-fi'<> 
 \ iliration, nf hutticicnt tiniplifiiilr to |>r<Mluco im liiMlililc Hoiirxl, 
 would rcsnit from a |>(>i'ioi|iral commuMication and altntraction 
 of heat, and lie ways: "We may coiiclnilf, I lldiik, tliat tlicrc 
 " Ih at jtrrHcnt no rcahon for <lis4-ardiii^ flKi ohvionHoxplanation 
 " tlmf thr hoiiikIh in (piCHtion iiro due to tlic Ix-ndiiij; of \\\v 
 " phifos inidpr imci|nal licatin^." (Nature, xxiii, j». 274.) 
 Mr. I'rPfct', however, seeks to prove tliat the .sonorous effects 
 (;iUniot l)(^ exphtiued upon tliis su])position ; hut his experimental 
 datii are not sutticient to support his eonelusion. Mr. I'reeei^ 
 fxpeeted that if Lord Ilaylei«i;irs explanation whs eorrecrt, the 
 expansion and eontraetion of a tliiii stri]> under the intluenee 
 of an intermittent lieam could Ite caused to open and closu a 
 ^Hlvani<^ circuit ho as to prcMluce a musical tone from u tele- 
 phcme in tiie circuit. Hut this wuh an inade(pnite way to test 
 tlie point at issue, for Lord Ilavleijjli has sh(»wn (Proc. of Roy. 
 So(\, 1n77) that an aiidiMe sound t^m l»e produced liy a vilira- 
 tion whose amplitude is /r.v.v t/mn a trn-niilliont/i of n ccntinu;- 
 trn, and eortaJidy such a vil»rati(Hi as that w(Mild not have suf- 
 ficed to operate a " nuike-and-hreak (rontai^t" like that used hy 
 Mr. I'reece. The nej^ative results ohtained l>y him (!atmot, 
 therefore, l>e considered (uaiclusive. 
 
 The following experiments (devised hy Mr. Tainter) have 
 s;iven results decidedly more favorahlo to the theory of Lord 
 Riiyk'if^h than to that of Mr. Preece : 
 
 1. A strip (A) similar to that used in Mr. Prcece's experi- 
 ment was attached firmly to the centre of an iron <liaplira>^m, 
 (li,) as shown in Fij^ure 5, and was then pulled taut at rii^ht 
 angles to tlie plane of the diaphragm. When the intermittent 
 heam was focussed npon the strip (A) a clear musical tone 
 could 1)0 heard l)y applying the ear to the heariug-tuhe (C.) 
 
 
uuu 
 
 fi 
 'I 
 
 if ■, 
 
 ;i: 
 
 
 18 
 
 77i!,s K''<iiii</ til iixlii'Kfc it I'lipUl I'.rjxinKiiin miil Ciniti'iicfiini of 
 till siihxtiiiiiw iniil''r ti'iiil . 
 
 l>iit a vilmitioii of \\\v (liaplira^fin (H) would also have re- 
 sulted if the thin strip (A) had ae(jiiirc<l a to-aiid-fro motion, 
 (ine eitliiT to the direct impact of the Iteam or to the sudden 
 exjiansiou of the air in contact with the strip. 
 
 'J. To test whether this had lieen the casr'an additional strip 
 (1)) was attached Ity its central point oidy to the ftrip under 
 trial, and was then suhniittcd to the action of the heani, as 
 shown in Fif;. 0. 
 
 It was presuiiKMi that if the vi'tration of the dia|)liraj;ni (IJ) 
 had heen due to a pnxlinHj funv actiufj; on the strip (A,) 
 that the addition of the strip (D) would not interfere with 
 the effect. Jiut if, on the other hand, it had l>eeu due to the 
 loni;iladiiial expansion and contraction of the strip (A,) the 
 sound would cease, or at least he reduced. The heam of light 
 fallini: upon strip (D) was now interrupted as l)efore hy the 
 rapid rotation of a perforated disk, which was allowed ti» come 
 frntdually to rest. 
 
 No sound was heard except in<^ at a certain speed of rotation, 
 when a feehle miisicai tone hecanie audihle. 
 
 This result is conHrmatory of the iirst. 
 
 The audi!)ility of the effect at a parti-.tular rate of interruption 
 siiiif^ests the exp'uiiatiiUJ that the strip I) had a normal rate 
 of viiiration of its own. 
 
 When the frecjnency of the interruption of the lij^ht corres- 
 |toiided to this, the strip was prohaldy throwji into vibration 
 after the maimer of a tuning-fork, in which case a to-aiid-fro 
 viiiration would i)e propagated down its stem or eentral support 
 to tlu' stri]> (A.) 
 
 This indirectly proves the value of the experiment. 
 
 The list of solid suhstances that have I)cen sui)mitted to 
 experiment in my lahoratory is t(»o long to he (pioted here, and 
 I shall merely say that we have not yet found one solid hody 
 that has failed to become sonorous under proper conditions of 
 experiment.* 
 
 Kxperhiunts init/i Llijii'ids. 
 The sounds produced by lifpiids are much more ditlicidt to 
 
 * (>Hrli(Mi and Uiiii iiiiuroNcope glasH are lutiutioiiud in my HoNtoii papur ati 
 ii")ii-resjK)UHiv«'. and po vdored chlorate of potaah iti the coniiiiuniuatioii to the 
 Fretu'li Academy, (CompteK ItenduK, vol. xcl. p. .lilS.) All theso HiiliNtaiicbH 
 Uavo Hiiiuti yielded tiouDdH under uiure carulul couditiouH of experiment. 
 
iH 
 
 <'<»i(i'it,tiint of 
 
 iilsi) havi' ri- 
 -tVo iiKtfioii^ 
 
 • fill' 8II(I(1»-J1 
 
 lifioiial Kfrip 
 ■ fi'ip iiiidfr 
 fJu' hffini, as 
 
 •I'lira^nii (U) 
 f f^trip (A,) 
 tl'l-flTC with 
 
 " 'Ino t<» tJic 
 '•'P (A,) the 
 I'iiiii of litpjif 
 of ore |,y the 
 
 WCi\ to COIIIO 
 
 of rotation, 
 
 iiitfrniption 
 'oriiial rate 
 
 i>ht correH- 
 <> vihratiori 
 I t«>-;iii(l-fi-o 
 ti'ul support 
 
 t. 
 
 I'lnitted to 
 ' Ifi'i-e, and 
 
 M>li(] |„„iy 
 
 "litioDH of 
 
 ffifiilt to 
 
 "1 paper hh 
 itioii to the 
 Hii'mtaiices 
 tueut. 
 
 19 
 
 observe than thorte produced l»y Holids. The hij^h altworptive 
 power poHsessed hy most li(]uidH would lead one to expect in- 
 tense viltrations from the action of intermittent light, hut the 
 nnniher of sonorous liquids that have so far been found is ex- 
 tremely limited, and the soun<ls produced are so feelde as to 
 be heard only by the greatest attention and under the i»est cir- 
 cumstances of experiment. In the experiments made in my 
 laboratory a very long test-tube was filled with the liipiid under 
 examination, and a flexible rubber-tube M-as slipped over the 
 mouth far enough down to prevent the possibility of any light 
 reachijig the vapor above the surface. Precautions were also 
 taken to prevent rertectictn from the bottom of the test-tube. 
 An intermittent beam of sunlight was then focussed upon the 
 li<juid in the nud<lle portion of the test-tube by means of a lens 
 of large diameter. 
 
 licsiUts. 
 Clear water No so'ind audible- 
 Water discolored by ink Feeble sound. 
 
 Mercury No sound heard. 
 
 Sidphuric ether* Feeble, but distinct sound. 
 
 Ammonia " " " " 
 
 Animonio-sulphate of copper " " " " 
 
 Writing ink " " " " 
 
 Indigo in sulphuric acid " " " " 
 
 Chloride of copper* " " " " 
 
 The liquids distinguished by an asterisk gave the best 
 sounds. 
 
 Acoustic vibrations are always much enfeebled in passing 
 from liijuids to gases, and it is prol)able that a form of experi- 
 ment may l»e devised which will yield better results l)y com- 
 municating the vil)rations of the Ii(piid to the ear through the 
 medium of a solid rod. 
 
 Ki'pcri lite ids with Gaseous Matter. 
 
 On the 29th of November, 1880, I had the pleasin-e of 
 showing to Prof. Tyndall in ihe laboratory of the Royal Insti- 
 tution the experiments described in the letter to Mr. Tainter 
 from which I have quoted above, and Prof. Tyndall at once 
 
20 
 
 (ixprt'Hsed the opinion lliat the Konnrls were due to rupid 
 ('liiin<jes of teinj)er!ituro in the Imdy submittod to the at-tion of 
 the heuin. Findin<j that no experiments Imd been made at that 
 time to test tlie sonoi-ouK propertieR of different pisen, he sng- 
 •jested filling; one te8t-tul>e with the vapor of Kidphiiric ether, 
 (a ijood alisorltent of heat,) and another with the vapor of bi- 
 sidphide of carbon, (a poor al)fiorbent,) and he predicted thai if 
 any sf)un(i wan heard it would be louder in the former case than 
 in the latter. 
 
 The experiment was innnediately made, and the result veri- 
 fied the prediction. 
 
 Since the publication <»f the memoirs of Rontjijen* and Tyn- 
 dall t we have repeated these experiments, and have extended 
 the in(|uiry to a miniber of other gaseous bodies, obtaining in 
 every case similar results to those noted in the memoirs re- 
 ferred to. 
 
 The vapors of the following substances were found to be 
 highly sonorous in the intermittent beam: Water vapor, coal 
 gas, Hulphurii! ether, alcohol, ammonia, amylene, ethyl bromide, 
 diethylamene, mercury, iodine, and peroxide of nitrogen. The 
 loudest sounds were obtained from iodine and peroxide of 
 
 introgcn. 
 
 I have now shown that sounds are produced by the direct 
 action of intermittent sunlight fr(»m substances in every physi- 
 cal condition, (solid, licpiid, and gaseous.) and the probability 
 is therefore very greatly increased that sonorousness under sucrli 
 circumstaiH^es will be found to be a universal property of 
 matter. 
 
 [Iptin Sixhatitiitcs for Seleniaiu in Kleetnenl Receivers. 
 
 At the time of my connnunication to the American Associa- 
 tion the kuidest effects obtained were produced by the use of 
 st'leuium, arranged in a cell of suitable construction, and placed 
 in a galvanic circuit with a telephone. Upon allowing an in- 
 termittent beam of sunlight to fall upon the selenium a musical 
 
 • Ann. der Phys. iind Chem., 1881, No. 1, p. lf>5. 
 t I'roc. Roy. Sec, vol. xxxi, p. 307. 
 
 1 !! 
 
 1 
 iJL 
 
 (. 
 
e to rfipid 
 )e action of 
 lade iit that 
 
 SeH, liC 8Ug- 
 
 iiiric ether, 
 upor of l)i- 
 ctt'd thai if 
 r I'Rue than 
 
 result veri- 
 
 * and Tyn- 
 3 extended 
 itaining in 
 lemoii's re- 
 
 )nnd to be 
 'apor, coal 
 1 hroinide, 
 ,'en. The 
 jroxide of 
 
 the direct 
 ery physi- 
 rol (ability 
 nder hucIi 
 :)perty of 
 
 I vet's. 
 
 i Associa- 
 lie use of 
 iid placed 
 ig an in- 
 i iniisical 
 
■ mill , ^ - ■■■ 
 
 hi 
 
 fS 
 
 fin 
 
 I 
 
 M*«^^k^i*a 
 
 I 
 
 Pisr- 7. 
 
 /^a 
 
23 
 
 tone of great intensity was produeod from tlie telephone con- 
 nected with it. 
 
 But the weleniiun was very inconHtant in its action. Two 
 pie<'ert of seleniinn (even of the same Bti<^l<) seldom yielded the 
 sami' resnlts under identical circunistaiK^es of annealing, ikv. 
 While in Europe last autmnn, Dr. Chi(^hester Bell, of Univer- 
 sity College, London, suggested to nie that this inc<instancy of 
 result inight l»e due to chemii^al impurities in the selenium used. 
 Dr. Beli has since visited uiy laboratory in Washington, antl 
 has made a chemical examination of the various samples of se- 
 lenium I had colleirted from different parts of the world. As 
 I understand it to he his intention to publish the results of this 
 analysis very soon, I shall make no further mention of his in- 
 vestigation than to state that he has foun<l sulphur, ir«in, lead, 
 and arsenic in the so-(falled "selenium," with tra<tes of organiir 
 matter ; that a <piantitative examination has revealed the fact 
 tiiat sulphur constitutes nearly one per cent, of the whole mass; 
 and thai when these impurities are eliminated the selenium ap- 
 pears to be more (constant in its action and more sensitive to 
 light. 
 
 Prof. W. G. Adams* has shown that tellurium, like selenium, 
 has its electrical resistance aifected by light, and we have at- 
 tempted to utilize this snbstantic in place of selenium. The 
 arrangement of cell (shown in Fig. 7) was constru(;ted for this 
 purpose in the early part of 1880; but we failed at that time 
 to obtain any indications jf sensitiveness with a reflecting gal- 
 vanometer. We have since found, however, that when this 
 tellurium spiral is connected ii circuit with a galvanic; battery 
 and telephone, and exposed to tlie "''.tici of an intermittent 
 beam of sinilight, a distim^t nuisical tone is pi-oduced by the tele- 
 phone. The audible effect is much increased by placing the 
 tellnriuiti cell with the battery in the primary (drcuit of an in- 
 duction coil, and placing the telephone in the secondai-y circuit. 
 
 The enormously high resistance of selenium and the ex- 
 tremely low resistance of tellurium suggested the thought that 
 an allo^ of these two substanees might possess intei-mediate 
 electrical properties. We have accordingly mixed together 
 ♦Proo. Roy. Soc, vol. xxiv, p. 163. 
 
24 
 
 11 a. 
 
 Hcloiiiiiin iui«l tcUuritun in different jiroportidnH, and while we 
 do ni»t feel warninted ut the pi-e.-fent time in niiikiiiij detlnite 
 8tiiteiuent8 eonceriiing the resnltw, I nmy say that nywh rilloys 
 have proved to he sensitive to the aetion of light. 
 
 It (KHMirred to Mr. Tainter hefore my return to Washington 
 last Jamiary that the very great moleciUar distiirhance ))ro- 
 diiced in lamj)-l)la(!k hy the acttion of intermittent siiidight 
 should prodnee a corresponding distnrhaniie in an electrical cur- 
 rent pastied through it, in which ease lamp-Mack could he em- 
 ployed in place of selenium in an electrical receiver. This has 
 turneil out to he the case, and the importan(!e of the discrovery 
 is very great, especially when we consider the expense of su<^l' 
 rare suhstances as selenium and tellurium. 
 
 The form of lamphlack cell we have found most effec^tive is 
 shown in F^ig. 8. Silver is deposited upon a plate of glass, 
 and a zigzag line is then scratched through the tilm, as shown, 
 dividing the silver surface into two portions insulated from one 
 another, having the form of two comhs with interhw^king teeth. 
 
 Ea(!h comh is attached to a screw-eup, so that the cell (^an be 
 phuted in an electrical circuit when required. The surface is 
 then smoked until a giKHl tilm of lamp-black is obtained, filling 
 the interstices between the teeth of the silver combs. When 
 the lamp-black cell is connected with a telephone and galvanic 
 battery, and exposed to the influen<^e of an intermittent beam 
 of sunlight, a loud musicfal tone is produced by the telephone. 
 This result seems to be «liie rather to t!»e physical condition 
 I,han to the nature of the coiuUuiting material employed, as 
 metals in a spongy condition produce similar effects. For in- 
 stance, when an electrical current is passed through spongy 
 platinum while it is exposed to intermittent sunlight, a dis- 
 tinct musical tone is produced by a telephone in the anme (cir- 
 cuit. In all such cases the effect is increased by the use of an 
 induction coil; and the sensitive cells can be employed for the 
 reproduction of articulate speech as well as for the production 
 of musical sounds. 
 
 W^e have also found that loud sounds are produced from 
 lamp-black by passing through it an intermittent electrical 
 
\ while we 
 n^ (Ipfinite 
 such uHoys 
 
 V^UHhiri^foii 
 ItuiU'P })ro- 
 it siinliijht 
 fti'ical (Mir- 
 II 1(1 he em 
 This haw 
 ! (li8(!overy 
 ise of sikO' 
 
 effective h 
 ! of glass, 
 as slu>wn, 
 1 froin one 
 :iiig teeth, 
 ell van be 
 surfacie is 
 led, fillinijf 
 i. When 
 I galvanic 
 ;ent beam 
 elephone. 
 condition 
 »loyed, as 
 For in- 
 i spongy 
 ht, a dis- 
 same cii-- 
 ise of an 
 d for the 
 odiiction 
 
 ed from 
 ;lectrical 
 
f.-; 
 
8T 
 
 curroi.t ; and that it ran l.o uhimI an a tolcplionic rccpiver for 
 the reprodiicticMi ..f arti.-uhitc spwch by ('Iwtrifal iikmuis. 
 
 A (M.nvonicnt iikkIc ..f aiTaii«,'iii;,' a lainp-l.lack cfll for ox- 
 poriuuMitul purpoKCK is sliowu in Fi^. 5>. When an inti'rnntt.'nt 
 current in passed throuj,'h the lamp-Mark, (A,) or when an in- 
 termittent iKiani of Hiudit{ht falls upon it throuijh the fjlass 
 pkte B, a loud mtisieal tone (ran he heard hy applying,' the ear 
 to the hearing-tuhe C. When the li.^'ht and the electrical .-nr- 
 rentact sinndtaneously, two nnisical tones are perceived, \vlii<-h 
 produce heats when nearly of the same pitch. By prt.per ar- 
 rangements a c.inplete interference of sound can undoubtedly 
 be produced. 
 
 Upon the Meimvmttent of the Simoroiis h'ferts l^in^hmil l»J 
 J)lf event Snliddiieex. 
 
 We have observed that different substances produce sounds 
 „f very different intensities under similar (iircumstances of ex- 
 iMM-iment, and it has appeared to us that very vahudde informa- 
 tion n.ight be obtained if we could measure the audible effects 
 produce'il. For this purpose we have (-..nstructed several differ- 
 ent forms of apparatus for studying the effects, but as our re- 
 searc-hes ar'. not yet complete, I shall <-onHne myself to a sun- 
 pie description of m.me of the forms of apparatus we have tie- 
 vised. „ 
 
 When a beam of light is brought to a focus by means ot a 
 lens, the beam divergi.ig from the focal point becomes weaker 
 as the distance increases in a (calculable degree. Hence, if 
 we can determine the distances from the focal point at which 
 two different substances emit sounds of etjual intensity, we can 
 calculate their relative sonorous powers. 
 
 Preliminary experiments were made by Mr. Tainter during 
 my absence in Europe to a8(certain the distance from the focal 
 point of a lens at which the sound produced l)y a substance 
 became inaudible. A few of the results obtained will show 
 the enormous differences existing between different substances 
 in this respect. 
 
28 
 
 Dititnnve. fi'iHit tWnl l*i>'ni( i[t' hnn at irli'nh Simiiilx Ixcnini' 
 liudidlhle ii'liJi Dijf'irtnt SuhHtunnx. 
 
 Zinc <iiii|)liriii;iii, (polished) l.r>l in 
 
 Iliinl nililxT (liiiplini;;!!! !.!♦(» " 
 
 Till foil " 2.00 " 
 
 T»'l('|)li<iiic " (.lu|»iiiiu>(l iron) 2.15 " 
 
 Zinc " (inipolishcd) 2.15 " 
 
 White silk, (in rccciviT hIiowii in Ki^. 1.). . . . ;5.1() " 
 
 Whito woiKtHl, " " » u 4()i u 
 
 Yellow worsted, " 4» u u 4 o»', " 
 
 VeUow Hilk, " " " " +.l;{ " 
 
 White cottoii-wool, " » u u 4 38 u 
 
 (ireeii silk, " u u u 4 52 u 
 
 liliie worsted, " »i u u 4 ,5,) ,, 
 
 Tin-ple silk, " .* ^^ a 4^^^ " 
 
 l?rown silk, " i* '» "... 5.<>2 " 
 
 lilitck silk, " " " "... 5.21 " 
 
 Red silk, " " " " . . . . 5.24 " 
 
 IViaek worsted, " " " " ('..50 " 
 
 Jjiunp-Maek. In this (rase the limit of aiidiliilitv <'oiild 
 
 Mot he determined on aeconnt of want of space. 
 
 Sound perfectly an-lihle at a distance of 10.00 " 
 
 Mr. Taint<>r was convinced from these e.xju'riments that this 
 tiehl of resoach promised valiiahle results, and he at once de- 
 vised an apparatus for stuflyiii;^; the elYccts, which he de.scrihed 
 to me upon my return from Eurojx". Th; uppuiatus has since 
 heen constructed and i take great pleasure in showing it to you 
 ttt-day. 
 
 (1.) A heam of light is received hy twosimilar lenses, (A Ji, 
 Fig. 10,) which iiring tiie light to a focus on either side of 
 the interrupting tlisk (C) The two sidistanccs, whose sonorous 
 powers are to he <romj)ared, are ])lac('d in the recH'iving ves.sels 
 (I) P]) (so arrang(!d as to e.vpose e(jiial surfaces to the ac^tion 
 of the iieam) wiiich communic^ate l>y ile.xihle tuhes {V (i) of 
 etpial length, with the common hearing-tulic (II.) The re- 
 ceivers (I) E) are placed upon slides, which can he moved 
 along tlic graduated supports (I K.) The heams of light j.ass- 
 iiig through the interrupting disk ((J) are alternately cut off i>y 
 the swinging of a pendulmn, (L.) Thus a nmsicid tone is 
 prodjiced alternately from the suhstanee in D and from that 
 
Il/,S tlfllllllf 
 
 i.r.i III 
 
 l.!M» " 
 ti.dO " 
 2.15 " 
 2. in " 
 .'{.10 " 
 4.01 " 
 4.0»'. " 
 4.1H " 
 4.;{S " 
 4.52 '• 
 4.(!!» " 
 4. 82 " 
 5.(»2 " 
 5.21 " 
 5.24 " 
 (1.50 " 
 
 10.0(» " 
 
 s tlmt this 
 t oiU'e ilo- 
 <l('.><rnl>e(l 
 
 ' llH.>< KillCf 
 
 ; it toyoii 
 
 iOH, (A Ji, 
 
 r sido «»f 
 
 sonoi'on.s 
 
 "K vessels 
 
 lie sictioii 
 
 (F G) ,.f 
 
 The re- 
 
 e UK t veil 
 
 ,i;h( |iass- 
 
 II t off hy 
 
 tone is 
 
 oin that 
 
^ 
 
 81 
 
 ill K. (>ii('nl' tlic rtM'(>ivt>i-s JH ki^pf lit u ciiiiHtniit point iijM»n 
 itfi scale, and tlie (iflicr rwciver in moved towardH or from the 
 focMis of its Ik •im until tin- car decides tliat tlu' Konnds pro- 
 duced from Daiid K arc of c(|ual iiitciiHit}'. The relative po- 
 sitions (d" tlie receivers are then noted. 
 
 ("2.) Another metluMl of inveHti>;ation is lutHcd u|M>n the pro- 
 diicfion of an interference td sound, and the apparatus employed 
 \n shown in Fi^. II. The interrupter consists of a tuiiinj^- 
 fork, (A,) which is kept in continuous vihration hy meaiiH of 
 an eleetro-majjnet, ( H.) 
 
 A powerful heaiii of li^ht is lirought to a fo«Mis hetween tlu' 
 proiij^s of the tuniii;j-fork, (A,) and the passage (»f the heam is 
 more or less ohstriicted liy the vihration of tin: opaijiie Kcreeiis 
 ((/ I)) carried \>\ the prongs of the fork. 
 
 Ah the tiiinng-fork (A) produccH a Hound hy itH own vihra- 
 tion, it is j)laced at a sutlicient distanee away to he inaudihle 
 through the air, and a system of lenses is employed f(»r tint piir- 
 ])ose <d' hringing the undulating heam of light to the re<!eiving 
 leiis (E) with as little hms as possihle. The two receivers (F 
 G) are attached to slideH vhieli move upon the graduated sup- 
 p<»rtri (II I) on opposite sides of the axis of the Ixiain, and the 
 receivers are connected hy tlexihh' tuhes of unequal length (K 
 \j) communicating with the common hearing-tuhe (M.) 
 
 The length of the tulie (K) is such thai the koikh'ous vihra- 
 tioiiH from the receivers (F G) reach the common hearing-tuhe 
 (M) in opposite plii!><es. Under these cireumHtaiices silence is 
 produced when the vibrations in the receivers (F G) are of 
 ecpial intensity. Wluiii the intensities are unequal, a residual 
 effect itt perceived. In operating the instrument the position 
 of the receiver (G) remains (constant, and the reiteiver (F) is 
 moved t(» or from the focus of the heam until complete silence 
 is pntduced. The relative positions ()f the two receivers are 
 then noted. 
 
 (3.) Another mode is as fidlows; The loudness of a musical 
 tone produced hy the action of light is compared with the 
 loudness of a tone of similar pitch produ(!ed hy electrical 
 means. A rhettstat introduced into the circuit enables us to 
 
 
 
"""-'' iiSn'TiSgi 
 
 ■■I 
 
 32 
 
 inwisiiic til!' iinmunt of rcsistiiiuro required to render the elec- 
 triciil siMiiid e(|iiiil in intensity to the otlicr. 
 
 (4.) If thi; tuning-fork (A) in Fijjj. 1 1 ib thrown into vibra- 
 tion hy iin unduliitory insteud of an intennittent <Mirrent passed 
 throni^h tlie ekM'tro-niajjnet, (B,) it is proluihle that a niusica! 
 tone, eh'ctrieallv produceci in the receiver (F) Ity the aetion of 
 tlie same eurrent, wouhl he f(Mind <!apahle of extinfinishinj; the 
 effect produced in the reeeiver (G) hy tlie action of the nndu- 
 latory heani of li'jjht, in \vlii<-h case it should he possible to 
 establish an acoustic balance between the effects produced by 
 liijiit and electricity l»y introducing sufficient resistance into the 
 electric circruit.. 
 
 f^/)o,i //ir Nidxre of tin' Uiij^ f/tif Proilnce Siinoroiis Ejfectx 
 in I}[^\'i'eiit Siihstaih'Ci. 
 
 In my paper read l»efore the American Association last 
 August and in the present paper i liiive use " 'le word "light" 
 in its usual rather than its scientiffc sense, and [ have not hith- 
 erto attempted to discriminate the efi^ects produced i»y the dif- 
 ferent (tonstitnents of ordinary light, the tliermal, luminous, 
 and actinic rays. I find, however, that the adoption of the 
 word "pliotophone" by Mr. Tainter and myself has led to the 
 assumption that we believe<l the audil)le effects discovered by 
 us to be due entirely to the action of luminous rays. The 
 meaning we have uniformly attached to the words "photo- 
 pli(»ne" and "light" will be obvious from the following pas- 
 sage, (pioted from ni}' Boston paper: 
 
 " Although effects are produced as aitove shown by forms of 
 " radiant energy, which are invisible, we have named the appa- 
 " ratus for the produi^tion and reproduction of sound in this way 
 " the 'pliotophone' hern use (in oi'diminj beam of liykt contains 
 " tilt; /■Ki/.s irltirh ni'e oj>er(itit'ey 
 
 To avoid in future any inisunderstiindings upon this point we 
 have decided to adopt the term '■'■ /'ui/ioplionr,'" proposed by M. 
 Mcrcadier, as a general term siirnifying an apparatus for the 
 production of sound by any form of radiant energy, limfting 
 the words tlierniophone, photojyhone, and actinophone to appa- 
 
iider the, eleo- 
 
 111 into vil>rii- 
 
 iirrent pHssed 
 
 Hint a iinisicjil 
 
 file action of 
 
 ifj:nisliinj,' flip 
 
 '•f flio Mtldll- 
 
 >e jKtssihle to 
 
 i pnwlncod l»y 
 
 fiuice into the 
 
 iiirons KfevtK 
 
 sociution l^sf 
 word "hVlit" 
 iHve not liith- 
 ed I.J the dif- 
 ihI, InniinoHK, 
 iipfion of the 
 has led to the 
 diwiovered l»y 
 s i-Hjs. The 
 ords "photo- 
 (llowing pas- 
 
 1 l»y forms of 
 led the appa- 
 d in this way 
 Kjht contains 
 
 this point we 
 pose*! hy M. 
 •atUH for the 
 •gy, limiting 
 '/'t! to appa- 
 
 wA 
 
, i r 
 
 
 I li' 
 
 * I' 
 
 iif^j„it, 
 
i ''\ 
 
 ■■UMI 
 
 ^ 
 
 
 >S 
 
 i.^H— I 
 
 1 
 
 *«ii; 
 
3t 
 
 ratus for the production of sound l»y tluM'niiil, Inininous, or 
 iurtini(' ruyrt rewpectivcly. 
 
 M. M»'r<'u<li*'r, in the course of his reseureherf in riidiophonj, 
 purised an intermittent beam from an electric lamp through a 
 ()rism, and then e\aniine<l the audihle effectw produced in dif- 
 ferent parts of the spectrum. (( 'onijtfen /^em/tm, Dee. 6th, 1880.) 
 
 We have repeate<l this experiment, usinj^ the sun as (»ur source 
 of radiation, and have obtained results somewhat different from 
 those noted l»y M. Mercadier. 
 
 (1.) A l>eam of sunlight was retlec^ted from a heliostat (A, 
 Fig. 12) through an achromatic lens, (B,) so as t<» form an 
 image of the sun upon the slit (C.) 
 
 Th(! Iteam then })assed through another achromatic lens (D) 
 and through a hisidphide of carbon ])rism, (E,) forming a spec- 
 trum of great intensity, which, when focused upon a screen, 
 was found to l»e sutHiMently pure to show the principal absorp- 
 tion lines of the solar spectrum. 
 
 Tile disk-interrupter (F) was then turned with sutticient ra- 
 pidity to produce from live to six hundred interruptions of the 
 light per second, and the spe(;trum was explored with the re- 
 ceiver, (G,) which was so arranged that the lamp-black surface 
 expt)sed was limited by a slit, as shown. 
 
 Under these (arcumstances sounds were olttained in every 
 part of the visible spectrum, (excrepting the extreme half of the 
 violet,) as well iw in the ultrn-red. A continuous increase in 
 the htudness of the soimd was observed up<»n nutving the re- 
 ceiver (G) grr,dually from the violet into the ultra-red. The 
 point of maximnin sound lay very far out in the ultra-red. Be- 
 yond this point the sound Itegan to decrease, and then stopped 
 so su(!;lenly that a very slight motion of the receiver (G) made 
 all the difference l»etween almost nuiximum sound and (complete 
 silence.* 
 
 ('2.) The lamp-blacked wire gauze was then removed and the 
 interior of the receiver (G) was filled with red worsted. Upon 
 exploring the spcurtrnui as l»efore, entirely different results were 
 obtained. The nuixinuun effect was produced in the green at 
 
 * The resultH obtained in this uud subsequent experiments are shown in a 
 tabulated form iu Fig. 14. 
 
38 
 
 m\ 
 
 that j>!irt wluTc the red worstt'd iipju'ured to I>t' lilack. On 
 cither side of this pniiit the seuiid <;raduidly died away, heeoiii- 
 iii^f iiuuidihh^ on tlie one side in the middle of the indigo, and 
 on the other at a short distance outside the edj^e of the red. 
 
 (;i.) Upon 8nl»stitnting fjjrcen silk for red worsted the limits 
 of andition appeared to he the middle of the Itlue and a point 
 a short distancre ont in \ho ultra-red. Maxinnmi in the r<'d. 
 
 (4.) Some hard-ruhh(^r shavin<ifs were now placed in the re- 
 ceiver (G.) Th(! limits of iiudihilitv appeared t(» be on the one 
 han<l the junction of the fjjreen and hlue, and <tn the other the 
 outside edf^e(»f the nn]. Maxinntm in the yellow. Mr. Tainter 
 thou<i;ht he couhl hear a little way into the ultra-red, and to 
 his ear the inuximum was alxtut the junction of the red and 
 orange.* 
 
 (5.) A test-tuhe containing the vapor of sulphiu-ic ether was 
 then substituted for the recreiver (G.) Conmiencing at the 
 violet end, the test tube was gradually moved down the spec- 
 trum and out into the ultra-red without audible effec-t, but 
 when a certain point far out in the \dtra-red was reached a dis- 
 tinct musical tone suddenly made its appearantre, whicth disap- 
 peared as suddenly on moving the test-tube a very little 
 further on. 
 
 (6.) Upon exploring the spectrum with a test-tube contain- 
 ing the vapor of iodine the limits of audibility appeared to be 
 the middle of the red and the junction of the blue and indigo, 
 Maxinnnn in the green. 
 
 (7.) A test-tube containing peroxide of nitrogen was substi- 
 tuted for that containing iodine. Distinct sounds were ob- 
 tained in all part^ of the visible spectrum, but no sounds were 
 observed in the ultra- red. 
 
 The sounds were well marked in all parts of the violet, and 
 I even fancied that the audible effect extended a little way into 
 the nltra-violet, but of this I cannot be certain. Upon exam- 
 ining the absorption spectrum of peroxide of nitr<»gen it was at 
 once observed that the maximum sound was produced in that 
 part of the spectrum where the greatest nund)er of absorption 
 lines made their appearance. 
 
 * In the diagram Fig. 14 the mean of these readiugs is shown. 
 
luck. Oil 
 iiy, 1 »»•<'( nii- 
 i<li<r<>, iuid 
 lie red. 
 tiic limits 
 lid 11 point 
 tlio red. 
 in the tr- 
 im the one 
 other the 
 [r. Tainter 
 ;d, and to 
 e red and 
 
 ether was 
 ig at the 
 tiie spec- 
 iffect, hut 
 ihed a dis- 
 ich disap- 
 ery little 
 
 e contain- 
 red to he 
 id indigo. 
 
 as suhsti- 
 
 were oh- 
 
 iiids were 
 
 iolet, and 
 ! way into 
 on exam- 
 it wa.s at 
 3d in that 
 hsorption 
 
 wn. 
 
i; 
 
41 
 
 (8.) The fipoctriim wiis now oxplorod l»y a solftiium (;olI, unti 
 the utxlihlc effects were ohserved hy ineiiiiH of ti teh^plioiie in 
 tlie siinie •rtilvaiiic (rircuit with the cell. The niuxinnnn effect 
 was })r«Mhi<*etl in the re<l alKtut its junction with the orunjie. 
 The aiidiitle effect exten<le<l a litth> way into the ultra red on 
 the one hand and up as hi^h as the middle of the \ iolet on the 
 other. 
 
 Although the experiments so far made can only he consi<lered 
 as preliminary t<» (tthers of a more retinwl nature, I think we 
 are warranted in concludiu}^ that the ixttiire of the rtiyn that 
 produce sonorouH effects in (Hjfiiviit HnhstiiiireK depenih ujnm 
 th^ nature oj' the auhtttiitireti that ure e,vjh>ftetl to the tieiiin, (in<l 
 that tfie Hutiutln ure in every rune due to those ruytt of the t<j}ee- 
 truni that are ahsorU'd l>y the body. 
 
 The Hpectrophone. 
 
 Our experiments upon the ranj^je of audibility of different 
 Buhstanees in the spectrum have led us to the construction of a 
 new instrument for use in spectrum analysis, whicth was de- 
 scribed and exhibited to the Philosophit;al SiMiiety t»f Washing- 
 ton last Saturday.* The eye-piece of a spectrosc^ope is re- 
 moved, and sensitive substances are pla<tetl in the focal point of 
 the instrument Itehind an opaque diaphragm containing a slit. 
 These substances are put in connnunication with the ear by 
 means of a hearing-tube, and thus (he instrument is converte<l 
 into a veritable " spectrophone," lilce that shown in Fig. 13. 
 
 Suppose we smoke the interior of our spectrophonie receiver, 
 and fill the cavity with peroxide (d nitrogen gas. We have 
 then a combination that gives us good sounds in all parts of 
 the spectrum, (visible and invisible,) except the ultra violet. 
 Now, pass a rapidly-interrupted beam of light through some 
 substance whose ab8i>rption spectrum is to be investigated, and 
 bands of sound and silence are observed upon exploring the 
 spectrum, the silent posititMK-' corresponding to the absorption 
 bands. Of course, the ear camntt for one moment compete 
 with the eye in the examination of the visilde part of the spec- 
 
 ♦Proc. of Phil. 8oc. of Washingtou, April 10, 1881. 
 
42 
 
 J 1 
 
 tnun ; 1»ut in tin- iiiviHiMc part Im'voiuI the red, wlicri' tlu' cyo 
 iK iiHclcKH, tlu' I'jir is iiivulii;ii>lc. fii working in tliis rv^um itf 
 llif spfctrnni, liiinp-MiKk ulonc iniiv lie iist'd in tlic ripcctnt- 
 piinnic mu'ivor. Indcj-cl, tlic Honnd.-t pi-i.dii«r(>d l.y tliis sidi- 
 Htanco in tlio nltni-rcd nw. w» well nmrkod m to ••i.nHtitnt(^ (nir 
 inHtnnncnt .-i most rclialdc and convtMiicnf sniisfitiit*- fur tlu* 
 tlH-iino-pilc. A few ♦•xpcrinit-ntrt tliat have \n>i'u made may he 
 inten'sting. 
 
 (1.) The infernipte<l heaui was filtered through a saturated 
 solution of alum. 
 
 Result : Tlu^ ranjjfe ..f audihility in the idtra-red was slif,ditly 
 redueed hj the almorption of a narrow hand of the rays of lowest 
 refraiif^ihility. The sounds in the visihle part of the spectrum 
 seemed to he unaffected. 
 
 (2.) A thin sheet of hard ruhher was interposed in the path 
 of the heam. 
 
 Result : Well-marked sounds in every part of tlm ultra-red. 
 No sounds in the visihle part of (he spectrum, exct^pting the 
 t^vt^eme half of the red. 
 
 These experiments reveal the cause of the curious fact al- 
 luded to in my paper read l.efore the American Association 
 last August — that sounds were heard from selenium when the 
 l«»am was filtered through hoth hard ruhher and alum at the 
 same time. (See table of results in Fig. 14.) 
 
 (3.) A solution of ainmonia-sulphatc of copper was tried. 
 Result : When placed in the path of the heam the spectrum 
 disappeared, with the exception of the blue and violet end. To 
 the eye the spectrum was thus reduced to a single broad band 
 of blue-violet light. To the ear, however, the spectrum re- 
 vealed itself as two bands of sound with a broad space of silence 
 between. The invisible rays transnutted constituted a narrow 
 band just outside the red. 
 
 I think I have said enough to (ionvince you of the value of 
 this new method of examination, but I do not wish you to 
 understand that we look upon our i-esults as Ity any means 
 complete. It is often more interesting to observe the first tot- 
 terings of a child than to watch the firm tj-ead of a full- 
 grown man, and I feel that our first footsteps in this new field 
 
 ,^% 
 
 i:i 
 
*i'o tlio eye 
 region of 
 u' rtpcctro- 
 ' this 8ul»- 
 rttifntc^ our 
 tf for thd 
 kI(i iiiiiy lie 
 
 I Hutiiruted 
 ■)iH Hlif^litly 
 
 H of loWCHt 
 
 ? wpcrtniiu 
 
 II tl»' path 
 
 ! iiltni red. 
 'ptiiig the 
 
 18 fact nl- 
 
 LHKociution 
 
 when the 
 
 lint at tiie 
 
 3 tried, 
 spectrnm 
 tend. To 
 'oad hand 
 otrum re- 
 of silence 
 a narrow 
 
 value of 
 sh you to 
 ny means 
 5 first tot- 
 .f a full- 
 new field 
 
 i-i 
 
1 
 
 46 
 
 of w'.irnrc may have more of iiitrrcHt to ynii tlimr tlic fiilliT 
 i-i'kiiUh of matiin' rcHciircli. TIiIk iiniHt l»(^ my cxciiw for liavin^ 
 (Iwi'lt so loiij;' upon the «lctiiilH of iiicoin|>lft(> »'X|ifriiii('iitH. 
 
 I n'roj^iiizc till" fiict tliiit the HjHM'troplioiic iiniHt over n-miiiii 
 H inert' atljiinrt to the HjH'ctroHeojH', l»iit I aiiti(-i|>Ht(> that it h»K 
 II wiile mill in)h-]HMi(lent lieM of nKefiihieHs in thu iiivehti^^iitioii 
 of iilisorptioii Hpectni in the iiltni-red. 
 
 *i' 
 
 ^jj^jStiiiiMi MSmii il tmiTiU ii Mni iai l' i l ii'"' ' " ■ '"'' 1 'ii' i n i. u .i . M ll