TRUMPET. 



canal, whofe aperture is not above one-fourth of an inch in 

 diameter, which is applied to the car. Thefe tubes are 

 often bent in a manner fomewhat refembling the letter C, 

 except that in general the fmall end is bent much lefs than 

 the other. The conftruftion of thefe inftruments evidently 

 ftiev/s how they contribute to affilt the hearing ; for the 

 weak and languid pulfes of the air being received by the 

 large end of the tube, and reflefted feveral times from its 

 fides in pafling to the fmall end, are condenfed, and entering 

 the ear in this condenfed ftate, ftrike the tympanum with a 

 greater force than they could have done without the inter- 

 vention of the tube : the found is louder, but lefs diftinft. 

 Hence it appears, that a fpeaking-trumpet may be applied 

 to the purpofe of a hearing-trumpet, by turning the wide 

 end towards the found, and putting the ear to the narrow 

 end. 



Trumpet, Speaking, is a tube from fix to fifteen feet 

 long, made of copper or of tinned iron-plates, perfeftly 

 ftraight, and with a very large aperture ; the mouth-piece 

 being big enough to receive both lips. The edge of the 

 narrow end is generally covered with leather or cloth, in 

 order that it may more effeftually prevent the pafTage of any 

 air between the trumpet and the face of the Ipeaker. 



The mouth being applied to it, carries the voice to a very 

 great diftance, fo that it may be heard diftinftly a mile, or 

 more ; hence its ufe at fea. A perfon who is not in the 

 direftion of the trumpet will hear the found of it both 

 weaker and lefs diftinft, in proportion as he is more or lefs 

 diftant from the direftion of the found ; which is the direc- 

 tion llraight before the trumpet. 



The words which are fpoken through a fpeaking-trumpet 

 may be heard much farther and louder, but not fo dillinftly, 

 as without the trumpet. 



A fpeaking-trumpet has alfo been applied to the mouth 

 of a gun or piftol, by which means the explofion has been' 

 rendered audible at a vaft dillance. Such contrivances may 

 be ufed as fignals in certain cafes. 



The invention of this trumpet is held to be modern, and 

 is commonly afcribed to fir Samuel Moreland, who called it 

 the tuba Stentorophomca. 



Of this inftrument an account was publifhed at London 

 in 167 1, in 3 work entitled " Tuba Stentoro-phonica," in 

 which the author relates feveral experiments made by him 

 with this inftrument ; the refult of which was, that a 

 fpeaking-trumpet conllrufted by him, five feet fix inches 

 long, twenty-one inches diameter at the greater end, and 

 two inches at the fmaller, being tried at Deal caftle, was 

 heard at the diftance of three miles, the wind blowing from 

 the (hore. 



But Ath. Kircher feems to have a better title to the in- 

 vention ; for it is certain he had fuch an inftrument before 

 ever fir S. Moreland thought of his. 



Kircher, in liis " Phonurgia Nova," publifhed in 1673, 

 fays, that the tromba, publifhed laft year in England, he 

 invented twenty-four years before, and publifhed in his 

 Mufurgia : he adds, that Jac. Albanus Ghibbifius, and Fr. 

 Efchinardus, afcribe it to him ; and that G. Scottus teftifies 

 of him, that he had fuch an inftrument in his chamber in the 

 Roman college, with which he could call to, and receive 

 anfwers from the porter. 



Indeed, confidering how famed Alexander the Great's 

 tube was, with which he ufed to fpeak to his army, and 

 which might be diftinftly heard a hundred ftadia or fur- 

 longs, it is fomewhat ftrange the moderns fhould pretend 

 to the invention ; the Stentorophonic horn, or tube of Alex- 

 ander, of which there is a figure preferved in the Vatican, 

 10 



being almoll the fame with that now in ufe. See StenTo* 



ROPHONIC. 



The principle upon which this inftrument is conftrufted is j 

 obvious ; for as found is ftronger in proportion to the denfitj 

 of the air, it muft follow, that the voice pafling through 

 tube or trumpet, muft be greatly augmented by the conftant"* 

 refledlion and agitation of the air through the length of the 

 tube, by which it is condenfed, and its aftion on the ex- • 

 ternal air greatly increafed at its exit from the tube. 



In a fpeaking-trumpet, the found in one direftion is fup- 

 pofed to be increafed, not fo much by its being prevented 

 to fpread all round, as by the refledlion from the fides of 

 the trumpet. But as the real aftion of the inftrument, or 

 the true motion of the air through it, is not clearly under- 

 ftood ; different perfons, according to their particular con- 

 ceptions of the cafe, have recommended peculiar fliapes for 

 the conftruftion of fuch trumpets : fome having recom- 

 mended a conical fhape, others that which is formed by the 

 rotation of certain curves round their axes ; others, again, 

 have recommended an enlargement or two of the cavity in 

 the length of the trumpet, &c. That which has been 

 more commonly recommended as the befl figure for fuch 

 trumpets, is generated by the rotation of a parabola about 

 a line parallel to the axis. 



In order to eftimate the efFeft of this inftrument, let us fup- 

 pofe A B (P/rt^f XXI V. MifceUany,fg. 7.) to be fuch a length 

 of tube as admits one refleftion of the found, emitted by the 

 fpeaker, from the fide B B ; let AP be another length, in 

 which the found or voice is reflefted five times by the fides, 

 in%. in B, C, D, E, and F : the found ftriking the metal 

 tube in B is the fame as that at F ; but the number of parts 

 forming tke periphery of the circle in B is to that in F, as 

 the diameter B B is to the diameter F F ; and therefore the 

 intcnfities with which the parts of the metal will be moved 

 in thefe peripheries, will be in the inverfe ratio of the peri- 

 pheries, or of the diameters B B, F F. But the parts of 

 the metal move the air contained within the peripheries of 

 the circle, or conftituting tlieir refpeftive areas, which are 

 as the fquares of the diameters : i. e. the air agitated in B 

 is to that agitated in F, as B B ' to F F^ ; and confequently, 

 the intenfity of the fame found in the tube of the length 

 A B, is to that in tiie length A F, as B B ' to F F ', and 

 the inverfe ratio of the diameter B to F : or, the intenfity 

 in A B is to that in A F :: F F y. B B^ : B B x YY\l.e. 

 dividing the laft ratio by B B X F F :: BB : F F. But the 

 intenfity of the found increafes the more frequently it is re- 

 flefted from the fides : let then the number of refieftions of 

 the found in B be n, in F it will be 5 «, and therefore the 

 whole intenfity of the found in B is to that in F as /; x B B 

 to 5 n X F F. Confequently, the longer the tube the more 

 numerous will be the refieftions, and the greater will be the 

 increafe of the found, and the farther may it be heard. 



A man, fpeaking through a tube four feet in length, may 

 be underftood at the diftance of 500 geometrical paces • 

 with a tube of i6- feet, at the diftance of 1800 paces ; and 

 with a tube 24 feet long, at a greater diftance than 2500 

 geometrical paces. 



The found will be alfo heightened by having the remoter 

 aperture of the tube vi'ide, more than if it were narrow. 

 However, the efFeft of the tube in magnifying found, either 

 for fpeaking or hearing, depends principally upon its length : 

 neverthelefs fome advantage may be derived from its parti- 

 cular form and fhape. 



Some have propofed the figure which is made by the re- 

 volution of a parabola about its axis, as the beft ; where 

 the mouth-pieee is placed in the focus of the parabola, and 



confe- 



