284* SPEAKING TRUMPETS. 



attention was direaed to having a hard, elaftlc and thin fub- 



ftance, that it might vibrate in unifon with all the tones, and 



refledl the fonorous rays which ftruck it in all diredions. 



L»rabert*s In 1763, Lambert withdrew from the theory of fpeaklng 



vSon injurc«*'""^P®*^' *^® vibration of the materials of which they are com- 



the articulation pofed: he (liowed that the vibration of the fides which is cal- 



of the founds, ^ulated to augment the intenfity of a long continued found, 



would render articulate founds confufed, which muft fucceed 



each other rapidly ; that in this cafe therefore it would be ne- 



cetTary to fpeak extremely flo'w, and that, even by fpeaking 



flowly, it would be impoffible to diftlnguifti the confonants, 



which are only momentary modifications of the vowels; that 



the latter, pronounced in the trumpet, would be fo fonorous, 



that the confonants muft be guefied at, which would be ex- 



Speaklng trum- tremely difficult. By fprinkling the exterior furface of a tin 



but\te''founa'is O^eaking-trumpet with faw-duft, I fatisfied myfelf that the 



equally ftrong furface vibrated in fome circumfiances, but I was equally fa- 



when thcvibra- tisfied, on covering the outfide of the trumpet with a foft loofe 



iluff to ftop and obftrudl its vibrations, that the intenfity of 



the found was no lefs ftrong, in this fecond cafe, and, that 



thus the vibration of the fubftance of the trumpet was, at feaft, 



ufelefs, if it was not injurious to the diftinclnefs of articulated 



founds. 



In his memoir, publiflied among thofe of the Academy of 

 Berlin, for the year 1763, Lambert has attributed all the aug- 

 mentation of the intenfity which the found experiences by 

 fpeaking into a trumpet, to the refle61ion of the fonorous rays 

 on the fmooth and poiiftied furface of the interior of this inftru- 

 ment; he fays that, of all the forms, that beft calculated to 

 concentrate the found by retleding it, and the moft eafy to 

 Proportions of aeon ftrud, is the conic form: he afterwards ftiows that the 

 conical fpeaking j^f^y^^^ \^ ftrengthened in conical fpeaking trumpets, in the pro- 

 portion of double the length of the cone which forms the trum- 

 pet to double the fize of half the angle at the fummit of the 

 cone, fuppofi ng the length of the cone to be equal to the ra- 

 dius. If the angle of the cone is made = <p, the found is 

 ftrengthened in the proportion ^2 : 2 (fin. l^). 



Seeking, from thefe formulae, to difcover what would be 

 the beft proportions to give to conical fpeaking trumpets, he 

 found that whatever the angle of the fummit of the cone was, 

 ks bafe muft be equal to the diftance between the fummit of 



- the 



