SPEAKING TRUMPETS. 285 



the cone and the mouth of it, and that its length muft be equal 

 <o the diameter of the mouth, divided by four times the fquare 

 of the fine of half the angle of the cone : that thus in a trum- 

 pet of fix feet in length, the angle of the conemufl be 16** 17. 

 and that fuch a fpeaking-trumpet would make the found 96 

 times more intenfe. 



Lambert therefore, as well as thofe who have preceded hira, 

 confidered the augmentation of the intenfity of the found in 

 fpeaking trumpets, as the refult of the adion of the refle<5lion 

 of the fonorous rays againftlhe interior fides of tlieinftrument. 



It would appear that fince Lambert's memoir, fpeaking Thefe Inftni- 



trumpets have been made ufe of, without attending to the J^rr^beerdnl 



^ caufes which augment the intenfity of the found, and, in fad, ftrufted without 



it is feen that in all works in which this inftrument is fpoken of, attending to the 



cjufes ol^ the 

 its effeds are attributed either to reflection alone, or to reflec- jncreafe of 



tion combined with the vibration of the fubftance of which it found. 



is formed. 



If we compare the theory of fpeaking trumpets with that of J^^o^'yoffpeak- 

 the inftruments which have fome refemblance to it, fuch as ^ther inftru! ''" 

 trumpets and hunting horns, we muft be attonithed to find thatmcnts. 

 they are referred to different principles. In the fpeaking trum- 

 pet, the caufe is attributed to the refledion of the found; in 

 the other inftruments to the vibration of the air contained in the 

 tube. Why thefe tvyo caufes, while the efFedsare analogous? 

 This analogy has led me to inquire if, in reality, the refledion Does refleftion 

 produced the augmentation of the intenfity of articulation in Jf"" ^'"« 

 horns and acouftic tubes, as well as in fpeaking-trumpets, as is found ? 

 generally believed. 



On examining the ears of animals, it is feen that the great- Animals do not 



eft number have an exterior auricle, which moft of them di- ^^^L^^ ^^^ '^'^' 



flection of 

 red towards tl^e place from which the found proceeds; this found. 



auricle being, in many animals, covered inwardly with hair, 



• which flops and hinders the refledion of the found, it is rea- 



fonable to conclude that it is not by refledion that the found is 



tranfmitted into the ear. 



When afterwards we obferve the form given to acouftic horns. Ear- trumpets 



which is that of a cone, the fummit of which, flightly tf un- ^°^"°JJ^'^"j[- 



cated, is placed in the ear, we are quickly led to conclude that reflexion. 



the found is not tranfmitted by refledion ; for the angle of the 



incident ray being increafed at each refledion by that of the 



«one, aft,er a number of determinate reftedions, the angle 



would' 



