430 Prof. A. M. Mayer's Researches in Acoustics, 



intensity, was obtained with a sheet of cold carbonic acid 

 gas ; while cold dry hydrogen closed the mouth of the resonator 

 more effectively than either of the above gases, but was far in- 

 ferior in this shielding action to the sheet of heated gases above 

 the bat's-wing gas-flame. "We should not place too much confi- 

 dence in measures of the reflecting-power of surfaces made by 

 the method just described, and which I have used merely to 

 give approximations of the reflecting-powers of the above named 

 gaseous sheets ; for the substance which closes the mouth of the 

 resonator may allow a considerable portion of the sonorous 

 vibrations to enter the latter, and yet the resonator may not be 

 able to reinforce the sound by reason of its being thus thrown 

 out of tune with the fork by an unyielding surface closing its 

 aperture. Thus, a sheet of thick note-paper prevents resonance 

 as effectively as a thick piece of Bristol-board, or a plate of 

 metal; yet we know well that these substances have very different 

 powers to reflect sonorous vibrations. As a flat coal-gas flame 

 equals a piece of tracing-paper in deflecting sonorous vibrations, 

 it follows that we can substitute the former for the latter in all 

 experiments where the presence of the paper produces, by its 

 reflecting-power, an alteration in intensity or in pitch. Thus, 

 if we vibrate a fork before the mouth of a resonator while the 

 nipple of the latter is open, we obtain a far inferior reinforcement 

 to what takes place when the nipple is closed. Now the nipple 

 can be partly closed with a gas-flame or a sheet of heated air. 

 Thus, alternately closing and opening the nipple of an Ut 4 reso- 

 nator with the flame of a Bunsen burner, gives excellent re- 

 sults*. The reflecting-power of a bat's-wing flame is also well 

 shown by successively closing and opening the mouth of any 

 resonant box of forks in the octave Ut 4 to Ut 5 . Also, if the 

 plug be taken out of the ends of closed organ-pipes and these 

 pipes be placed horizontally, the reflecting effect of the flame is 

 heard when the latter is passed forward and backward across 

 the open ends of the pipes while the ear is placed in the axes of 

 the pipes. The simplest method, however, is to sound the fork 

 (either continuously by electro-magnetism, or by a bow) in front 

 of its resonator, and successively to close and open the mouth of 

 the latter with a flame or sheets of heated gas, or of cold vapours 

 or gases. The contemplation of these experiments naturally calls 

 up the question, Is the action of the flame due entirely to reflec- 

 tion ? may it not also absorb part of the sonorous vibrations, as 

 in the analogous phenomena of the reflection of light ? If the 

 intensity of the sonorous vibrations which have traversed the 



* In all of the experiments described in this paper care was taken that no 

 heated air or gases entered the resonators and thereby put them ont of 

 tune. 



