Effect of the Motion of the Air within an Auditorium. Ill 



trie potential by contact of dissimilar substances is attributed 

 to the nature of the gas or atmosphere surrounding them. It 

 is probably so only in so far as such gas produces, by conden- 

 sation, a film of itself on the surfaces of the substances in 

 question. 



In experiments where the difference of potential of a metal 

 and a liquid in contact is the subject of investigation, the 

 arrangement is probably analogous to a two-fluid cell with 

 plates of the same kind of metal, i. e. the metal under exami- 

 nation — one of the fluids in the supposed cell being that in 

 contact with the metal, and the other being the film of mois- 

 ture &c. condensed on the metal. 



Slight variations in the nature of this film, due perhaps to 

 the remains of whatever may have been used for cleaning the 

 metal, or to such vapours as might be present in the atmo- 

 sphere of the laboratory, would produce corresponding varia- 

 tions in the amount of difference of potential observed — just 

 as a small quantity of hydrogen-sulphide in the atmosphere 

 surrounding the copper and iron in contact reverses the rela- 

 tive potentials of these metals. This would no doubt account, 

 at least partially, for the discrepancies in the results obtained 

 by different observers, and indeed by the same observer in 

 different experiments with the same liquid and metal. 

 Belfast, December 1878. 



XYI. Effect of the Motion of the Air within an Auditorium 

 upon its Acoustic Qualities. By W. W. Jacques*. 



IT is the purpose of this paper to give an account of some 

 experiments made for the purpose of determining the 

 effects of the currents of air within an auditorium upon its 

 acoustic qualities. These experiments are in three series: — ■ 

 the first being a laboratory investigation into the effects of 

 currents of air upon a ray of sound ; the second and third, 

 studies, by different methods, of the effects of the currents of 

 air in a lecture-hall and a theatre, upon the waves of sound. 



Since the air of a hall is the medium by which sound is con- 

 veyed from the speaker or singer to the hearer, it would cer- 

 tainly seem of fundamental importance that this air should be 

 in the condition best suited to the propagation of sound. 

 Experiments made by the author, in a considerable number of 

 halls, show that the atmosphere is almost invariably disturbed 

 by currents of air of varying density crossing the room in all 

 directions. These currents have been traced out with thistle 



* A reprint from the Journal of the Franklin Institute, December 1878, 

 communicated by the Author. 



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