70 Mr Ch. Martins on the Intensity of Sound 



In the case of electricity, however, there is no analogous 

 difficulty ; but we have instead the difficulty and expense of 

 developing current electricity by the chemical actions now 

 requisite. If carbon could be burnt or oxidized by the air, 

 directly or indirectly, so as to produce electricity instead of 

 heat, 1 lb. of it would go as far as 9-36 lb. of zinc in a Daniell's 

 battery, chiefly because there are as many atoms in 1 lb. of 

 carbon as in 5j lb. of zinc ; and partly because the affinity 

 (for oxygen) of each atom of incandescent carbon is greater 

 than that of an atom of cold zinc, minus the affinity of the 

 hydrogen for the oxygen in the water of the battery. Apart, 

 however, from such prospects of improved means of obtain- 

 ing electricity, its favourable feature, on the other hand, in 

 comparison with heat, is the reasonable expectation that 

 some form of apparatus may obtain from electricity a consi- 

 derable portion of the power which I have above determined 

 to be the dynamic equivalent of the electric current. 



On the Intensity of Sound in the Barified Air of High Moun- 

 tains. By Ch. Martins, D.M. & S. Communicated by 

 the Author. 



In nature, where the artificial conditions of the laboratory 

 are wanting, the most simple experiments in physics, and 

 apparently the most conclusive, are found complicated with 

 new elements and unforeseen difficulties which change or 

 modify the conclusions which we are tempted to deduce from 

 them. The following results are a striking proof of the 

 truth of this statement ; and I may express the hope that 

 they will draw the attention of physicists to the still unknown 

 causes which produce a variation of the intensity of sound in 

 the open air. 



So early as 1706, Hauksbee demonstrated, by experiments 

 made in the fields, that the sound of a bell, under a receiver, 

 is so much the stronger as the air is denser, and that it be- 

 comes weaker in proportion as the air is rarified.* Until 



* An account of an experiment made at a meeting of the Royal Society of 

 Gresham College, upon the propagation of sound in condensed air, together 



