538 TRANSACTIONS OP THE AMERICAN INSTITUTE. 



range of Imman vision, are only known to us by the wonderful effects they 

 produce in the hands of the skillful photographer. 



This paper will be devoted to that subdivision of Clydonics which includes 

 considerations regarding- the relative action of the most common media of 

 liglit and sound. 



It is very difficult, if not impossible, to form a correct conception of the 

 extreme attenuation and rapid motion of the ethereal medium which is 

 termed peth, to distinguish it from the ether of chemistry. In papers pre- 

 viously presented I have endeavored to show that all the distinct and appa- 

 rently diverse effects known as heat, light and actinism may be the result of 

 wave motions of the same fluid varying in velocity. Bearing in mind the broad 

 distinction between the normal movements of air waves and the transverse 

 movements of a^th waves, let us by gradual ascent upon the atmospheric 

 ladder, so to speak, reach the dizzy height at which rapidity of motion is appa- 

 rently the rule, and rest the exception, in the wonderful economy of nature. 



The propagating o!' sound through air, having the temperature of the 

 melting point of ice, the mercury f the barometer standing at 30 inches, 

 is about''l,090 feet per second. Its velocity is directly as the square root 

 of the elasticity and inversely as the square root of the density of the air. 

 When the temperature is increased one degree on the Fahrenheit scale, any 

 gas is increased 4', in bulk. The form ila of Newton, with the correction 

 of Laplace, expressing the ratio of the specific heat of air at a constant 

 volume, with its specific heat at a constant pressure, has been confirmed 

 by actual measurements. In gases under the same pressure and of the 

 same temperature, the velocity of sound is inversely as the square root of 

 their densities. D along produced tones from organ pipes by means of dif- 

 ferent gases, and found that sound was propagated in one second through 

 hydrogen 4,154 feet, through carbonic oxide 1,105 feet, through air 1,093 

 feet, through oxygen 1,040 feet, through carbonic acid 857 feet. The 

 density of oxygen being 16 times that of hydrogen, it will be seen that 

 the velocity of sound thus obtained id these gases correspond very nearly 

 with the calculated rate. 



The elasticity of the atmosphere being directly as its pressure, the 

 velocity of sound would be the same at all heights through air of the same 

 temperature. The variations caused by decrease of heat in upward pro- 

 gress can be calculated from data gathered by Mr. Glaisher during balloon 

 ascensions to the height of five miles. Without attempting to give even 

 a near approximation towards the true height of the atmosphere, which 

 must have a definite boundary at that line wliere gravitation exactly coun- 

 terbalances the repulsive force of its particles, attention is called to the 

 following table showing its rarefaction; increasing in geometrical ratio 

 with each ascent of 3.4 miles. 



At 17 miles it is 32 times rarer. 



