64 



Mr. Harvey on the Formation of Mists. 



It may also be added, that the temperature of the air is 

 sometimes considerably less than that of water, during rain. 

 The following are instances : 



The example of the 31st of July, exhibits a remarkable dif- 

 ference in the temperatures of the air and water. 



Art. VIII. On the Light produced by the Discharge of 

 an Air-gun: 



To the Editor of the Quarterly Journal of Science and the Arts. 



Sir, 



Among the various methods of producing light, taken notice 

 of by philosophical writers, that from the discharge of the air- 

 gun has not escaped observation. It is asserted that a flash 

 of light is seen at the muzzle of the air-gun, when it is dis- 

 charged in the dark. This light is supposed to be electric, 

 and to be produced by the sudden expansion of the condensed 

 air in the atmosphere. Having often attempted to produce 

 light in this manner without success, I varied the experiment 

 by introducing successively warm, dry, and damp air ; and 

 discharging them in moist, dry, frosty and warm atmospheres ; 

 but always without succeeding in the production of light. Lest 

 the barrel of the gun might be supposed to absorb the electric 

 fire, I discharged the spherical magazine itself by striking 

 with a hammer on the valve, but still without the expected 

 success. 



One evening last autumn, while discharging the same gun, 

 during twilight in a back court, I observed for the first time a 

 faint light. I now concluded that it must be from the wadding 

 exciting friction on the inside of the barrel (all the former 

 experiments having been made with an unloaded gun). But, as 



