392 On the Dust-storms of India. [No. 5, 



30° , take it out, wipe it dry, hold it up to the light, and observe the 

 bright spot, and continue to wipe off the dew so long as it is deposited 

 and dulls the bulb : at the instant it clears off mark the temperature. 

 This I have compared frequently with DanielPs hygrometer, cooled by 

 means of chloroform, and find them both correspond with the greatest 

 accuracy. 



This is a digression ; but I have no time to arrange, and must there- 

 fore put down my remarks as they occur to me. 



The dew-point varies very much, but is usually many degrees below 

 the temperature of the air, 20° to 50° or more. 



It also varies according to the time of year. During November last 

 the mean temperature of the dew-point was about 47° , that of the air 

 about 71° . 



In January 1850, dew-point 43°; in the air, 61°; and the mean 

 temperature of self-registering thermometer 45°-4. 



In February 1850, mean of dew-point 48°, and air 64°-5. 



April 1850, mean temperature of dew-point so far, is about 60°, and 

 the air 84° . 



The sparks, or the stream of electricity, as it is seen passing from 

 one wire to the other, is in some cases, and during high tension, 

 doubled or trebled ; and is never straight, but invariably more or less 

 crooked. 



Various kinds of sparks are seen ; at times one end of the wire has a 

 star ; and from the wire, when held just beyond striking distance, a 

 brush is seen curved, which, when viewed through a lens, seems com- 

 posed of a stream or curved brush of bright globules, like a shower of 

 mercury. 



The manner in which the electricity acts upon the dust and light 

 bodies it meets with in its passage, is simple enough. I suppose the 

 particles similarly electrified and mutually repulsive, and then, together 

 with the whirling motion communicated to them, are whisked into the 

 air. The same takes place when the electricity moves over water. 

 The surface of the water becomes exposed to the electric agency ; and 

 its particles, rendered mutually repulsive, are in the same way whirled 

 into the air. 



At sea the waterspout is thus formed. First of all is seen the cloud 

 descending, and beneath may be observed the water in a cone, misty 



