1 62 Mr. W. R. Birt on the connexion of Atmospheric Electricity 



this fluid; and I conjecture that pure air and electricity are 

 actually incapable of uniting; and therefore it is that air is 

 never known to attract, absorb, nor conduct electricity, but in 

 proportion to the conducting substances with which it happens 

 to be occasionally mixed: nor is air excitable of electricity by 

 any means that is yet known ; therefore air does not appear 

 to be either an electric or a conducting body. 



" It is in consequence of these peculiar properties of air 

 that it is found to insulate the electric fluid more perfectly 

 than any other substance." 



In the above extract we are informed of the perfect indij- 

 ference of air to electricity, whether we regard the latter as a 

 fluid, or adopt the more modern view of its being a force 

 brought into play by heat, friction, &c. Keeping steadily in 

 mind this perfect indifference, the following extract presents 

 us with a mode by which the electricity, or regarding it at 

 present as a force, *' the electric force," is conveyed from one 

 portion of the atmosphere to another : — 



" The electricity rises invisibly from the earth concealed in 

 the aqueous vapour ; and as the vapour ascends higher and 

 higher into cooler air, it becomes more condensed, by which 

 the electricity which it contains will become more condensed 

 also*, insomuch that it will now display its energy; and in 

 whatever direction it moves, it is sure to move actively, ani- 

 mated with a penetrating and expansive force ; for in this state 

 proper instruments will easily accumulate and detain it, so as 

 to render it visible." 



In this paragraph Read says " the electricity rises invisibly 

 from the earth concealed in the aqueous vapour;" in other 

 words, each particle of vapour as it rises from the earth is 

 electrified (from what source we do not now stop to inquire), 

 or is capable, when placed in a proper situation, of exhibiting 

 that force which we are in the habit of terming " electric." 

 It may be well here to contemplate each particle of vapour as 

 surrounded by pure air, through which, as air, the electric 

 force will not pass, /. e. the force cannot be communicated 

 through it unless it is of sufficient tension to " strike " through 

 the space to another conducting body. Now if by any means 

 heat is abstracted froui the vapour particles, or they pass into 

 a stratum of cold air, they become condensed, i. e. they are 

 reduced in size, contemplating each individual drop, or several 

 run together and produce visible vapour ; in both cases the 



* It is well known that if equal quantities of electricity be imparted to 

 two unequal insulated conductors, the electricity on the least sur/ace will 

 become more intense than on the largest. Electrified vapour is also sub- 

 ject to this law. [J. Read.] 



