Van Mons. 233 



storms might be prevented over a whole kingdom by an exten- 

 sive series of conductors : but it will, I presume, appear unques- 

 tionable, that neither of these proposals cm i; Iiave proceeded from 

 a sufiiciently attentive consideration of the subject, and there is 

 reason to think thev would never have been advanced by any one 

 practically conversant with the details of such phenomena. 



There are two modes in which a conducting rod .nay be sup- 

 posed to influence the electricity of the atmosphere. 1st, It 

 mav be conceived to diminish the usual positive electricity of 

 the air. And 2ndly, it may be regarded as a source of constant 

 diffusion, a kind of silent discliarger, calculated to prevent the 

 formation of regular thunder clouds, by transmitting the electri- 

 citv of tlieir elementary modifications to the earth. If the first 

 mode of operation were admitted as probable, it would teach us 

 nothing ; for at present we know not either the origin or pur- 

 poses of this regular electricitv, nor the absolute relation it bears 

 to those changes in the state of atmospherical moisture and dry- 

 ness bv which its indications are so obviously and materiallv af- 

 fected : still less can we pretetid to assert that it is, or is not, es- 

 sential to vegetation. Besides, if a conducting-rod had the 

 power here supposed, how materially would the usual electricity 

 of the atmosphere be diminished bv natural causes ! for the sur- 

 face of the earth abounds with points and prominences, of ecjual 

 efficacv as silent dischargers ; and every tree, every spire, and 

 each mountain and promontory, must be then regarded as sub- 

 tracting constantly irom the electricity of the atmosphere : it is 

 indeed probable they do so, at least occasionally ; but the (pian- 

 tity thus distributed bears so small a proportion to the uiiole, 

 that the usual .signs exhibited by our instruments are neai iv as 

 powerful in the neigh'Dourhood of an extensive conductor, or a 

 lofty tree, as in the open air ; and the horizontal e.^tension of a 

 mile and a quarter of wire uninsulated, and at the elevation of 

 100 feet from the ground, has been found to have but a very 

 trifling effect on the atmospherical electricity in its viciiiiiv*. 

 It may also be observed, that the moditication of cloud . .'led 

 stratus remains positively electrified, thi.ngh its lower surfai.e is 

 in contact with the earth. 



Thes oi)jections apply with still greater mrce to tiie second 

 idea ; for thunder clouds are usually formed at such an eleva ion 

 from the earth's surface as to be entirely out of the influence of 

 the lii.^hest projections thereon ; and when thev descend within 

 the striking distance, we know from tlie iicnnencv of daniUge 

 in large towns, where there are numerous conductors, besides 



• I'liis cxjicrimcnt was made by that very active electriciun, A. Crosse, 

 E«q. of liroomficld. 



