ON THE ELECTRIC COLUMN* Q55 



pirecipilatlon ceases, extreme moisture still subsists in the 



air; as Mr. de Saussure and myself have found »n all our 



hygroscopical experiments. Now, I have said above from 



observations on hio;h mountains, that air is there dry till the 



moment before the formation of clouds, and that as soon as 



the thuds are dissipated, the hygrometer indicates the same 



dryness as before. This evidently shows, that the produc- Clouds ami 



./,,, , .1 ,i- •,! Tain from Ue- 



tion ot clouds and ram have their cause in the very stratum c, mpositionof 



of a«' where they are manifested ; and this cause cannot be the air. 

 any other than a decomposition of the air itself. 



Lastly, in these very clouds, which, being themselves a Thunder »nd 

 conducting mass, lean besides against mountains, it happens '* 

 sometimes that lightning and thunder are produced; and 

 this, as I have said before, without any previous sign of an 

 uncommon quantity of electric Jluid in them. This also 

 points out some operation taking place in these clouds, by- 

 some modification in the cause which commonly produces 

 a simple rain. The electric jiuid, thus suddenly disengaged, 

 must have been before in some chemical combination in the 

 nir itself, which prevented its manifestation, and is then 

 destroyed. When we are above the clouds, we niay see (as 

 it has happened to me) lightning darting upwards, as it is 

 commonly seen darting downwards when we are under the 

 clouds; and even in this last case, we may judge that light' 

 ning is darted upwards, when we see only a great sudden 

 Vight in clouds, without any Jiashi followed however by 

 thunder. 



The above are leading facts in the maze of atmospheric These Ejcis 



, .,.,.. , . ^ . , evince the ex« 



phenomena, certainly indicating the existence, in the at- istence of sub« 



mosphere, oi subtile fiuids, beside those which have hitherto tile fluids i:i 



been discovered. This is the general object, which I am phgre. 



going to examine. 



I shall here begin by explaining one of the results of my Investigatioa 



long labours in the pursuit of the measurement of heights by ^' "^"^""ea- 

 " ' . . surenjent of 



the tarowcfcr, of which all the steps are described in my heights by tk^ 

 woik Recherches sur les Modifications de V /Itniosphhe, pub- barameter. 

 lished in 1772. My experiments and observations were first 

 directed toward these two points. J. To obtain, by a great 

 number of observations at different measured heights, on 

 mountains and towers, a coefficient expressive of height, to 



the 



