si 
and of the Baltic Sea in particular . 
important documents for this purpose, and similar ones should 
be begun to be collected in other countries *. 
Art. XIV. — On certain Circumstances connected with the Con- 
densation of Atmospheric Humidity on solid surfaces. By 
Henry Home Blackadder, Esq., Surgeon. Communicated 
by the Author. 
The condensation of aqueous vapour from the atmosphere 
on the surfaces of solid bodies, is one of the most common and 
familiar of physical phenomena. Common and familiar as it is, 
however, there are circumstances connected with it, which render 
it not merely curious, but highly interesting, and which have 
attracted the attention of many celebrated natural philosophers. 
A number of facts have accordingly been well ascertained, and 
in explanation thereof, various theories have been proposed,— 
built, all of them, more or less ostensibly, on hypothetical bases. 
Electricity, radiation of heat, frigorific rays, and aerial pulsa 
tions, have each had their full share of attention. It is not the 
present object to attempt to decide on the individual merits of 
these theories, but rather to draw attention to some facts and 
circumstances which seem to merit farther consideration. 
1. A number of experiments were made by Dr Wells, and 
more recently by others, on the condensation of aqueous vapour, 
by exposing pieces of gilt or silvered paper in the open air, after 
sunset. ; Now, though paper thinly coated with a metal, may be 
well fitted for experimenting on the spontaneous condensation of 
moisture, when the object is to ascertain the modifying effects 
of certain combinations, surely nothing could be less accurate 
than to reason upon such experiments, as if a thin plate of metal, 
and paper thinly coated with metal, were one and the same 
thing. Paper is one of the worst conductors of heat, and is, 
besides, highly susceptible of being influenced by atmospheric 
humidity. Hence, when placed in close contact with a sheet of 
* Bibliotheque Universelle, July 182-5. 
VOL. XIV. NO. 27 - JANUARY 1820 = E 
