494 ON IMPRESSIONS OF COLD 
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The zthrioscope thus opens new scenes to our view. It ex~ 
tends its sensation through indefinite space, and reveals the 
condition of the remotest atmosphere. Constructed with still 
greater delicacy, it may perhaps scent the distant winds, and 
detect the actual temperature of every quarter of the heavens. 
The impressions of cold which arrive from the north, will pro- 
‘bably be found stronger than those received from the south. 
But the instrument has yet been scarcely tried. I am anxi- 
ous to compare its indications for the course of a whole year, 
and still more solicitous to receive its reports from other cli- 
mates and brighter skies *. 
All those effects are no doubt more conspicuous in the finer 
regions.of the globe. Accordingly, they did not escape the ob- 
servation of the ancients, but gave rise to opinions which were 
embodied in the language of poetry. The term Azg was ap- 
plied only to the grosser part of the atmosphere, while the 
highest portion of it, free from clouds and vapour, and border- 
ing on the pure fields of ether, received the kindred appella- 
tion of Aide. But this word and its derivatives have always 
been associated with the ideas of cold. The verb c&asbeimZm is 
adopted by Athenzeus, to signify the cooling of a body by mere 
exposure 
* In this stage of the inquiry, it may be proper to notice a singular observation, 
which I have not yet had an opportunity of repeating. An ethrioscope exposed to 
the free air, on a platform projecting towards the north, from the window of my ex- 
perimental room in Queen Street, stood a few weeks since, in a clear frosty day, at 
about 25 degrees; but, on the approach of evening, a light wind having suddenly 
turned to the opposite point of the compass, the atmosphere became at once obscu- 
red by a body of very thick and dark smoke: the liquor, contrary to all expecta- 
tion, immediately rose more than 10 degrees, and remained stationary till the 
dense mass again disapersed. This stratum of fuliginous matter would no doubt 
absorb the frigorific impressions showered from the sky ; yet being precipitated by 
its collected weight, it would bring down intense coldness from the superior re- 
gions, and therefore dart new impressions, rendered the more powerful from the 
proximity of their source. 
