CLIMATE. 73 



current of wind prevailing, from one quarter or another, at 

 that time. About ^ past 8 or 9 A. M. is the time when the 

 sun's rays appear to have most power, the air being then still, 

 and its capacity for heat having been diminished by the in- 

 crease of density arising from the cold of the succeeding 

 night. This it is important for invalids to observe, as well 

 as the sudden chill produced by the sinking of the sun below 

 the horizon in the evening, when the column of rarefied air 

 next the surface rises aloft, and is rapidly replaced by a colder 

 stratum from above. 



The minimum generally occurs about ^ an hour before 

 sunrise, when, as before observed, the lower valleys are gene- 

 rally filled with fog. 



During the monsoon season, when the sky is covered with 

 clouds, at once diminishing the power of the sun's rays and 

 obstructing the effect of radiation from the ground, the tem- 

 perature is remarkably equable, the range seldom exceeding 

 12° or 14<* in the open air, while in rooms, without a fire, it 

 is under 4° or 5° . The thermometer attached to one of my 

 barometers, kept in a small sleeping room without a fire-place, 

 (though the house itself was rather exposed,) during the 

 months of May, June, July, August, and September, 1831, 

 never fell below 59°*5, nor rose above 62<*. This is, therefore, 

 notwithstanding many drawbacks, much the most favorable 

 season for invalids, and should be selected, when a power of 

 choice exists, as the period for ascending the hills. 



Photometer, The effects of the radiation of the sun's rays 

 appear to have attained their maximum on the 18tli January, 

 when the photometer indicated 126, that is, the calorific 

 effect of the sun's rays was equivalent to 22*'*68 Fahrenheit. 

 The minimum appears to have occurred on the 27th August, 

 when the increase of temperature was only equivalent to 9", 



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