1882 ] H. F. Blanford — SomefurtJier results of the sun-tTiermometer. 81 



this amorphous cloud, in the driest weather, to which I would attribute, 

 in part, tlie low average temperatures of the (as recorded) cloudless months ; 

 but there is another absorptive agent, which has not been noticed bj either 

 of the autliorities above quoted, and which is certainly much more powerful 

 in dry than in damp weather, and to observers on the plains of India, 

 is not easily separable from what I have above termed amorphous cloud ; 

 since, when seen from below, it has, like the latter, the effect of lowering 

 the tint of the sky. This is the impalpable haze, which, as a general rule, 

 and always in the dry season, rests on the plains of India, extending 

 frequently to heights much exceeding 7,000 feet, and sometimes extends 

 over the outer Himalaya, in such density, that, at Simla in the months of 

 May and June, at a height of more than 7,000 feet, the hills, four or five 

 miles distant only, are sometimes almost or quite invisible. The indepen- 

 dence of these two absorbing agents is only observable at considerable 

 elevations, and in certain states of the atmosphere ; and the following 

 observation, communicated to me by Mr. J. B. N. Henessey, MA, F. R. S., 

 whose experience in actinometric work invests his observations with unusual 

 importance, is therefore especiallj^ interesting. ** You remark" he writes on 

 **.the paleness" of the sky at Calcutta. Now, last April and May, having 

 coached three of my assistants to use the actinometer exactly as I do, I left 

 them to do the bulk of the observing. The sky, at first, was quite blue ; and 

 standing on the Mussoorie ridge, the Dehra valley with the Sivaliks beyond, 

 and the plains, still further away, were all well seen. As the dry weather 

 progressed, fires, as usual, appeared in the Doon, giving rise to smoke ; and 

 this, aided by dust, gradually filled the valley and dimmed objects in that 

 direction by means of what may be called a smohe haze. The actinometer 

 however stood at 6,940 feet above the sea, while Dehra station is only 

 2,200 feet. The haze lay a long way below us ; at a guess, say 3,000 feet, 

 and, to all appearances, hanging over the Doon only. At the time however 

 a brisk south wind blows here daily, increasing in strength as the day 

 advances, so that, at first, 1 paid little attention to my assistant's remarks 

 as to the rising of the smoke, until, at last, the observations began to shew 

 inconsistencies, which, however, were complicated by the fact, proved in 

 previous years, that actinometric maximum radiation occurs before apparent 

 noon. On watching the phenomena, I saw this. Far above me, at a guess, 

 not under a mile, very thin and very light yet defined clouds were being 

 driven northwards as the wind blew. I say clouds, from want of any other 

 name ; they were white, not brown or yellow, as if of steam, with soft 

 graceful outlines along the advancing edges, which could be seen by watch- 

 ing against the blue sky. Imagine sometliing between a mist and a cu- 

 mulus, very thin and quite white. Now this steam-cloud (a mere phrase) 

 was, say, a mile above, and the smoke \ a mile below, and there was nothing 



