1857.] Report on tlie Progress of the Magnetic Survey. 125 



and still very nearly 2° to the east in As tor, which place was the 

 most westerly of our stations. 



It seems to be quite evident that the lines of the magnetic decli- 

 nation undergo a sensible irregularity in the mountain systems of 

 High Asia (comprising* the Himalaya, Thibet and the Kuenluen) 

 that is to say, the declination in these mountains in the same longi- 

 tude is more to the eastward, than it is in the same longitude in the 

 Indian Peninsula. 



Meteokologt. 



The barometrical and meteorological observations have been daily 

 carried on regularly as before. I may be permitted to mention a few 

 of the results. 



1. The barometric observations made at several elevated and iso- 

 lated stations (between 16,000 and 18,000 Eng. feet) hourly for 

 one or several days, have shown that the diurnal barometric varia- 

 tion at great heights in the Himalayas, is similar to that in the 

 plains ; the minimum pressure takes place between 3 and 5 p. m. 



The difference between the maximum and minimum, however, is 

 constantly very small and considerably less than it is in places of 

 less elevation above the sea. 



2. The diurnal variation of the barometer in the mountain sys- 

 tems of High Asia is therefore different from the barometric varia- 

 tion at elevated peaks of the Alps of Europe where the maximum 

 pressure takes place in the early hours of the afternoon. 



The summer heat in the valleys of BaUi, elevated only from 7,000 

 to 8,000 Eng. feet, is very considerable. I observed from the 1st to 

 the 20th July, in the valleys of the Indus and Shyok, very general- 

 ly, the following maxima and minima of temperature; maximum of 

 the day 32° centigrade, minimum of the night 15° to 16° centi- 

 grade ; average of the day 23° to 24° centigrade. 



The decrease of temperature from these heated rocky valleys to 

 the higher peaks is very considerable. 



3. The direction of the winds in western Thibet is very much 

 affected by the great local heat produced in the deep rocky valleys ; 

 regular morning and evening winds, sometimes very violent, pre- 

 vail during the summer months in the valleys of the Indus and 



