120 Memorandum for guidance of the Yarkand Mission. [June, 



tending from midnight to midnight should he taken, for showing the range 

 and periods of the diurnal oscillation. At the Himalayan hill stations, the 

 morning minimum is most frequently the absolute minimum of the day, 

 which is far from being the case in the plains of India. 



It will be interesting to see whether on the more elevated parts of the 

 Himalaya and Trans-Himalayan plateaux, the oscillation follows the 

 same law as on the Indian plains or that of the hill stations. Also how the 

 epochs of maximum and minimum vary in the higher latitudes. 



6. A register of the direction and (in the absence of an anemometer) 

 the estimated force of the wind according to the Brunfort Scale, is specially 

 important. Particular attention should be given to the direction in which 

 the clouds drift. 



It is stated by Mr. Shaw that in Eastern Turkistan, the wind is chiefly 

 from the north up to the great mountain range, whereas it appears from 

 Hooker's and others' observations, that to the south of Tibet it is from the 

 south at all times of the year. It is scarcely necessary to say that among 

 the mountains, the winds are greatly affected by the direction of the valleys, 

 so that the movement of the clouds is the best criterion of that of the great 

 air currents. But any observations on the local variations of the wind will 

 be of interest. Its diurnal changes in the valleys and in the passes are worthy 

 of special observation. The violent winds from the south which blow through 

 the passes during the afternoon hours are described by many travellers, and 

 are referred by General Strachey to the heating and rarefaction of the air over 

 the lofty table-lands of the interior. 



Nio-ht winds also blow down the valleys, which are probably streams of 

 ah- cooled by radiation and gravitating like water down the hill slopes and 

 beds of the valleys. Any observation on them, the time they set in, their 

 duration and force, and the temperature of these winds will be important. 

 Also then- upper and lower limits. 



7. The humidity of the air will necessarily be very low. It should be 

 observed when actinometer observations are taken ; and whenever hourly ob- 

 servations of the barometer are made, those of the hygrometer should be made 

 also. Besides these, observations of the wet and dry bulb thermometer 

 should be taken at other times as often as practicable. The movements of 

 the clouds have already been referred to. Their quantity, forms, and esti- 

 mated height at different seasons should also be attended to. These and the 

 wind observations may be made at all times without the aid of instruments 

 other than a compass. 



Magnetic Observations. — The only attempt to procure Magnetic 

 Observations in Thibet and Turkistan of which the Council are aware, was 

 made in 1857 by the Brothers Schlagentweit, one of whom lost his life in the 

 expedition. They only made a small number of observations and none 



