1873.] Memorandum for guidance of the Yarhand Mission. 125 



greater richness of animal and vegetable life in those regions, and because it 

 is intimately connected with evaporation. The existence and nature of 

 saline deposits such as Borax, Salt, Carbonate of Soda, &c, should not be 

 overlooked in connection with this subject. The extent, flow, and progress 

 of glaciers should be noted. 



The party should be supplied with the instruments necessary to make 

 these observations, and also with a suitable instrument, by which the evapo- 

 rating power of the air can be, at least approximately, determined at differ- 

 ent elevations in the valleys and on large glaciers. 



Meteoeology. — Whether Meteorological observations can be taken with 

 any degree of fulness must depend greatly on the means of transport. If 

 these do not admit of instruments being taken, other than such as are 

 most compact and portable, it will be necessary to restrict the observations 

 to the temperature and humidity of the air, to the direction and estimated 

 force of the wind, the occurrence of rain, and the forms, quantity and move- 

 ments of the clouds : but if the means of carriage suffice, a barometer, radia- 

 tion-thermometer, an anemometer and an actinometer should be taken, and 

 also a small rain-guage. The chief points to which attention should be given 

 are the following : 



1. The diurnal range of temperature in the shade ; which may be ex- 

 pected to be very great in so dry a country. Care will be required in select- 

 ing a proper place for the thermometers to guard them from being affected 

 by direct radiation to or from the clear sky. 



2. The minimum temperature of radiation at night should be observed 

 whenever possible by a thermometer placed on the ground, and fairly expos- 

 ed to the sky. In taking these observations, it is necessary, if the ground is 

 not level, to place the instrument in a slight hollow or on black woollen 

 cloth in a shallow box, or it will be affected by the convection of the air, 

 and show a temperature many degrees higher than one protected from this 

 influence. It is probably greatly owing to this cause that the registered 

 temperature of nocturnal radiation at certain of the Himalayan stations ap- 

 pears to be but little below that of a shaded thermometer. 



3. Any observations of tbe absolute heating power of the sun will be 

 very valuable, since the dryness of the air is such, that its absorption of solar 

 heat must be small. At such times particular attention should be paid to 

 the clearness of the atmosphere from dust, since if a dust haze prevails to 

 any great height, the absorption of solar heat by the atmosphere may be 

 very considerable. If the means of transport do not allow of an actinome- 

 ter being taken (Hodgkinson's is the best) the maximum heat of the sun, 

 taken by a black bulb thermometer in vacuo, will be valuable. 



5. Observations of barometric pressure will probably be made for the 

 determination of heights. If possible, a few sets of hourly observations ex- 



