and the Psychrometer. 449 



to sea level and make a comparison at all possible, and second, 

 the conditions of moisture are so variable on mountain tops, 

 so influenced by local surroundings and by currents of air laden 

 with moisture condensed by the mountain side, so utterly dif- 

 ferent from the conditions in the free air strata at the same 

 hight, that no comparisons of any practical value can be made. 

 These considerations tend to show that the use of a special 

 table for stations up to 3,000 feet altitude is very questionable, 

 and in the present stage of meteorology a refinement entirely un- 

 necessary, especially ■ for individual observations. The addi- 

 tional labor and watchfulness needed in examining all records to 

 see "whether the table has been properly applied, and above all, 

 the extreme annoyance resulting from an attempt at interpolat- 

 ing for hight in a table, and the great danger of making errors 

 in such interpolation, far outweighs any theoretical advantage 

 to be gained, which, as has already been shown, is in itself very 

 questionable. While the table accompanying this paper is 

 applicable to the sling psychrometer, yet most careful compari- 

 sons between the sling and a psychrometer in a fairly open 

 shelter having a good exposure, have shown little or no differ- 

 ence ; this may easily be understood, since velocities of wind as 

 low as two meters per second have given as good results as 

 those five times as great. The table is applicable to all open 

 shelters except those from windows and on walls ; in such cases 

 there should be used, if possible, some means for artificial 

 ventilation. For all traveling parties and at all stations 

 where the temperature is often below freezing, the sling 

 psychrometer is on all accounts the best instrument for 

 obtaining air humidity. 



The experiments for this paper were completed last spring, 

 but it has been found impossible to study the great mass of 

 data and properly prepare it for publication before this time. 



October 12, 1885. 



