the balance was kept open while all weighings were being made 

 to avoid the effect of heat on the experiment. During each of 

 these days the pressure was quite constant. Feb. 28th it held 

 about 29.5, March ist approximately 29.7, while on March 2nd 

 it was 30, and during the time that the temperature was below 

 o C. for the 3rd the pressure was 29.9 so we may consider each 

 of these days as having a fairly constant barometric pressure, 

 and consequently determine the effect of temperature change 

 during each day. 



During the first day the temperature increased from -8 C. 

 to -6.9 C. while the amount of evaporation increased from 0.136 

 g. to 0.147 " P er hour. The second day the temperature 

 increased from -7-3C to -5.iC., the evaporation per hour from 

 0.149 g. to 0.164 g. The third day the temperature increased 

 from -8.iC. to -6C., the evaporation from 0.138 g. to 0.169 g. 

 per hour. 



It may be seen also that the amount of evaporation increases 

 as the atmospheric pressure increases. This is due, without 

 doubt, to the fact that the humidity of the air is less with a larger 

 pressure than with a low pressure, and it seems that the evapo- 

 ration is less on cloudy days than on partly cloudy, and less 

 when partly cloudy than when fair. At 2 p. m. the first day is 

 noticed a temperature of -7. 3 C., at the end of the hour, 

 7. i C., while the amount of evaporation for the hour is 0.143 g. 

 On the second day at 9 .and 10 a. m. we find the same tempera- 

 ture but an amount of evaporation of 0.149 S- or an increase of 

 0.006 g. per hour. On the first day from 9 to 10 a. m. we find 

 an evaporation of 0.136 g., while on the third day for the same 

 hour we have 0.138 g. evaporation. As all other conditions 

 apparently remain the same the conclusion is that the evaporation 

 increases with atmospheric pressure, or with a decrease of 

 humidity. 



The minimum temperature for each night was recorded by the 

 maximum and minimum thermometer. It was found that the 

 amount of evaporation per hour during the night is considerably 

 less than during the day the average for the three nights being 

 0.131 g. per hour while the average for an hour in the day is 

 0-153 g. 



