92 MASS. EXPERIMENT STATION BULLETIN 160. 



occur until after the bog had been reflowed (no reflowing whatever had 

 been done between June 26 and September 11), it seems probable that 

 the effect of the flooding partially remained with the bog in some way in 

 nights following those in which the flowing was done. Before the flood- 

 ing, both the sand of the bog and the adjacent low land were unusually 

 dry. The flooding left the bog in a condition of normal moisture, while 

 the low land remained abnormally dr3^ This was apparently all that 

 could have had any effect on the difference in temperature between the 

 two locations. It seems evident, therefore, that moisture in the soil tends 

 to maintain a higher air temperature above it on cold nights than would 

 be had without it. That this is true is borne out further by the records 

 of the latter part of September and the first part of October. On the 16th, 

 the difference in the minimum temperature of the two locations — above 

 mentioned — was 4i^°; on the 17th, 3° (possibly so little because of 

 failure of one thermometer to record properly); on the 18th, 4°; on the 

 20th, 6°; and on the 30th, 5°, these dates being selected because their 

 nights alone were cold. Before any October records were made, over 

 half an inch of rain fell, which, of course, did much to bring the soil of 

 the low land back to a normally moist condition. After this rainfall the 

 difference in the minimum temperature between the bog and the low land 

 ranged from li/o° to 31/2°, being distinctly less than it was before the rain 

 came. 



Acting on the suggestion obtained from these observations, that an 

 increased water content of the soil tends to raise the minimum air tempera- 

 tures above it on cold nights, the writer had two circular grassy areas 

 (of between 2 and 3 square rods each) covered to an average depth of 6 

 inches with as dry sand as could be obtained in any quantity, between 

 September 20 and 25. A Green minimum thermometer was placed over 

 the center of each of these areas. On the nights of both September 26 

 and 27, these thermometers showed a difference of half a degree in their 

 minimum readings. On September 28, the spot which had showed the 

 lower minimum temperature on the two previous nights was wet down 

 thoroughly with water, the wetting being done between 10 a.m. and 

 2 P.M., the temperature of the water used being 51° (pumped from a driven 

 well 22 feet deep) and that of the sand on the other spot ranging from 

 51° to 52° at noon. The temperature of the air 6 inches above the center 

 of the spot not wet down was 52° at 11 a.m., and that of the water in the 

 ditches of the station bog at the same time ranged from 53° to 55°. In 

 the cold nights following soon after, the thermometer over the spot that 

 had been wet down recorded a minimum temperature from half a degree 

 to a degree higher than the other one, the result of the test thus corre- 

 sponding in a general way to that of the observations in connection with 

 the bog and low land thermometers. Great reliance, however, cannot be 

 placed on this result because of the small size of these test areas. 



While the results of this investigation are not conclusive, thej' raise 

 a question of no little importance, for if the moisture content of a soil 

 affects the minimum temperatures of the air above it to any considerable 



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