THE OCCURRENCE OF FROST 349 



More important, however, is the consideration that Station B during the 

 time covered by these data registered temperatures below freezing 28 times as 

 compared with 13 for Station A; Station B registered temperatures 28°F. or 

 less 14 times while this point was reached at Station A, only five times. Ana- 

 lyzing the figures in another way: in the spring of 1912 Station B had a minimum 

 of practically 28°F. as late as Apr. 26 though .Station A did not reach this figure 

 during the season. In 1913 the last minimum of 28°F. or less for Station A 

 occurred on Mar. 26 and for Station B the date was Apr. 14. 



Similar variations were found in Nevada between two points 190 feet apart 

 and differing in elevation by 13.5 feet.*^ The average April and May minimum 

 for the higher station was 42.7°F.; for the lower jt was 39.5.° On selected single 

 nights paired observations were 29-22, 34-31, 32-24, 39-31, 37-30. The diver- 

 sity in the amount of fruit grown in 2 years on sites such as these, other 

 things being equal, must necessarily be great and the difference in expense of 

 orchard heating in the two cases would be well worth considering. 



In some cases this effect is said to be somewhat neutralized by the 

 increased earliness of higher elevations. As a rule vegetation is later at 

 high altitudes, but this condition is reversed frequently between points 

 differing in altitude only a few hundred feet. An interval of 2 weeks 

 between the first blossoming dates has been reported at points in Utah 

 2 miles apart and with 200 feet difference in elevation. ^ It is not, how- 

 ever, clear that this was due wholly to the elevation since slopes and 

 condition of soil and of trees were not stated and the variations reported 

 are certainly much more marked than is ordinarily the case, making 1 

 day's difference for each 14 feet in elevation. Were the air constantly 

 still, during the whole season up to blossoming, the moderately high 

 elevations might indeed accumulate enough excess of heat to make con- 

 siderable difference but in nature this condition obtains only during a 

 very small portion of the time and such differences as do occur generally 

 may be attributed to other effects. 



The steepness of slope necessary to effective freedom from frost varies 

 with the local topography. Young^i^ states: "From observations in 

 the Pomona Valley, California, it appears that there is little if any advan- 

 tage to be gained by locating on orchard in the upper portion of a long 

 uniform slope of 150 feet or less to the mile. However, in even slight 

 depressions of whatever shape or direction on this slope the frost hazard 

 is likely to be considerably greater." 



MINOR FACTORS AFFECTING TEMPERATURE 

 Of interest chiefly to growers of strawberries and cranberries are 

 certain differences in narrowly restricted limits, differences usually small 

 but frequently important. Included among these are those due to 

 elevation, to the character of the soil covering and to the state of the soil. 

 Minor Differences in Elevation. — Observations on three sets of ther- 

 mometers at several points in Williamstown, Mass., with the upper 



