506 REPORT OF THE COMMISSIONERS OF 



the period of thirty-three years was 1.03 inches greater tlian the mean rainfall for 

 the Sudbury for twenty-one years. The mean run-off of the Cochituate for the same 

 period was 20.40 inches, as against 22.26 inches on the Sudbury ; or in spite of the 

 fact that the mean rainfall of the Cochituate was 1.03 inches greater for the periods 

 considered than that of the Sudbury, still the mean run-off of the Cochituate was 1.86 

 inches less than that of the Sudbury. For the Mystic the rainfall was 44.07 inches, 

 run-off 19.94 inches, and mean evaporation 24.13 inches. 



The temperature records at hand for these three drainage areas are not entirely 

 satisfactory, no record having been kept for the Sudbury and Cochituate previous to 

 1 88 1, since which time a record has been kept at South Framingham. In order to 

 fill out the tabulations complete, the temperature record used previous to 1881 is that 

 kept at Cambridge, Massachusetts. Basing our conclusion on such data we obtain 

 a mean temperature for the Sudbury drainage area of 47*^ F. ; for the Cochituate area, 

 a mean temperature of 47.7'' F. ; for the Mystic area we have a complete record 

 from 1 8 78 to 1885, inclusive, and for the balance of the time I have used the 

 Chestnut Hill reservoir record, whence we obtain a mean temperature of 48.5° F. 



A study of the detailed records on a number of different lines has thus far failed 

 to show for these three areas any clear relation between temperature and run-off. 

 The indications, on the contrary, are, as might be reasonably expected when one 

 studies the question broadly, that there are a number of other elements of so much 

 importance as to make temperature only of secondary importance. It is not intended 

 to say, however, that there is not some relation between temperature and run-off; but, 

 it is intended to say, that Mr. Vermeule's conclusion that the whole matter is simply 

 one of relation of temperature is so far from the fact as to in effect invalidate any 

 conclusion he may have put forth on the subject under discussion. 



In regard to the persistency of the evaporation element we may note that on these 

 three Massachusetts drainage areas the evaporation groups itself at about the same 

 point. For the Sudbury, the mean evaporation for the whole period considered is, as 

 shown, 23.60 inches. The minimum year of the whole period considered was 1883, 

 when the run-off for the storage period was 9.70 inches; for the growing period, 0.86 

 inches; and for the replenishing period 0.84 inches, giving a total of i 1.40 inches for the 

 whole year. The rainfall that year was — storage period, 16.78 inches; growing period, 

 5.61 inches; replenishing period, 893 inches, giving a total of 31.32 inches for the 

 whole year. Even with a rainfall of only 31.32 inches in 1883, still the evaporation 

 rose to 20.12 inches, or to only 3.48 inches less than the mean, while the rainfall for 

 the same year was 14.34 inches less than the mean. If we trace out the figures of 

 the Cochituate and the Mystic areas we shall find the same interesting fact, namely, 

 that in years of low rainfall the persistency of the evaporation element is such that it 



