HYDROLOGY OF NEW YORK 



85 



These gages were located at Chestnut Hill reservoir, in the city 

 of Boston, but the observations for wind velocity were taken from 

 the Signal Service observations, 5 miles distant. With only five 

 exceptions during the five-year period, the upper gage delivered 

 materially less water than the ground gage, the average difference 

 being 10.6 per cent for the whole period. But snowfalls and 

 mixtures of snow and rain are not included in the table of data 

 given in the paper. 



The results recorded by Professor Abbe are somewhat more 

 extensive than those presented by Mr FitzGerald, though Mr 

 FitzGerald states in his paper that he has prepared a series of 

 experiments with nine gages and a self-recording anemometor, 

 from which in the course of time some more definite results may 

 be reached. So far as the writer knows, this second series of 

 observations has not been published. 



In order to show how the catch of rainfall diminishes with 



hight of the gage, Professor Abbe gives in his table No. IV the 



results of observations at different places. These range from 90 



per cent of a gage at the ground to 47 per cent. In tables Nos. 



I, II, and III, Professor Abbe also gives the result of various 



gages, which gave 52 to 7 per cent less of 'rainfall, and from 80 to 



16 per cent less of snowfall, than gages at the ground. Professor 



Abbe remarks that these tables show conclusively the large 



influence of wind on the catch of rain, but show nothing of its 



influence on the catch of snow. As an observational method of 



obtaining the true rainfall from gage readings, Professor Abbe 



suggests the following as offering a fair approximation : 



If the present gage has been standing in an open field at a few 

 feet elevation, place two or more similar gages near it, and simi- 

 larly located as far as obstacles are concerned, except only that 

 one of these is to be decidedly lower than the old one and the 

 other decidedly higher. Prom a comparison of the simultaneous 

 records of any two gages and their altitudes, we should for each 

 separate rainfall, rather than for the monthly and annual sums, 

 deduce the normal rainfall by the solution of two or more equa- 

 tions of the form : 



Observed catch of gage=(l — x altitude) x (desired catch of normal 

 pit gage). (1) 



