156 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



emy, read a paper on the rainfall measurements as affected 

 by placing the gauges upon the roofs of buildings instead 

 of on the ground a very complicated question, and already 

 much elucidated by the experiments at Mr. Symons's experi- 

 mental stations. As is generally conceded, the inaccuracy 

 of gauges increases when they are subject to brisk currents 

 of air. " Any obstacle placed in a stream of air causes the air 

 to sweep over the top and around the sides with an increased, 

 velocity." As a result, the drops of rain are deflected from 

 their paths and drift to leeward. Mr. Nipher has endeav- 

 ored to construct a rain-gauge so as to make it correct this 

 tendency of the drops. His idea is the same as had already 

 occurred to his colleague, Professor Woodward, and he ac- 

 complishes it by surrounding the gauge with a shield which 

 deflects the wind downward. These shields are adjustable, 

 and have been placed on several gauges whose indications 

 were, at first, very discordant, but which now are brought in 

 perfect accord with each other. 



The influence of altitude on the records of the rain-gauge 

 lias been investigated by Dines, who observed gauges at al- 

 titudes of 50 feet and 4 feet. On the average the lower one 

 caught 57 per cent, more than the upper one; in cases of 

 light, fine rain, with strong wind, the lower gauge gave two 

 or three times more than the upper one ; occasionally, in 

 heavy rains without wind, the records were alike. Dines 

 concludes that the differences are due to the wind. 



The observations made by Mr. Dines on the rainfall, the 

 direction and force of the wind, and the shape of the tower 

 in which the gauges are placed, are published in Symons's 

 "British Rainfall for 1877." Mr. Field discusses these ob- 

 servations in Symons's Meteorological Magazine^ for August, 

 1878, and concludes: first, that the ratio of the rainfall on 

 the tower to the rainfall on the ground depends on the force 

 and direction of the wind ; second, that when there is no 

 wind the amount of rainfall on the tower is about the same 

 as that on the ground; third, that when there is wind, the 

 amount of rain falling on the tower will vary on the differ- 

 ent portions of the tower; the portion nearest that point at 

 which the wind strikes the tower receives less rain than falls 

 on the ground, and the portion farthest from that point re- 

 ceives the same or more rain than falls on the ground ; 



