44 



PROCEEDINGS OP THE AMERICAN ACADEMY 



ature of the cold rain and hail- that have been condensed high up in 

 the clouds and chill the air as they fall through it. The relation of 

 amount and rate of rain-fall, temperature of rain (or hail), and change 

 of air temperature, form an interesting subject for study. 



We have two valuable automatic traces of the temperature curve in 

 this storm from the Boston Water Works at Chestnut Hill, Mass., and 

 the City Engineer's office at Providence, R. I. The first curve shows 

 a rapid fall from 86° at 17.30 to 69° at 18.00, followed by a tem- 

 perature at midnight a little warmer than that of the early evening. 

 The second gives a fall from 86° to 74° during a i'ew minutes before 

 and after 18.00. 



Barometric Changes in Storm of July 9. — The self-recording barom- 

 eters (Draper's pattern) at Providence (City Engineer's office) and 

 at the Blue Hill Meteorological Observatory were both affected by 

 this storm in a similar way. The hundredths of an inch over twenty- 

 nine inches are given in the following table for fifteen-minute intervals 

 before and after the rain began. 



From this it may be said that there was a slight fall of the barometer 

 before the storm, followed by a rapid rise as the storm came on, and 

 succeeded by a fall again as it passed away. 



A composite portrait of this storm has been prepared similar to the 

 one here figured in illustration of the squall of July 21 (Fig. 6) ; its size 

 is too large to admit of reproduction. By means of a simple process 

 of construction, all the observations of wind, temperature, rain, thunder, 

 etc., are thrown in their proper relative positions with respect to the 



