OP ARTS AND SCIENCES. 25 



heavy rain ; four are reported about Waltham and Newtonville, others 

 in Concord, N. H,, Millville, Mass., with hail, and Middletown, Conn. 



A composite portrait (see special description of squall of July 21) 

 of this storm (June 29), prepared by Mr, Clayton, brings out with 

 much distinctness its difference from the thunder-squalls of July 9th 

 and 21st, in the absence of strong out-blowing winds in front of the 

 rain, and in the presence of a district indraft of eastei-ly winds in 

 front of the middle and northern half of the storm. Durinjj the 

 rain, no safe generalization can be made concerning the wind direc- 

 tions ; it should not be inferred from this that there is no definiteness 

 in the circulation of the wind at that time, but rather that this method 

 fails to discover it. With more numerous stations, and more regular 

 observations, there is good probability of discovering system where 

 only disorder now appears. 



June 30 and July 1. The centre of low pressure above described 

 lay over the Gulf of Maine on June 30, giving us cool weather, and 

 only three records of thunder were received for this day. On the 1st 

 of July, the centre moved northward across western Maine, with still 

 cooler weather (mean max. 64°), and no reports of local storms were 

 made: they may have occurred in eastern Maine, where we had no 

 observers. The abrupt change in the character of our weather on 

 the two sides of a centre of low pressure is thus finely illustrated. 



July 2. During the morning hours the centre of low pressure 

 retrograded into western Canada, giving us warmer weather again ; 

 in the afternoon and night it returned across northern Vermont, and 

 while there a moderate storm arose, about IT'^ to 19'^, in central 

 Massachusetts, and moved east-northeast, becoming rather strong at 

 Lancaster and Sterling at 21'', when the rain was heavy, and two 

 buildings were struck by lightning. The rain extended little farther. 

 The lightning from this storm was visible from a number of stations 

 on the northeastern coast at the above-named hour. There were a 

 few other isolated showers in the evening. 



July 3. The same centre of low pressure still controlled our 

 weather, moving on this date from Mt. Washington north to the 

 St. Lawrence valley ; and a number of separate storms appeared in 

 the afternoon in central and southern New Hampshire and central 

 and eastern Massachusetts. These local storms followed one another 

 in such close succession in eastern Massachusetts that it has been 

 impossible to trace them all. Ten of the more distinct ones are rep- 

 resented in Figure 2, moving southeast or east-southeast, at different 

 hours, their velocity averaging sixteen miles an hour. In several 



