50 PROCEEDINGS MANCHESTER INSTITUTE 



amount of valuable data has been obtained. In the chapter on 

 Climatology in Hitchcock's Geology of New Hampshire ('74), 

 it appears that for the years 1853-59, the mean annual tempera- 

 ture at the summit was 28 deg. F. The mean temperature for 

 the months of October to March, which there are practically 

 winter, was 12.4 deg. P\, that for the months of April to Sep- 

 tember being 39.7 deg. F. The months of June, July and Au- 

 gust, which may be taken as the breeding period for birds at 

 this height, averaged for the six years, 44.5 deg., 47.9 deg., 50.7 

 deg. F. respectively. These are the three hottest months of 

 the year at the summit, so that the mean temperature for this 

 period is 47.3 deg. F., with 50.7 deg. F. for the hottest single 

 month. This corresponds closely with Dr. Merriam's statement 

 ('98, p- 54) that the limiting temperature for the lower bounda- 

 ry of the Arctic zone is probably 50 deg. F. for the six hottest 

 consecutive weeks of summer. The local conditions of this 

 mountain summit, however, are doubtless somewhat different 

 from those of the circumpolar arctic region. The report on the 

 Climatology of the state previously referred to, includes an 

 interesting account of_ certain phenomena of the rigorous win- 

 ters at the summit of Mt. Washington, describing among others, 

 the remarkable frost feathers which build out into the wind 

 from any stationary object. In summer, cumulus clouds from 

 the heated valleys below often rise so as to envelop the moun- 

 tain top, or more- often Mt. Washington's head alone is 

 shrouded by a stationary cloud. It is stated that at times, the 

 whole country westward is covered with clouds, but that when 

 they have passed the ridge running directly south from Mt. 

 Washington, they are instantly dissolved, never passing beyond 

 a certain point, though moving at the rate of from fifty to sixtj^ 

 miles an hour. The wind at this altitude is frequently terrific. 

 During periods of storm, the wind at the summit is said ^o in- 

 crease steadily in velocity till it reaches its culmination, then 

 come lulls, at first only for an instant, and these continually 

 lengthen until the storm ceases. A wind velocity of 140 miles 

 an hour has been measured, and during one night, the mean of 

 four observations is given as 128 miles. Moreover, it is found 



