134 PHYSICAL GEOGRAPHY. 



sunlight. Sometimes the clouds are two thousand feet below the summit 

 of Mt. Washington ; in that case, innumerable mountain peaks protrude, 

 and seem like islands in an ocean bounded only by the sky. The forma- 

 tion and the dissolving of clouds is an interesting feature. It often 

 happens that the whole country westward is covered with clouds, but 

 when they have passed the ridge running directly south from Mt. Wash- 

 ington, they are instantly dissolved, never passing a certain point, 

 although moving at the rate of fifty or sixty miles per hour, when that 

 point is reached. In spring and summer, instead of these horizontal 

 layers, the clouds assume cumulose forms, and from the mountain they 

 can be seen rising vertically thousands of feet in an incredibly short 

 space of time. During the steady cold weather of winter, the upper 

 clouds were never seen to move except in the same direction as the wind 

 on the summit of the mountain. 



Wind and Rain. 



Of all phenomena, the wind is the most terrific. Usually during 

 periods of storm, the wind increases steadily in velocity until it reaches 

 its culmination : then there are lulls, at first only for an instant, and these 

 continually lengthen until the storm ceases. The greatest velocity that 

 has been measured is 140 miles per hour; and during one night the mean 

 of four observations was 128 miles. The most remarkable fact in relation 

 to the wind is the great velocity on the summit when there is a calm at 

 the base. One observation shows that there was a wind of 96 miles per 

 hour on the summit, when, at the depot of the Mt. Washington Railway, 

 2,677 f ee t below, there was not wind enough to move the anemometer. 

 The observations were taken, under the direction of the War depart- 

 ment, during the month of May, 1872, at 7 a. m., 9 a. m., 12 m., 4 p. m., and 



9 P. M. 



In general, winds of very great velocity are usually limited to winter, 

 and to the time when there are clouds on the mountain. The prevailing 

 winds for the entire year are west and north-west. It is a noticeable fact 

 that, while the northerly and westerly winds have a much greater velocity 

 on the summit than below, the southerly winds have frequently a greater 

 velocity five hundred or a thousand feet below than on the summit. In 

 Fig. 17, the curve represents the velocity of the wind. Fig. 18 shows 



