6 . Loomis— Observations of the U. S. Signal Service. 
feeble. In No. 60 the wind at Boston at 28.3 blew from 
east, and at 29.1 from northeast, but there was no prevalent sur- 
face wind from the east quarter. The center of this low area 
passed on the south side of Mt. Washington. We thus see that 
occasionally when a low center passes near Mt. Washington 
base of Mt. Washington. In 87 of these cases the change 
occurred first at the base, and in 8 cases the change occurred 
simultaneously at the summit and the base; that is, at an interval 
of less than 8 hours; and taking the average of all the cases 
we find that the change of wind at the surface stations usually 
occurs eleven hours earlier than it does on Mt. Washington 
In 28 cases the change of the wind back from the east quarter 
to the west quarter occurred simultaneously on the summit of 
Mt. Washington and at the base; that is, with an interval less 
than 8 hours; in 16 cases the change occurred first at the base, 
and in 6 cases the change occurred first at the summit. These 
six cases were Nos. 4, 10, 48, 50, 86 and 88. In four of these 
cases the wind on Mt. Washington blew from the east quarter at 
but a single observation, while at the surface stations the east 
wind continued during a period of from three to five observa- 
tions, indicating that the influence of the movement of the lower 
stratum of the air was sensible on Mt. Washington for a few 
hours only, and then subsided. No. 88 is the only one of these 
cases in which the wind on Mt. Washington blew from the east 
quarter during more than two observations. Taking the aver- 
_ age of all the cases we find that the change of wind back from 
the east to the west quarter generally occurs at the base of Mt. 
ashington sooner than on the summit by five hours. 
If we take the average of the pressures at the center of those 
W areas in which the change of wind to the east quarter did 
the east quarter did occur on Mt. Washington we obtain 29-27 
inches, which seems to indicate that the greater the depression 
a Sa ee a el 3 ite 
