W. M. Harrington—Brief Study of Vesta. 461 
the direct effect of centrifugal force, and it is presumed that 
the error resulting from this omission is not very great. Since 
the pressure and temperature of the air corresponding to the 
different wind velocities is not given, we are obliged to neglect 
the influence of these terms. The latitude of Kew is 51° 28’. 
Under these conditions Ferrel’s formula becomes 
G = 0°1558:, 
from which are deduced the values in column third. These 
values (with the exception of the last) are all less than the ob- 
served gradients shown in column second. If we multiply 
each of the numbers in column third by 1°64, we obtain the 
numbers in column fourth. The differences between the num- 
bers in column second and those in column fourth, are shown 
in column fifth. It will be scen that for velocities of the wind 
greater than twelve miles per hour, the corresponding gradients 
in column fourth are less than the observed gradients; but for 
velocities less than twelve miles per hour, the gradients. in 
column fourth are greater than the observed gradients. The 
differences shown in column fifth may in part be ascribed to 
=e factors of the formula which we have been obliged to neg- 
ect. 
These results confirm the conclusions previously stated in 
this paper, and appear to demonstrate that the principles of 
F errel’s formula are correct, except that the effect of friction is 
considerably greater than he has supposed. 
_ lhe preceding paper was written and presented to the Na- 
ional Academy of Sciences last April, but its publication has 
been delayed by sickness. 
Art. LL—A Brief Study of Vesta; by M. W. Harrineron. 
Ir has long been suspected that several of the asteroids have 
variable light, but so far as I know they have not been studied 
With reference to this point except by Ferguson over thirty 
years ago. One of the tasks which I have desired to under- 
Vesta and 2163 each, five observations of extinction in as rap 
. 
i 
Succession as possible. The mean of the five extinctions of 
