56 
Mr. Christie on the effects of temperature on 
The character of the diurnal changes in the positions of 
the points of equilibrium is very nearly the same for each 
day, but, in taking the mean, I can only make use of the 
observations of the 20th, 21st, 22d, since on the 19th no ob- 
servation could be made at 10^ 30™, and the azimuths are all 
greater on this day than on any of the subsequent, and two 
observations were unavoidablv omitted on the 23d. 
Comparing the results with those obtained from the obser- 
vations made in doors, we find them agree as nearly as 
could possibly be expected. From table A it appears, that 
when the observations were made in doors, the westerly 
point receded from the north until half past 10 o’clock in the 
morning, and approached the north during the remainder of 
the day until about 9 in the evening ; and from table C, that 
when they were made in the open air, the westerly point 
receded from the north until about half past eleven in 
the morning, and approached it until six or seven in the 
evening, after which it again gradually receded. This is 
not a greater variation in the times of the maxima than we 
find on different days, either in the in-door observations, or 
in those in the open air. The easterly point appears to have 
receded from the north until about 10 o’clock in the morn- 
ing, when the observations were made in doors and likewise 
when they were made in the open air ; and to have approached 
it until between nine and ten in the evening in the former 
case, and until six in the latter. 
Taking, as before, half the sum of the mean easterly and 
westerly arcs at different hours during the day as the mean 
azimuths of the points of equilibrium at those hours, and sub- 
stituting these for <p in the equation (a^), 
M — F ( .00448032 + .0007664093 cos.* (p ) = 0, 
