Wind north, a light breeze, a large halo visible about the sun.
January 15th, 1821.

Observed an apparent meridian altitude sun lower limb 4 degrees 24 minutes 57 seconds.

Sun apparent diameter 31 minutes 5 seconds.

For apparent altitude 4 degrees 24 minutes 57 seconds the mean refraction is 10 minutes 58 seconds (Mackay's Tables) and the true, found as detailed above, is 14 minutes 39 seconds which, increasing in the same ratio as that of the atmosphere at a mean state of temperature, is 43 minutes 57 seconds at the horizon.

But the difference of refraction between the upper and lower limbs increasing also in that ratio gives 48 minutes 30 seconds for the horizontal refraction.
Temperature of the air minus 35 degrees, a light air from the westward, very clear.
The extreme coldness of the weather rendered these operations difficult and dangerous; yet I think the observations may be depended upon within 30 seconds, as will appear by their approximate results in calculating the horizontal refraction, for it must be considered that an error of 30 seconds in the refraction in altitude would make a difference of several minutes in the horizontal refraction.