January 1st, 1821.

Observed meridian altitude of sun lower limb 2 degrees 35 minutes 20 seconds, sun apparent diameter 29 degrees 20 minutes.

For apparent altitude 2 degrees 35 minutes 20 seconds the mean refraction is 16 minutes 5 seconds (Mackay's Tables) and the true, found as detailed above, is 20 minutes 8 seconds which, increasing in the same ratio as that of the atmosphere at a mean state of temperature, is 41 minutes 19 seconds at the horizon.

But the difference of refraction at the upper and lower limbs increasing also in that ratio gives 55 minutes 16 seconds for the horizontal refraction.

Temperature of the air minus 41 degrees.