A red drop at plus 42 degrees indicated that the
fluid had risen to that point or above it. At this period the daily
visits of the sun were very short and, owing to the obliquity of his
rays, afforded us little warmth or light. It is half-past eleven before
he peeps over a small ridge of hills opposite to the house, and he sinks
in the horizon at half-past two. On the 28th Mr. Hood, in order to attain
an approximation to the quantity of terrestrial refraction, observed the
sun's meridian altitude when the thermometer stood at 46 degrees below
zero, at the imminent hazard of having his fingers frozen.
He found the sextant had changed its error considerably, and that the
glasses had lost their parallelism from the contraction of the brass. In
measuring the error he perceived that the diameter of the sun's image was
considerably short of twice the semi-diameter, a proof of the uncertainty
of celestial observations made during these intense frosts. The results
of this and another similar observation are given in the footnote.*
(*Footnote. The observed meridian altitude of sun upper limb was 2
degrees 52 minutes 51 seconds. Temperature of the air minus 45.5 degrees.
By comparing this altitude, corrected by the mean refraction and parallax
with that deduced from the latitude which was observed in autumn, the
increase of refraction is found to be 6 minutes 50 seconds, the whole
refraction therefore for the altitude 2 degrees 52 minutes 51 seconds is
21 minutes 49 seconds. Admitting that the refraction increases in the
same ratio as that of the atmosphere at a mean state of temperature the
horizontal refraction will be 47 degrees 22 seconds. But the diameter of
the sun, measured immediately after the observation, was only 27 minutes
7 seconds, which shows an increase of refraction at the lower limb of 3
minutes 29 seconds. The horizontal refraction calculated with this
difference and the above-mentioned ratio is 56 minutes 3 seconds at the
temperature minus 45.5 degrees. So that in the parallel 68 degrees 42
minutes where, if there is no refraction, the sun would be invisible for
thirty-four days, his upper limb with the refraction 56 minutes 3 seconds
is in fact above the horizon at every noon.
The wind was from the westward a moderate breeze and the air perfectly
clear. 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. 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. Mr. Hood's Journal.)
The Aurora Borealis appeared with more or less brilliancy on twenty-eight
nights of this month and we were also gratified by the resplendent beauty
of the moon which for many days together performed its circle round the
heavens, shining with undiminished lustre and scarcely disappearing below
the horizon during the twenty-four hours.
During many nights there was a halo round the moon although the stars
shone brightly and the atmosphere appeared otherwise clear. The same
phenomenon was observed round the candles even in our bedrooms, the
diameter of the halo increasing as the observer receded from the light.
These halos, both round the moon and candles, occasionally exhibited
faintly some of the prismatic colours.
As it may be interesting to the reader to know how we passed our time at
this season of the year I shall mention briefly that a considerable
portion of it was occupied in writing up our journals. Some newspapers
and magazines that we had received from England with our letters were
read again and again and commented upon at our meals; and we often
exercised ourselves with conjecturing the changes that might take place
in the world before we could hear from it again. The probability of our
receiving letters and the period of their arrival were calculated to a
nicety. We occasionally paid the woodmen a visit or took a walk for a
mile or two on the river.
In the evenings we joined the men in the hall and took part in their
games which generally continued to a late hour; in short we never found
the time to hang heavy upon our hands; and the peculiar occupations of
each of the officers afforded them more employment than might at first be
supposed.
