256 A JOURNEY TO THE SHORES 



river here was two fathoms and a half deep, and the temperature at 

 its bottom was at least 42° above zero. This fact was ascertained by 

 a spirit thermometer ; in which, probably, from some irregularity in 

 the tube, a small portion of the coloured liquor usually remained at 

 42° when the column was made to descend rapidly. In the present 

 instance the thermometer standing at 47° below zero, with no por- 

 tion of the fluid in the upper part of the tube was let down slowly 

 into the water, but drawn cautiously and rapidly up again, when a 

 red drop at + 42° 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 ap- 

 proximation to the quantity of terrestrial refraction, observed the 

 sun's meridional altitude when the thermometer stood at 46° 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 

 j. these intense frosts. The results of this and another similar obser- 

 vation are given at the bottom of the page*. 



* " The observed meridian altitude of upper limb was 2° 52' 51". Temperature 

 of the air — 45° 5'. 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' 50", the whole refraction, therefore, for the altitude 2° 52' 51" 

 is 21' 49 ". Admitting that the refraction increases in the same ratio as that of the atmo- 

 sphere at a mean state of temperature, the horizontal refraction will be 47' 22". But the 

 diameter of the sun measured immediately after the observation, was only 27' 7", which 

 shews an increase of refraction at the lower limb of 3' 29". The horizontal refraction cal- 

 culated with this difference, and the above-mentioned ratio, is 56' 3', at the temperature 



