52 RECORD AND DISCUSSION OF TEMPERATURES. 



lent 36 inch standards, it descended after freezing as low as 44. This result is in accordance with 

 that obtained by Sir Edward Belcher, whose experiments go even farther than my own, the mercury 

 having been observed by him to descend as low as 46 below zero. 



I may mention the fact, as in some degree confirming the propriety of not excluding an eccentric 

 result from the computation of means, that two or more instruments may agree well together and still 

 differ considerably from the most probable temperatures. This was the case with two long spirit ther 

 mometers, which never, even at the lowest temperatures, showed differences amounting to one degree, 

 but which, at 68, varied 7. 7 from the mean of eleven others. The cause was in this instance easily 

 explained. The two instruments were fac-similes of each other; any errors of division of the scale, or 

 from the unequal contraction of the fluid, which was the same in both, and the same in quantity, and 

 probably taken from the same preparation of spirits, were of course common to both. The error induced 

 by the coloring matter of the fluid adhering in small particles to the sides of the tube became very marked 

 at low temperatures. Our routine of daily observation was as follows: Two 36 inch register spirit 

 thermometers were noted hourly, as well as a varying number of instruments of smaller size. For pur 

 poses of comparison, the long spirit thermometers and from five to twelve of the others, in selected 

 groups, were generally read at the same time. The difference between the mean of these observations 

 and the reading of any one instrument, gave the correction which was applied to that instrument in 

 order to get the true or most probable temperature. 



