* 



■ft 



Aixtic Ex])Ioralions. 240 



mucli interest, but he intimates that a complete report on the 

 subject and also on other points of science, including the geol- 

 ogy, will appear elsewhere, and we trust that it may yet be 

 published from his papers. 



The wide discrepancies ascertained in his spirit thermoneters 

 at very low temperatures may be considered an observation of 

 interest, as they will lead to precautions in future in the con- 

 struction of such instruments. We close by a citation on this 

 subject from the Appendix, 2d Expedition, pp. 405, 406, and also 

 a table of temperatures, p. 425. 



*' Except in naval expeditions, Ai'ctic temperatures, whether Asiatic or 

 American, have been recorded with a limited number of instruments. 

 The results of these must be received with extreme caution; for the dif- 

 ferences which alcoholic thermometers exliibit at temperatures below the 

 freezing point of mercury are so varying as to require a large number of 

 comparisons and upon many instruments, to determine their proper cor- 

 rection. It was not uncommon for thei-moraeters, which had given us 

 correct and agreeing temperatures as low as - 40^, to show at - GO^ differ- 

 ences of from fifteen to twenty degrees. Such too was the c;ise with the 

 Well-constructed instruments of Sir James Koss at Leopold Harbor. 



" To give an example of this, I may reft^a- to the record of six ther- 

 mometers, suspended near each other as above described, and observed 

 for purposes of comparison at noon, February 5, 1854, - 71*^, - 03^, - 54% 

 -53°. - oO'^ and - 50^. All of these at temperatures above -40^ agreed 

 within 1-8°, and were selected as the most consistent of nearly thirty 

 spirit thermometers. 



"At 9 A. M. of the same day, eleven similar thermometers, gave under 

 lite circumstances, a mean of 68°, the extreme readings being -56-4° 

 and - 80°. For the purpose of obtaining the most probable temperature 

 from these conflicting records, my first impulse was to reject the lowest 

 (coldest) extremes, and take the mean of those which accorded best; but 

 upon advising with our astronomer, Mr- Sontag, I determined to take the 

 mean of all, without rejecting any, — the view which he took being sim- 

 ply that those instruments which indicated the extremes in the low scale 

 tad never in temperatures above - 40° shown any anomaly which de- 

 prived them of an equal claim to confidence with the rest, and that there 

 ^as no reason a ^non' to consider the results which they gave as less 

 probable than those shown by the others. * * * * 



^ " Our thermometers were made with great care by Taliabue, of New 

 York. But, independently of other mechanical^ sources of error, I am 

 *^l>hged to say that I do not regard the contraction of colored alcohol at 

 ^ery low temperatures as sufficiently investigated to enal)le us to arrive at 

 the causes or the quantity of error. In most of the spirit thermometers 

 the uniform thickness of the tube was tested before leaving New York; 

 and the freezing- of carefully-distilled mercury which I had taken with 

 ^e for the purpose, gave excellent determinations of absolute temperature. 

 "But it may not be uninteresting to state that the freezing-point of 

 ftis metal varied between -38-5° and "41'5°, and that its rate of con- 

 traction as a solid was so uniform, that in our long and excellent 3C-inch 



SECOxND SERIES, VOL. XXIV, NO. 71. — SEPT., 1S57, 



32 



