X PREFACE. 



are the results contained in the meteorological tables, they 

 can only be considered as approximations; because an uni- 

 form method of making observations has not yet been 

 adopted. Those who are conversant with thermometrical 

 observations, know what influence the situation in which 

 the instrument is exposed, and the materials of which it is 

 constructed, exercise upon the results which it indicates — 

 and how guarded we ought to be in adopting comparisons 

 made with different instruments, and placed in different 

 situations. Of the influence of the materials, the party had 

 an opportunity of convincing themselves, by placing two 

 of Mr. Keating's thermometers in the same situation with 

 that of the surgeon at Fort St. Anthony. The latter in- 

 strument consisted of a glass tube attached to a brass plate, 

 on which the graduation was marked ; one of Mr. Kea- 

 ting's was known to be a good instrument ; it had been made 

 in Paris and had its division on a slip of paper enclosed in a 

 glass tube: the other thermometer was a small pocket one, 

 made by Mr. Fisher of Philadelphia, and was provided 

 witli an ivory scale. The usual exposure of the surgeon's 

 thermometer was to the south-west. The two others were 

 placed close to his. The results are indicated in the fol- 

 lowing table. 



This proved, that when exposed to the direct rays of the 

 sun, or to their reflection by the parade ground, the ther- 

 mometer with the brass plate was uniformly ten degrees 

 higher than that made entirely of glass, though at other 

 times it stood at the same elevation. At the time these 

 observations were made, the surgeon was absent. At Fort 



