BAROMETRICAL MEASUREMENTS. 

 The followinfif are tlie observations made at Burlinijtoii : 



205 



From the little time allowed, in my first observation on the summit, for the mercury to 

 acquire the temperature of the air, and for taking the requisite precautions, the result, 47, 

 errs in deficiency. The elevation derived from the three sets is 5337*5 above tide, which 

 differs from the three results only by 12*2 and 10 feet. 



According to the barometrical measurement by Mr. Redfield and Prof. Emmons, as given 

 in the New-York Geological Report of 1838, the elevation of this peak is 5,467 feet. The 

 difference between these results is not so considerable as of itself to impair confidence essen- 

 tially in either, and they should therefore be regarded rather in the light of mutual verifica- 

 tions, at least so far as concerns barometrical measurement. The justness of this opinion 

 may be inferred from some remarks that may follow. If the circumstances of the two mea- 

 surements were similar, in regard to the delicacy and exactness of the instruments, the posi- 

 tions of the stations, and the number of observations, the mean of the two should undoubtedly 

 be taken. Not having seen a description of Mr. Redfield's barometers, I can only conjecture 

 that they were of the ordinary cistern kind ; and if so, the less perfect instruments. 



As to the stations. Prof. Emmons had the advantage of being in nearly the same longitude, 

 while mine differed in this respect probably fifty minutes ; but they had the disadvantage in 

 their remoteness, mine being about forty and his one hundred miles asunder. The most 

 important circumstance in favor of my result, is the number of observations. 



The only other measurement of this mountain, which has come to my knowledge, is a 

 trigonometrical one, executed by E. F. Johnson, Esq. a distinguished civil engineer, and 

 published Jan. 30, 1839, in his report to the New-York legislature, of his survey of a rail- 

 road from Ogdensburgh to Lake Champlain. The altitude of Mount Marcy, according to this 

 result, is 4,907 feet ; which is less than the barometrical measurements make it, by 430 to 

 560 feet. This discrepancy is too considerable to be altogether overlooked. 



The fair presumption, as it appears to me, is, that Mr. Johnson sought no gi eater degree 

 of accuracy than was requisite to convey a general idea of its elevation. This may be inferred 

 from the fact that its exact determination was a matter of no consequence to the railroad that 

 he was exploring, the relation between them being remote and incidental. This presumption 

 is strengthened, moreover, from his manner of executing the measurement. His estimating 

 the distance to the mountain from a map, instead of deriving it from an accurately established 



