338 
[Assembly 
surement. The justness of this opinion may be inferred from some 
remarks that may follow. If the circumstances of the two measure- 
ments were similar, in regard to the delicacy and exactness of the in- 
struments, the positions of the stations, and the number of observa- 
tions, 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 near- 
ly the same longitude, while mine differed in this respect probably 50 
minutes ; but they had the disadvantage in their remoteness, mine be- 
ing about 40 and his 100 miles asunder. The most important circum- 
stance 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 Cham plain. The altitude of Mount Marcy, ac- 
cording 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 greater 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 rail-road that he 
was exploring, the relation between them being remote and incidental. 
This presumption is strengthened, moreover, from his manner of exe- 
cuting the measurement. His estimating the distance to the mountain 
from a map, instead of deriving it from an accurately established base, 
connected with his acknowledged skill in his profession, furnishes abun- 
dant evidence that strict topographical accuracy was not his object. 
Between what limits, then, may the trigonometrical result be depend- 
ed upon ? Mr. Johnson has deprived his measurement of a requisite es- 
sential to confidence as an exact operation, in leaving us totally ignorant 
of the position in space of his point of observation, of the distance that 
he actually used, and of the number and values of the angles that he 
observed. His estimate of distance, on the authority of the old survey 
