ESSEX COUNTY. 195 



mountains have been visited, and their elevations ascertained ; and many facts in relation to 

 them, not directly connected with geology, have been observed. The annual reports contain 

 many of those observations ; and as they have been frequently copied in the periodicals of 

 the day, it appears unnecessary to repeat them here. There is, however, a communication 

 from Prof F. Benedict, of the University of Vermont, to myself, which it is my wish to 

 preserve in a durable form, as it contains much important matter which is essential to all who 

 may be engaged in barometrical observations. It is proper to remark here, that after having 

 gone over the field myself with my barometer, and ascertained the main facts, at least approxi- 

 mately, I requested Mr. Benedict to review the whole subject ; and this he very kindly did, 

 without subjecting the survey to any expense except one merely nominal. The results can be 

 relied upon, as may be seen by the steps pursued to authenticate and establish them. As 

 Mr. Benedict's communication does not admit of division or condensation, I shall copy the 

 whole as reported. 



Measurements by Mr. Benedict. 



Burlington, February 13, 1840. 

 Dear Sir, 



Agreeably with your request, I visited at two d fferent times, in the months of July and 

 August last, the sources of the Hudson, Saranac and Racket rivers, with the view of deter- 

 mining the position of that plateau which forms the base of, and extends west of the Adiron- 

 dack mountains. From the want of time and the requisite angular instruments, I was obliged 

 to have recourse exclusively to barometrical measurements. 



The instruments used at the two stations were Bunten's mountain barometers, purchased 

 by the University of Vermont, with special reference to their adaptedness to exact observa- 

 tions. These instruments are syphons, with the bores of the two legs made scrupulously 

 equal ; thus avoiding erroneous corrections for capillarity. The zero point is near the middle 

 of the scale, and the readings are from that point to the tangents of the two mercurial surfaces : 

 the sum of these gives the observed length of the column. Such is the construction of the 

 veniier, that it must be careless reading which would give an error of five hundredths of a 

 millimetre, or about two thousandths of an inch. The thermometer attached is encased in 

 the brass scale which surrounds the tube at its middle. The graduation of both the thermo- 

 meter and barometer scale is very accurate. A great variety of comparative observations 

 which I have made in comiexion with Prof. G. W. Benedict, leaves no reasonable doubt of 

 the accuracy of the graduation or uniformity of the tubes. 



Of the observations made at Burlington, to synchronize with those at the superior stations, 

 those before the sixth of July were made by Prof. G. W. Benedict, whose high standard of 

 accuracy is well known. The elevation of this station is 235 feet above Lake Champlain, as 

 determined and verified by the spirit level, or 325 feet above tide, estimating the elevation of 

 Lake Champlain at 90 feet. The observations at Burlington, after the first of August, were 



