I take the liberty to enclose you a number of Altitudes, which I calculated in the month of August last, from Barometrical observation, and which I hope Will not be unacceptable to you. These, together with those I have already sent you, Will I presume afford you a pretty accurate knowledge of the absolute, as well as relative, heights of the principal mountains in the northern Section of our Country.1 It is my intention as soon as circumstances Will permit, to add to these two more Peaks of the Green mountain Range (Mansfield-Mountain and Camels-Rump) which are thought by several Persons, to equal if not exceed Killington Peak in height. In the month of June 1816, I made an excursion to Sandy Hook, in Company With Doctor Mitchell and several other Scientific Gentlemen, for the purpose Of ascertaining the Altitude of the high-lands of Neversink, situated in the County of Monmouth state of New-Jersey, and a celebrated land-mark for vessels coming in from the South; I made the observations, with a new-Barometer of Dollond’s construction, and Graduated to the one thousandth part of an Inch. The most elevated part of those Highlands (Mount Mitchell) I found to be 282 feet above high-Water mark, and Canello-Wood-Hill—another Peak, 272½ feet. The determining Those Heights accurately Though a trifling operation in itself, Will, I am inclined to believe, be of considerable importance to Navigation. Doctor Mitchell informed me, that since his remembrance, There have been about twenty vessels lost in attempting to enter the Harbor of New york, in consequence of running aground off those Highlands, and when The masters of those vessels, supposed They were at such a distance from shore as to be perfectly safe. The principal cause of those Accidents, I believe is now Well understood. Those High-lands—previous to June 1816—had been estimated to be 600 feet high, and were so entered on The American Coast-Pilot Edited by Mr Blunt. The consequences have been, That when vessels coming in from Sea, hove in sight of them, Their Commanders, by means of their tables, calculated Their distance from land, upon the supposition They were actually 600 feet in height. They accordingly supposed themselves much further from shore than they really Were, and consequently run aground before they were aware of it. The last vessel lost there, Was lost under circumstances similar to those just mentioned. The Captain declared he knew the Coast so well, That he could have brought his vessel in, in a fog or in the night. He hove in sight of those Highlands just at night and calculating his distance from land upon the supposition They were 600 feet high, and thinking himself perfectly safe, did not take the necessary precaution, The consequence Was That before morning he run aground. The true altitude is now entered in the Coast-Pilot and I hope will be the means of preventing similar accidents in future. It is a little astonishing however, That this Error should have been permitted to exist so long, when a few hours of time, and labor might have rectified it. I do think it a matter of Great importance, That all the Eminences on our Seaboard, and particularly, Those at the entrance of our Harbors, and The mouths of our rivers, should be accurately calculated—I have no doubt it would be the means of preventing the loss of many vessels. I must request Sir you will excuse this Scrawl, it was Written in Great haste—