I received, not long since, a letter from the Secretary at War requiring me to rejoin the Corps of Engineers, in which I have the honor to hold a commission of Lieut. Colonel.

In respect to this requisition, I would beg leave to observe, that I have never voluntarily absented myself, for an hour, from that Corps. My acceptance of the office of Surveyor General, proposed to me without any solicitation on my part, was the result of a condition implied, if not explicitly made by the late chief magistrate, that I should retain my rank in that Corps without any emoluments. My subsequent promotion, & various other circumstances evince, that it was not only the intention of the President, that I should hold my place among the Engineers, but derive all the advantages (emoluments excepted) of one actually in service. Though I feel the strongest impulse of gratitude for the many favours gratuitously conferred on me, I cannot consider the retention of my place in the Engineer Corps, otherwise than as a matter of right. For the President, who is at the head of the Corps, can order any individual of it, on any service, at his own discretion. When thus detached he cannot be supposed to be liable to other calls, or those of the ordinary service; nor does it belong to him to make a choice of the kind of service, in which he shall be engaged; unless it be previously submitted to his volition.

As an Officer of the U. States, in either capacity, I will cheerfully obey any orders or directions, which I may receive from my Superiors, but if it be left to my own choice to determine whether I shall hold my present situation, or remove to the Corps of Engineers, it would follow, I should suppose, that my Own convenience, as well as the public interest, be allowed, as a Motive for my determination. Now under the circumstances of the business of this office at present, & of the situation of myself, & family, if called on for an immediate decision, there is no alternative; for it would be impossible for me to be prompt in the Obedience of military orders, unless by a dereliction of plans of public service just commenced, & a total derangement of my private concerns. The Amount of orders to me for immediate service, is to allow me no choice. My passionate fondness for the Engineer Department, & the expectations, I have cherished of devoting the latter parts of my life to scientific pursuits for public advantage, must be sacrificed to an impossible condition. It is true, the Secretary at War does not require an immediate compliance with his orders, & in this I must do justice to the delicate consideration, he has afforded to this subject. But a state of suspence, is, of all others, the most unpleasant, & this to me is rendered more so, as I do not know in what light the Government views this matter, or what motives may have given rise to the requisition, except, that in the present situation of National affairs, the public service requires the aid of every individual of the Corps of Engineers. I am far from wishing even if the laws should render that Corps more numerous, for any length of time to come, to hold a place nominally, as heretofore; but since that has been the case for 6 or 7 years, I cannot perceive any great disadvantage arising from a continuation of this arrangement for a few Months. I think, a longer time, than from this to Midsummer, will not be necessary for me. It was my expectation, that this point could be decided before now, but it has been found impracticable. I must, therefore, crave your indulgence, so far as, to allow me, 4 months from this date, for the purpose of deciding on the point of holding, or resigning my commission in the Corps of Engineers.1 At the expiration of that time, if I hold my commission, I shall be prepared to obey Military Orders. At present, it would be impossible, without sacrifices of health, property & responsibility on my part, & I believe of the public interest as connected with a due exe[c]ution of the service in which I am engaged. I have the honor to be With the most profound respect Your Obt. Humle. Sert.