Thomas Jefferson Papers
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To Thomas Jefferson from David Melville, 23 January 1822

Washington City Jany 23d 1822

Venerable Sir,

It is with emmotions of extreme regret, that I am necessitated to trouble you with an inquiry relating to the causes of a phenomenon which has fallen under my observation, which I have not been able to account for satisfactorily to myself—and which I have not been able to find any body who could account for it either to themselves or me, indeed the greatest number of those of whom I have made the inquiry, doubt the existance of the facts until they are made evident to them by actual experiment and then they have generally expressed their astonishment, without being able to explain the causes in nature which produces the effect.

In order to explain my views in making the inquiry, perhaps interesting to myself alone, and to apologize in some degree for troubling you, I must enter into considerable detail, which I hope will not prove wholly uninteresting to you, Sir, since the object is to promote the public interest as well as my own.

It is a fact, Sir, with which from your local situation you may not be acquainted, that the Light Houses on the Sea Coast of the United States are rendered almost useless in the Winter season, when they are most wanted, in consequence of the congealing of the oil, which frequently causes the lamps to go out—and in consequence of the collection of frost on the windows, as well as of smoke and soot from the lamps and stoves, to the great annoyance of mariners, & the great loss of lives and property.—To obviate these difficulties is a thing which has long been wished for, and which I have long made it my studdy to accomplish. An improvement I have made in the lamps at present used in the Light Houses by which the oil is kept warm by the heat communicated to it from the flame of the same lamp, which at the same time consumes its own smoke, while the stoves may be dispenced with, and air enough admited to prevent the collection of frost on the windows of the lanterns; thus remedying effectually every difficulty complained of, and ensuring a good and perfect light without intermission.—It is very well known, and the reason is obvious, that humidity & frost will not collect on the inside of the lantern when by admiting the air, the internal, is kept nearly on an equality with the external temperature.

The phenomenon I observed repeatedly during an experiment made with this improvement, and which is inexplicable to me, is as follows; when in consequence of the air-ports of the lantern being closed, the humid air had condensed and frozen on the windows as hard as the glass itself comparritively, and so thick that no object could be seen through it, by opening the air-ports, and permiting a current of cool air to pass through the lantern and out at the ventilator at top, the frost was disengaged from the windows in a short time, although it was cold enough for a tumbler of water to freeze solid in the lantern during the same period, and I have observed repeatedly that the dryer and colder the more spedily the frost was removed. I observed also that the frost was removed uniformly from the upper panes first, and from the upper part of each pane in succession from the upper to the lower part of the window.

The phenomenon, and its natural causes may be familiar to you, Sir, and if so, you would greatly oblige me by giving me an explanation of it.

If it is an operation of nature new to you, as it is to every one I have hitherto consulted on the sub-subject, you can satisfy yourself of the reality of the facts stated, by placing a vessel of hot water near to a north window, when the air is cold enough to condense the vapours arising from the water and freeze it firmly on the glass—Then open the window one or two inches, and place a board on the inside; in such a manner as to give the current of air that passes in a cast upwards, and the frost will be removed from the glass in a short time. My desire to know the cause of the phenomenon, is to enable me to explain it to those to whom I state the fact, and for reasons that I nead not explain—after informing you that my business, here is to endeavour to make a contract with the Government to introduce my improvement into the Light Houses generally—upon which subject I have not yet made any overtures, in consequence of having been robed of my trunk on my way here, containing my papers for a renewal of which I am waiting.

I am, Venerable, Sir, Your most Respectfull and Obedt Servt

David Melville—of Newport Rhode Island

MoSHi: Thomas Jefferson Collection (formerly Bixby).

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