Fearing that you have many intrusive correspondants, and that I may be rank’d among the number, it is with great deference I make this little communication; which I hope you will excuse.

When I had the pleasure of being in your company (about 8. or 9 years ago, at Monteceloe) conversing on the subject of the Odomater, you asked me, if I thought it practicable to construct a machine that could lay down the platt of a road by the traveling of a carriage over it? I answered, I had thought but little on the subject; but from the few thoughts I had spent on it, I was of opinion it could be done. You replyed, you thought diferently. Since then, having been engaged in many other persuits, I thought but little more on the subject. Untill this spring, having entirely recovered from a long and dangerous indisposition acquired in the army of Norfolk in 1813; and being more at leasure to try experiments, I turn’d my attention a little more on the subject; and have at length reduced the theory to practice.—With very temporary materials I made a machine with which (being attached to the carriage wheel) I made a survey of a triangle of road, about 12 mile in Circimference, which completely answered my expectation. If it will not intrude too much on your attention, I will give a few of the out lines.

The chart is placed on a horizontal plane on the floor of the carriage The part of the machine which marks off the platt, progresses on the chart as the carriage moves. A rod, or index, placed convenient to the eye, and moved by the hand, is kept constantly pointing to the North-Star. This index being connected with the machine, and changing its angle with the carriage, at every turn of the road, produces on the chart, all the turns and angles which there is in the road.

But, altho this machine is perfect in principle, it is not so in practice; for want of a perfect index. The objections to this index are, 1st It can be used only in the night, 2d It can be used only in fair weather, 3d It can be used only in latitudes, neither too high, nor too low, 4th The North-Star is too often eclipsed by trees and other objects; perticularly in summer.

I have tryed several experiments to make the magnetick needle answer as an index; but have not been able to succeed; in consequence of the vibration of the needle produced by the agitation of the carriage. If this difficulty could be removed, I have no doubt it would be a very valuable acquisition. And what would add still more to its convenience—the ascent, and descent, of unlevel ground could be taken upon the same principle, and at the same time.

To take the ascent & descent, a pendulum would be a very good index. Altho the pendulum would be constantly vibrating, it[s] general direction would be perpendicular to the horizon. And as the plane of the chart varies from the plane of the horizon, by the ascending or descending of the carriage, so will the pendulum vary from its right angle with the plane of the chart; and mark off a track thereon, above, or below, a right line on the chart, representing the horizon

In surveying water courses, navigable by boats, or even canoes the magnetick needle would answer exceedingly well as an index to this machine if the water was still; but as the machine would receive its motion from the surface of the water, the current would defeat the object, and render it impracticable.

In surveying publick roads, with this instrument, the magnetick needle will answer very well, by the addition of one person more, to go before with a white pole; and stoping the carriage at each turn of the road, long enough for the needle to rest, and to set the index.

And this I think will be a great improvement on the common way of surveying roads; as it will be more expeditious, less expensive, and less subject to error: as the surveyor will not have to keep a reckoning—to enter his notes—and to plott from those notes. all of which are subject [to]1 error. But I have already drawn your attention too long I am affraid, from subjects more interesting—