I have recd & read your interesting communication of the 10th Novr with great satisfaction, and have laid the same before the Committee appointed on the subject of your former communication; who, I am sure, will give it that consideration which it so highly merits. In the meantime, Sir, you will permit me to make a few observations, which may not, however perfectly agree with the ideas which you have expressed on the subject.

1. I cannot perceive any satisfactory reason for rejecting the cylindrical pendulum, which you formerly recommended as a standard of lineal measure, and giving the preference to a bob-pendulum. In the former, the proportion between the whole length of the cylinder and the virtual length of the pendulum, or distance between the center of suspension & center of oscillation, can be exactly found; and such a description of it can be given in words as will enable an artist to make an accurate imitation—neither of which is the case in the bob-pendulum.

2. It is not necessary that the whole length of the pendulum should be made the unit of measure:—Any given part thereof may, with equal convenience be used for this purpose. And, on many accounts, I cannot help giving the English foot a decided preference, as the unit of long measure in the U. States; and that its parts & multiples should continue the same as they have done time immemorial. Any material change, either in the unit or division of weights or measures, would perhaps be impracticable Even in France, under the strong government of Napoleon, the old weights & measures, I am credibly informed, are still generally in use, except in their public offices.

3. Neither is it at all necessary that the pendulum should be so regulated as to make exactly 86400. oscillations in a mean solar day, in a given latitude, and at a given temperature—a problem which in practice would be very difficult to accomplish—Let a cylindrical pendulum rod of any given metal, (except iron which will be affected by magnetism) of a convenient length, (say about 5 English feet) its diameter being in a given proportion to its length, (say 1 to 120) having its center of suspension (a knife-edge) at a given proportional part of its length, (say ^{¹⁄₁₂₀} part) below the upper extremity, be attached to a good clock in any given latitude (say 40° N. which is not far from the mean latitude of N. America) at any given height above the level of the sea, at any given temperature of the atmosphere;—and by a few repeated experiments, let the number of oscillations in a sidereal day (which on many accounts should be preferred to a solar day) be carefully ascertained. Then on this pendulum-rod let the unit of lineal measure (the English foot) be marked, and its proportion to the whole length of the pendulum-rod exactly ascertained & noted—a problem of easy solution by the aid of a proper instrument. Now from the above and other well-known data, the same unit of measure may be marked on any other cylindrical pendulum, under any other given circumstances: and thus a very accurate & comparable standard of measure is easily obtained, communicable by words to distant nations or future ages.

4. Instead of opening a correspondence on this subject, with the learned societies of other nations or countries, as a preliminary step, would it not be preferrable, after sufficiently maturing the system, to bring it before our own national legislature, and induce them to give it a legal sanction? Our standard of weights and measures being thus fixed, it might be a proper diplomatic business to obtain from all other civilized or commercial nations, an exact comparison between their standards & ours.

5. I am not quite satisfied with respect to the accuracy of deducing the standards of weight or capacity from that of lineal measure; since any little, unavoidable error in the latter will be greatly increased in the former—I have therefore a scheme, tho not yet sufficiently matured, which was suggested by my son Robert, now in Europe, for a comparable standard of weight, and consequently of capacity, independent of lineal measure—It is a drop of pure water; not thro a hole or aperture, for the size of this (which could not with sufficient accuracy be described in words) would affect the weight of the drop; but from a solid conical point of pure gold of a given angle—And let any given number of these drops, at a given temperature compose the unit of weight (say that number which from a mean of several tryals would exactly weigh an avoirdupoise ounce)1—And very happily for this system, no property of a body can be ascertained with so much accuracy as its weight.

The reason why I would prefer the accustomary units, subdivisions & multiples of measure, to any other, however superior in an abstract point of view, is the strong prejudices against any innovation in long established habits & customs. This prejudice would operate powerfully with the legislature itself, in preventing them from enacting a law embracing any material innovations; but still more powerfully with the people at large against complying with such a law.

And after all, Sir, the decimal division of weights and measures, possesses no advantage over the present vulgar division, except that they afford somewhat of a greater facility in arithmetical computations.

I shall, Sir, esteem it a high favour to hear from you again on this Subject—