perceived, by the specimen exhibited, in what manner an occurrence of so serious a nature is intended to be obviated; namely, by the attachment within the track, that renders the regular progress of the moving power, and all the burden connected, perfectly certain.

"The machinery dispenses with a raised rim of any kind, and affords a perfect flat surface for the running wheels: these support the weight of the travelling apparatus, leaving the toothed wheel unencumbered, and freely to act in a straight or curved direction, being kept to the pitch line by the anti-friction rollers coming into use whenever required.

"Having provided for increased safety, it may be necessary here to notice that speed is the next object the inventor has had in view; and he depends on succeeding in this respect, inasmuch, as let the power employed be either steam or that of horses, neither can be used with greater effect in any other plan on a level, and certainly not in ascending an inclined plane, as the means and arrangement exhibited will admit. He anticipates no danger in travelling at the rate of eight or ten miles per hour.

"It is not on the combined effect alone of uniting speed with safety that the inventor comes before the public;—he supposes he has provided a permanency of construction not equalled, and some other minor advantages, which the limits of a circular will not allow of being particularised. These remarks are chiefly confined to that part of the design adapted for the use of steam; and as soon as the new application of horse-power can be exhibited, a fuller description will be given."

Polytechnic and Scientific Entelligence.

ROYAL SOCIETY.

(Continued from page 105.)

Thursday, Nov. 24.-A paper was read, entitled, An Account of the Construction and Adjustment of the new Standard of Weights and Measures of the United Kingdom of Great Britain and Ireland, by Captain Henry Kater, F.R.S.

The author, after stating that the weights and measures of the United Kingdom are founded on a standard, whose length is determined by its proportion to that of a pendulum vibrating mean time in London, which has been ascertained by him to be 39.13929 inches of Sir George Shuckburgh's scale, deems it necessary, on account of the importance of the result, to consider what degree of confidence it is entitled to. For this purpose it is necessary to compare this final result with those obtained in other experiments, and by different methods. Now it appears that previous to the experiments detailed in the author's paper on the subject in the Phil. Trans. for 1818, on which this result rests, another series is there mentioned, made with the same instruments, but under circumstances which occasioned their rejection, and which, owing to some remains in the instruments between the two series, which occasioned a material alteration in

the distance between the knife edges, have all the weight of experiments made with a different pendulum. The result of these rejected experiments, however, differed only two ten-thousandths of an inch from that ultimately adopted.

The author next compares the lengths of the seconds' pendulum at Unst and at Leith fort, as ascertained by him by an invariable pendulum, whose vibrations had previously been determined in London, and whose length was thus known in terms of the London seconds' pendulum, and as ascertained by M. Biot at the same stations by means of a variety of pendulums, and by a totally different method of observation-that of Borda. The results of this comparison are, a difference between the determinations of M. B. and of the author, of 0.00029 inches in excess at the former station, and 0.00015 in defect at the latter.

From this near agreement of all the results, he considers that the length of the seconds' pendulum in London may be regarded as certainly known to within one tenthousandth of an inch; while from the near agreement of the results of the French and English experiments on the length of the pendulum, he concludes that the length of the metre in parts of Sir G. Schuckburgh's scale may also be regarded as known within one ten-thousandth of an inch.

From an account recently published by Captain Sabine of his valuable experiments for the determination of the variations in length of the seconds' pendulum, he observes, doubts may be inferred of the accuracy of the method employed by him for the observations for determining the length of the seconds' pendulum in London, as well as in those which have been made with the invariable pendulum. It is asserted there, that taking a mean

between the disappearances and re-appearances of the dic is a more correct method of observation than that pursued by Captain Kater, and that the intervals between the coincidences obtained, by observing the disappearances only of the disc, would be productive of

error.

In answer to this objection, the author remarks, 1st. That with respect to the convertible pendulum, or that used for determining the absolute length of the seconds' pendulum, the disc was made to subtend precisely the same angle as the tail-piece of the pendulum, so that at the moment of disappearance, its centre necessarily coincided precisely with the middle of the tail-piece, and the difference between the moments of disappearance and reappearance is rigorously nothing; an adjustment indispensable in his method of observing, when the object is to determine the true number of vibrations in 24 hours.

2dly. With the invariable pendulum the disc subtended a somewhat less angle than the tail-piece, so that the inferred number of vibrations in 24 hours was diminished about two-tenths of a second. But experiments with the invariable pendulum being intended to be in the strictest sense of the word comparative, this constant difference will no way affect the ultimate result. But, as the most direct way to remove any doubts which may be entertained on the subject, the author has computed, from the whole of Captain Sabine's observations, the successive differences in the vibrations at the various stations visited by him, by the two methods, viz. that of employing the disappearances and re-appearances, and the disappearances alone. The results only in one instance differ so much as a tenth of a vibration, they are indifferently in excess and defect, and the mean of the decre

VOL. XI.

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pancies is exactly nothing. From this he concludes, that if the observations be made as nearly as possible under similar circumstances, the method of observing by disappearances alone, is productive of no perceptible error in practice, in experiments with the invariable pendulum; while in those with the convertible pendulum, the equal apparent sizes of the disc and tail-piece, preclude the possibility of any, either in practice or theory, from this cause.

The standard of Sir G. Shuckburgh having been found identical with that by Bird, in the custody of the Clerk of the House of Commons, adopted as the imperial standard unit of extension, the length of the pendulum already determined is fixed with the same degree of precision in parts of the imperial standard yard.

A repetition of Sir G. Shuckburgh's experiments on the weight of given volumes of distilled water, and a remeasurement of the cube, sphere, and cylinder, used by him, were found to give no material variation from his results, these being stated in terms of the mean of several standard weights kept at the House of Commons. The troy pound nearest the mean has been adopted, and declared by the legislature to be the original unit of weight under the denomination of the imperial standard troy pound.

A

The relation between this pound and the cubic inch of distilled water at 62° Fahr., bar, 30in., has been ascertained by the commissioners of weights and measures, who find that the latter contains 252.458 gr., each grain being the 5760th part of the standard troy pound.

The avoirdupois pound is fixed by assigning its proportion to the standard troy pound, so as to contain exactly 7000 such grains.

The imperial standard gallon is defined by stating its