correction for 1 in 10 is 78.4 lbs., therefore the friction of the surface, or what it would be if it was horizontal, would be 260-784, or 181.6 lbs. only; the difference between this and the gravel surface will therefore be 210-8-1816, or 29.2 lbs., which is equal to a saving of 4 pence for every horse drawing over a mile of such a road, as compared with the other.

4thly, The most important and useful application of the instrument is, perhaps, that of being able to ascertain with accuracy and precision the state of any road, from time to time, as regards its surface; and the state of repair in which it has been kept.

The following table, or yearly registry of a quarter of a mile of road, will show this more clearly. The numbers in the column represent the draught, or horse power, taken at every ten yards. Thus, in the first column of the year 1829, the draughts were in summer 20, 30, 25, &c., and in the second, or winter column of the same year, the corresponding draughts on the same identical part of the road are found to be 35, 35, 30, &c.: these columns added up, and divided by the number of observations, give 44.5 lbs., for the mean summer draught, and 49:45 lbs. for the mean winter draughts, over this quarter of a mile. By following the same process in the following year, viz. in 1830, the mean summer draught was found to be 35'6 lbs., and the mean winter draught 40·36 lbs., showing that the road had been improved in the course of the year very considerably; and by a reference to the numbers in the columns on the same horizontal lines with each other, it will be found the improvement has been general, throughout the whole distance. In the next year, 1831, it will be seen that the average power, in summer is

40.52 lbs., and in winter 46.5 lbs., which shows the road is not so good as it was in the preceding year, 1830, but better than it was in the first year, 1829. Again, in the year 1832, it is found that the average summer draught is 53.6 lbs., and the winter draught 63.18 lbs.: by comparing these numbers with any of the preceding years, it will at once be evident that the road has become worse; and by a reference to the figures in the column, it will be seen that it is defective in every part as compared with the preceding years, but more especially so near the end, where the draught in summer varies from 60 to 85 lbs., and in winter from 75 to 95 lbs. ; whereas, in 1830, two years before, the draughts in summer, over the same part of the road, varied from 35 to 38 lbs. only, and in winter from 46 to 40 lbs. The instrument, therefore, shows not only that the road has been getting generally worse, but it points out the particular parts, and the exact amount of deterioration; thus enabling the proper authorities to say that the road has become worse, the amount of the deterioration, and the exact part of the road where such deterioration has taken place.

The public advantages to be derived from such a system of road inspection would probably be very great. It would show not only where the best plan of repairing roads has been followed, and point out where there are good and bad surveyors, but it would also show if the money of the trust is improperly applied or wasted on any line of road; and it will enable trustees, who let the repairs of their roads by contract, to determine whether or not the contractors have done their duty, and kept the road in the same state of repair as at first, or whether they had improved it, or suffered it to become defective.

There are many other uses to which the instrument may be applied, but the foregoing are the principal

ones.

Mr. Telford, in his Report to the Parliamentary Commissioners of the Holyhead and Liverpool Roads, speaking of this instrument, states, "I consider Mr. Macneill's invention, for practical purposes on a large scale, one of the most valuable that has been lately given to the public."

Mr. Babbage, the Lucasian Professor of Mathematics in the University of Cambridge, in his valuable and wellknown work on the Economy of Machinery and Manufactures, in considering the injury which roads sustain from various causes, states, "As connected with this subject, and as affording most valuable information upon points in which, previous to experiment, widely different opinions have been entertained; the following extract is inserted from Mr. Telford's Report on the State of the Holyhead and Liverpool Roads. The instrument employed for the comparison was invented by Mr. Macneill, and the road between London and Shrewsbury was selected for the place of experiment. The general results, when a waggon weighing 21 cwt. was used on different sorts of roads, are as follow:

1. On well-made pavement the draught is

lbs. 33

2. On a broken stone surface, or old flint road - 65 3. On a gravel road

4. On a broken stone road, upon a rough pavement foundation

147

46

5. On a broken stone surface, upon a bottoming of concrete formed of Parker's cement and gravel 46."

Specimen of the Manner in which it is proposed to keep a Registry or Journal of the State of Repairs of any Road.

FROM LONDON TO

First Quarter of First Mile.

DESCRIPTION OF THE INSTRUMENT.

The framework is of wrought iron, about two feet six inches long, and eighteen inches wide. In this frame a dynamometer and brass cylinder are placed; the dynamometer is connected by its arm to one side of the frame, and the cylinder is secured in the frame by trunnions, which are cast on it, and which turn in a circular hoop or belt, firmly screwed to one side of the frame, and a bar running across it. The dynamometer, or weighing-machine, which forms part of the instrument, was introduced, some years ago, by Mr. Marriott; and as it is now so generally known, being used in mailcoach and other offices instead of the common steelyard, or scales requiring weights, it is needless to describe it here. On my applying the weighing-machine, in its simple form, to measure the draught of carriages, I found that the index vibrated so quickly, and over so large an arch of the circle, that it was impossible to observe the point indicating the force of draught; for a horse exerts his power by a succession of impulses, or strokes of his shoulders against the collar, at every step he makes, and not by a constant uniform pull, as is generally supposed. To remedy this inconvenience, and do away with the vibrations, I applied a piston, working in a cylinder full of oil, and connected with the dynamometer in such a manner that when any power or force is applied to it, so as to carry round the index, the piston is at the same time moved through the fluid. The connection of the dynamometer with the cylinder is by means of a lever working on a pivot; the arms of the lever are of unequal length; the tail-piece of the dynamometer is connected with the short arm, at a distance of two inches from the centre, or fulcrum, by means of a