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Conjh'uftion of Roads.—Effects of Wheels ,

The various fafts, obfervations, and experiments, on which thefe very ufefuland interefting conclufions are founded, can only be well underflood by confult-ihg the valuable paper alluded to above ; but the refults of the differentexperiments are fliewn in one point of view, and fo arranged in the followingtable, that thofe made under a fimiliarity of circumftances, both with the coni-cal and cylindrical wheels, may be eafily brought into a ftate of comparifon.Thus the firft column, A, furniflies the number of each experiment, in the orderin which they were made, for the purpofe of referring to them when neceffary.A defcription of the particular circumftance under which each experiment wasattempted follows. The column B explains the number of weights which wererequired to draw the carriage under fuch a combination of circumftances, infuch a manner as juft to begin its motion without being affifted. And the laftcolumn, C, exhibit's, on the fcale of acceleration, the number of fpaces that thecarriage advances after the weights have ceafed to aft upon it;—which it is ob-ferved, “ by eftimating each divifion on the fcale as equal in value to one-tenthof the weights that draxc the carriage, we afcertainhow much the refiftance to the

“ A wheel twelve inches broad, will, in rolling thirty miles, cover a fpace of 158,400 feet; and the fourwheels of a waggon rolling a double furface will, at the fame rate, in a day’s journey, roll a furface of633,600 feet, which is equal to the whole furface of four miles of a road thirty feet wide, and fomethingmore than fourteen and a half acres; but rejedting fractions, and taking fourteen and a half acres as thequantity, the refult in acres will be as follows.:

2415 waggons, with 12-inch wheels, will, in a day’s journey of thirty miles,

roll ------- 35,012

3622 waggons, with 6-inch wheels, will roll ... 26,259

3622 waggons, with 4-inch wheels - 17,506

The number of acres rolled in a day by all the waggons - 78,777

" And fuppofingall the waggons, at an average, to travel only ninety days in the year, they will roll afurface equal to 7,089,930 acres; which, at one flailing per acre, will.exceed three hundred and fifty thou-fund pounds per annum.

“ But, waving pecuniary eftimates, let it,’’ fays he, “ be remembered, that the quantity of furfacethat is rolled once yearly by the waggons that travel the roads of England, is equal to the entire furface of1,948,880 miles of road thirty feet wide. It is furely then,” he thinks,“ of importance to enquire, whetherthe wheels that roll this very extenfive furface, tend to improve or impair it ? It is to be obferved, that nonotice is here taken of the waggons that are fuppofed to be employed for the purpofes of agriculture, &c».not of the immenfe number of carts, coaches, &c. that travel the public roads.”