The following coefficients of friction during motion are here given in confirmation of the frictional resistance of an earth being an indicator of its slope of repose. They have been tabulated from different authorities, are the average results of practical experiments, and have been compared with the inclination of slopes actually assumed under the ordinary conditions of work. ───────────────────────────────────────┬────────────┬────────────────── Description of Earth or Material. │Coefficient │ Corresponding Earth upon Earth. │of Friction │ Slope. │ during │ S TO 1 = 1/F. │ Motion—F. │ ───────────────────────────────────────┼────────────┼────────────────── Damp vegetable or loamy earth │0·50 to 0·67│2 to 1 TO 1½ to 1 Clean dry shingle or ballast, nearly │0·75 to 0·80│1⅓ to 1 TO 1¼ to 1 without sand │ │ Clean wet shingle or ballast, nearly │ 0·67 │ 1¼ to 1 without sand │ │ Shingle or ballast with ordinary │ 0·80 │ 1¼ to 1 quantity of sand │ │ NOTE.—The presence of sand in gravel │ │ increases the frictional resistance │ │ because it makes it gritty. │ │ Excavated hard road metalling, cast │ 0·80 │ 1¼ to 1 into a mound │ │ Fine dry sand │ 0·75 │ 1⅓ to 1 Hard clay, slightly damp │ 0·67 │ 1½ to 1 Hard clay, damp to wet │0·40 to 0·50│2½ to 1 TO 2 to 1 Damp lias, yellow, and most upheaved │0·25 to 0·33│ 4 to 1 TO 3 to 1 clays in superficial beds │ │ Wet rubble on wet rubble, ordinary size│0·67 to 0·80│1½ to 1 TO 1¼ to 1 and character │ │ Do., do., when the surfaces are unclean│ 0·67 │ 1½ to 1 Do., do., Large to very large size. │0·80 to 1·0 │1¼ to 1 TO 1 to 1 Surfaces clean │ │ NOTE.—All rubble carefully deposited. │ │ Rough-faced granite on gravel and sand,│ 0·54 │ 1·85 to 1 both dry │ │ Rough-faced granite on gravel and sand,│ 0·48 │ 2·09 to 1 both wet │ │ Rough-faced granite on sand, both dry. │ 0·70 │ 1½ to 1 Rough-faced granite on sand, both wet │ 0·53 │ 1·88 to 1 │ │ CONSTRUCTED MATERIAL ON EARTH. │ │ │ │ Rubble masonry, or brickwork on clay, │ 0·50 │ 2 to 1 dry │ │ Rubble masonry, or brickwork on clay, │ 0·33 │ 3 to 1