Section 7. Every lighter or other vessel employed in transporting stone sold by weight or gravel or sand shall be marked on the stem and stern post, nearly level with the bend of the vessel, with stationary marks or bar iron, not less than six inches long and two and a half inches wide, fastened with two good and sufficient iron bolts driven through said stem and stern post and riveted into said bar iron, from which all other marks shall take their distance in feet, inches and parts of inches, as the distance may require, from the lower edge of the stationary marks to the lower edge of the other marks; which marks shall be as follows: light water marks, not less than four inches long and one inch and a half wide; and marks for every four tons above said light water marks, legibly cut or cast, in figures of four and multiples of four, up to the full capacity of the vessel. Said figures shall express the weight which such vessel is capable of carrying when the lower parts of such figures touch the water; and all the marks shall be of good and sufficient lead or copper, fastened on the stem and stern post of each vessel with sufficient nails not less than one inch long; or the weight which such lighter or other vessel is capable of carrying shall be indicated by having in the hold of such lighter or vessel, at each end thereof, and as near as practicable to the extremities of the space where the cargo is usually carried, a glass tube, with a stopcock at the bottom, which shall be mounted upright upon a scaleboard of metal or wood having marks or figures so arranged thereon as to indicate the weight of the cargo when the water in the tube shall reach the bottom of a figure or mark on the scaleboard.