Where before the passing of the M1Municipal Corporations Act, 1835, a rate might be levied in a borough for the purpose of watching conjointly with any other purpose, nothing in this Act shall prevent the levying and collecting of such a rate for that other purpose solely, or affect the powers given in any Act anterior to the Municipal Corporations Act, 1835, as far as they relate to that other purpose; but where the amount of that rate might not before the passing of the Municipal Corporations Act, 1835, exceed a given rate in the pound on the value of property rateable thereto, the rate to be levied for the other purpose solely shall not exceed such proportion of that given rate as appears to have been expended for that other purpose by an account of the average yearly expenditure during the last seven years before the passing of the Municipal Corporations Act, 1835, or during those of the same seven years during which the rate was levied.