In estimating the economy of any furnace, and the relative merits of various engines and boilers, sad mistakes are sometimes made, and the evaporator and consumer are mixed up in such a way that it becomes next to impossible to account for the steam which has been made. To remedy this, the American Railway Times suggests that a water meter be added to the boiler, and that the quantity of water which has gone into the boiler being thus accurately known, with little trouble and without any calculation, and the amount of steam consumed being measured by the indicator, the difference being known, would enable engineers to discover defects in their valvular arrangements of which they are now perfectly ignorant, and serve to show the working condition of the boiler. The indicator has done much for enabling the steam engine to be made more economical, and a water meter, simple, small and accurate, that could easily be applied to the feed pipe would be a valuable invention. This is certainly worth the attention of our inventors, and we would advise them to set their wits to work on the subject.