This may appear a somewhat broad assertion; but it is nevertheless one which is amply justified by facts open to the consideration of all those who choose to seek for them. While it is true that occasionally a factory, mill, or a water-works may be found in which the whole arrangements have been planned by a competent engineer, yet such is the exception and not the rule, and such examples form but a very small percentage of the whole. The fact is that but few users of steam power are aware of the numerous items which compose the cost of economical steam power, while a yet smaller number give sufficient consideration to the relations which these items bear to each other, or the manner in which the economy of any given boiler or engine is affected by the circumstances under which it is run. A large number of persons--and they are those who should know better, too--take for granted that a boiler or engine which is good for one situation is good for all; a greater error than such an assumption can scarcely be imagined. It is true that there are certain classes of engines and boilers which may be relied upon to give moderately good results in almost any situation--and the best results should _always_ be desired in arrangement of a mill--there are a considerable number of details which must be taken into consideration in making a choice of boilers and engines. Take the case of a mill in which it has been supposed that the motive power could be best exerted by a single engine. The question now is whether or not it would be best to divide the total power required among a number of engines. _First_.--A division of the motive power presents the following advantages, namely, a saving of expense on lines of shafting of large diameter. _Second_.--Dispensing with the large driving belt or gearing, the first named of which, in one instance under the writer's observation, absorbed _sixty horse-power_ out of about 480, or about _seven per cent_. _Third_.--The general convenience of subdividing the work to be done, so that in case of a stoppage of one portion of the work by reason of a loose coupling or the changing of a pulley, etc., that portion only would need to be stopped. This last is of itself a most important point, and demands careful consideration.