in length. But as the engineer will have to measure many not of his own taking, he should have a rule divided into hundredths.

The annexed diagram was measured by the planimeter, and gives the following results: Area, 1.34 square inches; 1.34 multiplied by 40 the scale 1.9818, the M. E. P.

The area of a figure may be taken without placing the O on the roller opposite the O on the vernier; but in such cases it is necessary to take the reading before and after the tracing is made; the difference between the two readings will be the area of the figure. But it is preferable to place the O's together. The movable point of the instrument may also be turned to the left, but in this case the reading must be subtracted from 10 to give the true reading. Each of the figures stamped on the roller indicates a square inch of area, and if a figure contains 10 square inches at the tracing-point, the roller will revolve once, and the O's will coincide as at the start.

Hardly a "decade" has passed since the days of Newcomen, which has not witnessed the promulgation of some vague scheme which it was claimed would revolutionize the economical working of the steam-engine, or even do away with it entirely, and super

sede it by something else. Such wild schemes have invariably proved failures, as they must ever do, because there are some principles involved in the working of the steam-engine which, according to the natural order of things, can never be disproved. Consequently, those who intend to purchase steam-engines, or those who have capital invested in them, need entertain no fears that steam as a motive-power, and the steam-engine as a motor, will ever be superseded by anything else, while efficiency and economy are desirable objects to be attained.

Nor has there been any new principle discovered in connection with the steam-engine since "Newcomen's" time, as Watt, Hornblower, and Oliver Evans knew just as much about the latent and sensible heat, temperature, and the elastic force of steam as we do; though they lacked the knowledge of applying it so economically to the piston. This did not arise from ignorance of its properties so much as from the want of proper facilities to apply it. Nor is it at all likely that the steam-engine of the present day will ever be much improved upon in point of economy or efficiency, though it may be in point of durability. Good material, good tools, and perfect workmanship will go far towards the economical working of the steam-engine. It is a very noticeable fact, that no important improvement has been made in steamengines of any kind within the past 15 years. To be sure, there have been many innovations introduced in that time, but upon examination it will be discovered that, in nearly all cases, they were a revamp of things which had been used before, and abandoned for want of experience in their use and proper facilities for perfecting them.

The mean effective pressure on the piston of a steam-engine is the exponent of the work performed. The term "effective pressure" means the amount by which the total pressure behind the piston exceeds that which acts on the other side in opposition to its movement. The terminal-pressure, or that at which the steam is released from the cylinder, is the corresponding exponent of the consumption of water by the engine or the cost of the power.

Hence, the best economy is attained when the mean effective pressure is highest relatively to the terminal-pressure, and anything that will increase the former without correspondingly increasing the latter, or which will diminish the latter without correspondingly diminishing the former, will improve the economy.

The amount of water consumed by an engine is the only intelligible criterion of the economical results it is capable of producing. The amount of fuel consumed will depend upon the kind of boiler used, its condition as to dirt, scale, etc., the manner in which it is set and fired, the quality of fuel used, the draught, and numerous other conditions; while the amount of water used will depend entirely on the engine, provided that it is furnished with dry steam. The theoretical rate of water consumption, as deduced from the diagrams, can never be realized in practice. A certain amount will always be lost from condensation, leakage, and unevaporated spray in the steam, for which no process of calculation. can make allowance.

Now admitting that the evaporative efficiency of steam-boilers, under the best conditions, is 8 pounds of water per pound of coal, providing the water consumption of an inferior type of engine is one cubic foot, or 62 lbs., it would require 73 lbs. of coal, or its equivalent in other fuel, to develop a horse-power; while an automatic cut-off engine would yield a horse-power with a water consumption of 20 lbs., and the consumption of less than 3 lbs. of good coal. If an inferior type of engine require the consumption of 5 lbs. of coal per horse-power per hour, and an improved engine produce the same power from a consumption of 3 lbs., the latter will effect a saving of 40 per cent. in fuel over the former. Such comparisons may be considered extreme, but this is not the fact, as such cases are quite common in every manufacturing district. A manufacturer at Detroit, Michigan, was induced to take out an engine, which he was influenced to believe was wasteful, and replace it with one that was represented to be very powerful and economical, and at the same time very cheap. The engine was represented by the manufacturers as being capable of de

veloping 100 horse-power; but it utterly failed to come up to this representation. When the indicator was applied, it showed that the engine was developing only 60 horse-power. The coal consumption was found to be nearly 8 pounds per horse-power per hour.

The great Lancashire (England) strike which occurred during the present year, and resulted in a loss to both employers and employees of several millions of pounds sterling, was brought about by an attempt on the part of the manufacturers to reduce the wages of the operatives one cent on every ten yards of manufactured cloth. They defended their action on the ground that ten per cent. was all the profit they realized on their manufactured goods, and stated that, unless the operatives would submit to the reduction, they would have to discontinue their business. Nevertheless, it had been well known for years, by reports made to the Lancashire Institute and the officers of the Midland Steam-Users Association, that there were thousands of steam-engines in that county, supplying power to factories, that were consuming from eight to nine, and in some cases ten and a half, pounds of coal per horse-power per hour, and yet the manufacturers could not discover any "leak."

Before purchasing an engine or any other machine, there are some very important points to be considered which involve its commercial value, among which are, the amount which it would save or earn over another machine when in use, the time it would run without repairs, or the addition of any expenditure to its original cost. For these reasons, the conditions that should guide steam-users in the selection of engines are steady motion under varying circumstances, economy of fuel, and cost of maintenance. In the best types of the steam-engine, the principal expense, besides first cost, is fuel; but in inferior classes of engines, the cost of maintenance, such as lining up, and renewal of the different parts, increases annually, until in a few years the cost in many instances exceeds that of the fuel. It is to such considerations as these that steam-users should direct their attention when about to purchase steam-power, or replace a worn-out engine with a new one.

It has not always been the custom heretofore for those needing steam-power to purchase the most economical engines, but rather to buy for the lowest possible first cost, regardless of future maintenance. Manufacturers of inferior steam-engines being aware of this, agree to sell an engine of a certain horse-power for a certain price, perhaps 25 per cent. less than would be asked for a first-class machine.

Many persons are under the impression that it requires more fuel to carry steam at 100 lbs. per square inch than at 50 lbs., which is evidently a mistake, for while it requires a slight addition of heat to raise it from 50 to 100 lbs., the expenditure is more than compensated for by the superior expansion of the steam. Of course, the radiation will be greater at a 100 lbs. pressure per square inch than at 50 lbs.; but this would be more than overbalanced by the saving in the consumption of steam; as steam at 70 lbs. pressure per square inch will perform more than seven times as much duty as steam at 25 lbs. pressure.

Another fact not generally as well known to engineers and steam-users as it ought to be, and which illustrates the benefits to be derived from expansion, is, that if an engine was taking steam whole stroke, or 1 of the piston-stroke, with say 60 lbs. pressure per square inch, if the pressure is raised to 75 lbs. per square inch and cut off at stroke, the engine would do the same amount of work.

Location of Steam-Engines.

There is no class of machines, save, perhaps, steam-boilers, that are so often injudiciously located as steam-engines; they are not unfrequently stowed away in out of the way places, without any regard being paid to their general appearance. This arises from the fact that persons consulted on such matters are allowed to locate steam-engines who are totally unfit to do so, on account of a want of that practical skill and experience that should be possessed by persons who undertake this duty.

It is a mistake to locate an engine at the extreme end of a