Later, Watt patented the expansion of steam and six methods of using it; the double-acting engine; the double or coupled steam engine; the use of a rack on the piston rod, working in a sector on the end of the beam to secure a truly a truly rectangular motion; a rotary engine. He next decided to add a fly-wheel to his engines to equalize the effect at different parts of the stroke. He then devised his parallel motion; also the arrangement of cross-head and guides now universally used. He also patented the poppet-valve; also a revolution counter; the pendulum governor and mercury steam-gauge; the water glass and the steam engine indicator.

The above gives a partial list of the devices and improvements introduced by Watt into the steam engine; and, whereas we should to-day much prefer to have a modern engine rather than an engine of that day, nevertheless, it is plain that the rate of development is not at all as great as that which represents the change from the engine of Newcomen to that of Watt. That the introduction of the Watt engine to pump water from mines, and to run mills and shops, made a complete revolution in the ways of carrying on industrial pursuits is evident, and equally so that to the work of Watt is due the development of the steamboat and of the locomotive. Indeed, it was one of Boulton. & Watt's engines that Fulton placed in the Clermont, to drive it when he made his memorable first voyage up the Hudson, in 1807.

Whether, therefore, we consider railroads, or navigation, or mining, or manufacturing of any kind, or applications of electricity, we find that the steam engine has revolutionized the industry, and that no one to-day can undertake engineering work of any magnitude without having to make use of steam.

Now, without stopping to consider further what was the work of the early days-of Watt, of Fulton, of Stephenson, and of the host of other men who had a part in introducing and developing the steam engine-let us consider what have been the later developments that have been made in its use. And here we may say that the entire impetus towards an

investigation of the defects of the steam engine and the remedies therefor, has been the desire to save coal, and hence to cause the engine to do its work, and to make the boiler produce the necessary steam, with a smaller coal consumption. Economy of coal became at once an item of the greatest importance in the case of the marine engine, for every ton of coal less not only saved the expense of the coal, but also space in the vessel for carrying cargo, which was profitable freight. Indeed, in the early days of the marine engine, one of the questions raised touching its practicability was whether it was possible to carry enough coal for a long voyage. Hence it is that we find on the whole that improvements and economy were more sought after in the case of the marine than in the case of either the stationary or the locomotive engine.

Another fact that has aided in making the improvement of the marine engine more rapid than that of either of the others, is that the work done by it is more nearly constant; and, besides this, when the boat is on a long voyage the engine runs night and day, so that the fires are not put out each day, and rekindled as often.

Next to the marine engine, in this regard, stands the stationary engine, and especially the large pumping engine; although, in the case of the small pumping engine, economy of steam and hence of coal is usually sacrificed to cheapness of first cost and ease of repairs.

Why more attention has been paid, until lately, to economy of steam in the case of the large pumping engine than in the case of other stationary engines may seem strange, but the reason is probably to be found in the fact that such engines are necessarily owned either by the Government or by some rich corporation, whereas it has only been with the enormous development of manufactures that belongs preëminently to more modern times that large engines have been required to any great extent in manufactories, and even to-day we often find in use, in a large manufactory, a number of small engines in many cases in which the substitution of one large one would make a decided saving of coal.

In the earlier engines the valves were set to cut off at some definite point, and the steam supply was automatically adapted to the load on the engine by means of a throttle governor, which varied the pressure of the steam when it came into the cylinder. The first attempt to do away with the losses consequent upon the throttling of the steam was made by George H. Corliss, of Providence, who caused his governor to regulate the point at which the steam should be cut off, and, therefore, he left its pressure as it came into the cylinder undisturbed.

Though this is not one of the earliest improvements, it is, nevertheless, one that has been very far-reaching in its effects, and it is rare to-day that we find any large engines that throttle their steam, as large engines are almost invariably provided with an automatic cut-off.

Indeed, the influence that Corliss exercised on stationary engine practice was very great, and, throughout Europe and America, we find that the Corliss type of engine is very extensively used. But while much may be said in favor of the rotary valves and the drop cut-off, which are so characteristic of the Corliss style of engine, Mr. Corliss, nevertheless, was not identified to any extent with the modern compound and triple engines.

The saving that could be obtained by using steam expansively, instead of allowing it to follow the piston throughout the stroke, was recognized by Watt, and this feature is to be found among the early engines, and so deeply were. engineers impressed with it, that they began to build engines to run with shorter and shorter cut-offs, expecting to save steam thereby; but, later, attention was called by a number of engineers and others to the fact that cylinder condensation was an important item to consider, and that with very short cut-offs the effect of cylinder condensation was to bring about a waste of steam; so that, for every different engine running under definite conditions as to steam pressure, back pressure, etc., there is a certain cutoff which produces a greater economy of steam than either a longer or a shorter one.

To explain to any one not familiar with these matters

what is meant by cylinder condensation, I will say that the steam, when it enters the cylinder, is very hot; thus, steam of 100 pounds (i. e., 114'7 absolute) pressure, has a temperature of 3377, and, when it leaves, it has a low temperature: thus, if it escapes into the air, its temperature is 212°, or if it escapes into a condenser it is even less.

Now, during a given stroke, the steam on one side of the piston has been escaping into the air or into a condenser, and the metallic walls of the cylinder have been exposed throughout this stroke to this low temperature, hence they must have cooled off considerably and be very much colder than the steam which enters immediately afterwards, at the beginning of the return stroke.

When the steam enters at a high temperature and comes in contact with the cold metallic walls, its first function is to condense and heat these walls, and hence a large amount of steam is condensed in heating up the walls of the cylinder instead of performing work. Now, this cylinder condensation, as it is called, is greater, the greater the difference between the temperature of the steam when it escapes into the air or into the condenser, and that of the incoming steam, and anything that can be done to decrease that difference will decrease the loss due to cylinder condensation. If the cut-off is made shorter and shorter, the gain due to using steam expansively is soon offset by the greater loss due to cylinder condensation.

It is the consideration of the losses due to cylinder condensation that has, perhaps, more than almost anything else, brought about the more recent improvements in the steam engine, both marine and stationary, and now it is also beginning to have its effect in the case of the locomotive. There are several who claim to be entitled to the credit of first pointing out the fact that cylinder condensation exists, and it is not long since a number of articles appeared in the scientific papers claiming the credit respectively for Isher. wood, for D. K. Clark, and for Hirn. It is not of any special interest to us to settle this question.

As to the fact that cylinder condensation exists, James Watt found that the chief source of loss in the Newcomen

engine was cylinder condensation, and that was the first thing he undertook to remedy, thereby saving as much as three-fourths of the steam used by Newcomen's engine.

The thing of real importance for us, is to have a number of well-arranged and careful scientific experimental investigations to determine its amount under a variety of different conditions, so fully as to give us reliable information as to how to reduce it to a minimum.

Now, neither of the men mentioned above has made any such complete series of experiments, nor has any other one man done it, but it is a matter in regard to which, through the exertions of a great many, we are making decided progress, and the chief set-back is due to the attempts and claims of those who, ignoring the good example of Watt, make experiments in an unscientific or careless and put way, forward as true, conclusions that are not, and which, if accepted as facts, lead to costly experiments and certain failures. Nevertheless, a good deal of progress has been made, and the world is very much alive to this question to-day. The result has been the adoption long ago of the compound marine engine, and of late of the triple expansion marine engine, so that we find on almost any large steamer either a compound or a triple engine.

In stationary engine practice, the compound engine has frequently been used for water-works engines, but it is only in later years that it and the triple expansion engine have been introduced to any great extent into mills and manufacturing establishments in the United States; and it is only very recently that the compound principle is being introduced into locomotives. A compound engine is one in which the steam performs only a portion of its expansion in one cylinder, and then it enters another and a larger cylinder at a lower pressure, and completes its expansion therein. The result is that the difference of temperature in each cylinder between the entering and the departing steam is less than it is when the expansion is completed in a single cylinder, and therefore the cylinder condensation is less. In the case of a triple expansion engine the expansion is only completed in three cylinders, the