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is known to be very much over or underrated, for it is almost the universal practice of American builders to design their engines to give the rated capacity at the most economical point of cut-off." It is true that the engine builders may get the proportions right in most cases, but engineers in general wish to know the average practice. The piston displacement can be determined directly from the mean pressure einployed, which for compound engines is most conveniently stated in the form of the mean pressure in the large cylinder equivalent to the sum of the mean pressure in all the cylinders. A collation of the mean pressure in connection with the economical results will, I think, show that considerably higher mean pressure can be employed than it was formerly considered possible to use with economy. In other words, the engines, or rather the piston displacement per minute, can be snaller than generally supposed.

6.

The method of arriving at the results is in some respects similar and in others different from that used by myself in 1888 in a piper on The Cost of Power in Non-Condensing Steam Engines." [Vol. X Trans. Am. Soc. M. E.] Prof. Carpenter uses in connection with his actual minimum quantity the calculated minimum quantity which he bases on a modification of the ideal engine of Carnot's cycle, which I think very properly considers only the difference of temperature between the entering steam and the exhaust. This is really founded on one of the laws of thermodynamics expressing the general fact that as the steam engine is a heat engine the most that can be gotten from it is the mechanical equivalent of the thermal units included between limits, and I think practicable, not impossible limits, should be considered, so that his selection is not only warranted but rational. I may say, however, that in practice the way in which the heat operates upon the medium, the vapor of water for instance, makes differences which cannot be included in so simple an expression. The actual result in such case is really a function of the simpler expression, much as the magnetization is a function of the exciting force. In my investigation I therefore took the actual pressures and volumes derived by experiment as formulated and tabulated in connection with an ideal cylinder of unit capacity, and found the weight of steam required to fill such a cylinder under the conditions assumed. To this was added the weight of steam required to furnish the thermal units for the actual mechanical work performed in such ideal cylinder; next the cost due to cylinder condensation expressed in terms of the weight of steam condensed and a modification of the same due to variation in the relative size of the engines based on the amount of power developed. It will be seen that I considered that the relative power varied the absolute cost as respects this item only, whereas Prof. Carpenter has considered that it affects all the costs according to a certain rule. I next considered the costs, due to loss of pressure and other incidental losses, and finally the saving in cost due to expansion. The summation of these various items gave the total cost. I provided

a separate formula for each one of the several items based necessarily upon experiment or calculation, or both, so that possible errors in any one of the several items could not have as great influence on the final result as if a mere empirical formula were used for the total losses. It is believed, therefore, that my formulæ and the tables calculated there from are from the methods adopted sufficiently accurate to ascertain the probable water consumption beyond present limits of experiment, and predictions were made at the time as to the economy of non-condensing engines for pressures as high as 500 pounds, which may be referred to by those interested in the subject.

An empirical formula is used in the paper of Prof. Carpenter to express the total losses. The formula does not purport to show absolute results, but the variations from a known result due to change of load. By this method an accurate starting point is provided for each particular engine considered, and the results may be applied to all kinds of engines. The comparison with the various experiments on different kinds of engines shows that the increase in cost due to varying the load in either direction, compared with that due to maximum economy is expressed within the limits of observation very satisfactorily by the formulæ.

In this connection I wish to call attention to the large number of valuable experiments which have been made by Professor Carpenter with steam engines of various kinds, and which have added largely to the general information on the subject. While the formulæ in this particular paper should be confined simply to the questions of variations of load, the tabulated results are of great value, independent of this special feature, on account of the large amount of valuable information brought together in condensed form.

PROF. CARPENTER-I am very much indebted, indeed, to Dr. Emery. This paper does not treat directly of the cost of operating or installing an engine, in any way whatever. I never felt competent to deal with that subject, and the remarks regarding the application of this paper to engine costs seems to have resulted from the fact that I have not made a clear statement of the object of this paper. The principal object is merely to express this fact; that the more economical the engine the less it seemed to be affected by the variation of power; and secondly, to give a simple expression showing the water consumption for any class of engine under any condition. I did not have data to go beyond that, and I did not desire it to be understood that the paper meant to give anything more than that. The paper is not intended to be used in computing the required sizes of engines, although I fully appreciate the value of Dr. Emery's remarks regarding its application in that direction. I had supposed that the paper would be useful to electrical engineers principally in pointing out the probable economy of any engine whose rated power was known. I desired also to point out that experiments show that the more economical type of engine was less affected by variations in power than the more wasteful type. That, I thought,

would be the practical application of the results. I believe that the tabulated results-as indeed, Dr. Emery seems to think-on page 319, agree within fairly approximate limits of the actual consumption, say within one or two pounds of water per indicated horse-power per hour, from that obtained in practice.

The paper by Professor George S. Moler on "An Automatic Printing Speed-Counter for Dynamo Shafting," was then read by Dr. Nichols. Dr. Nichols prefaced the reading of the paper with the following remarks:

In the laboratories at Ithaca we have been compelled to use power from a variety of sources-water power, steam power from various engines, and even the two powers combined, and have been subjected thereby to perplexing changes of speed in our shafting. This fact made it desirable to have some means of knowing the range of flunctuation. It was this state of affairs which suggested to Prof. Moler the machine to be described in this paper. The only reason for presenting this account of it here is that the machine having been in operation for some months and having proved very useful to us, it seemed that it might be useful elsewhere.

of the American Institute of Electrical En gineers, New York, May 17, 1893, President Houston in the Chair.

AN AUTOMATIC PRINTING SPEED-COUNTER FOR

DYNAMO SHAFTING.

BY GEO. S. MOLER.

The automatic printing speed-counter was designed and constructed by the writer, to supply a need felt of having a continuous record of the speed of the shafting which drives the dynamos and other apparatus being used by students in their laboratory experiments.

During part of the year the shafting of the dynamo laboratory at Cornell University is driven by water power, the wheels being situated at the bottom of a deep gorge, and several hundred feet distant. The power is transmitted by means of a wire cable running over large grooved sheaves, and the gate hoisting apparatus is operated by a wire rope passing around drums. No automatic regulator has yet been successfully applied to these wheels, so we have to rely upon hand regulation. On account of this, consider. able variations of speed take place, although a tachometer is watched quite closely by the attendant in charge. The variations make it necessary in performing an experiment to continually take account of speed.

The printer (see Fig. 1) is essentially a speed-counter which prints the speed at the end of each minute upon a strip of paper, and does this continuously, requiring very little attention. It was built to give the speed of a shaft which runs at about 140 revolutions per minute, but it has a range of from 30 to 185 per minute.

It is connected to the main shaft of the dynamo laboratory by sprocket-wheels and chains, so that the shaft carrying the worm revolves at exactly the same rate as the main shaft. The

type-wheel is about eight and one half inches in diameter, and is made by clamping printers type between a disk and a ring fastened with screws to one side of it. The disk has a series of small holes drilled in it at equal distances apart, and dowel pins passing through holes drilled in the type, hold the latter in place. If any of the type become worn, or accidentally bruised, the ring can easily be removed and new ones can be inserted. The type are spaced so as to correspond with the number of teeth of the large gear-wheel which engages with the worm. printing is done upon a one-half inch tape of district telegraph paper. A typewriter inking ribbon is employed, and as it is fed along, it shifts sidewise back and forth so that the whole width of the ribbon is used. It takes several weeks to go once the length of the ribbon.

The

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The type wheel practically starts from its zero reading at the beginning of each minute. It is necessary to have it do this, in order that the number printed at the end of the minute shall be the exact number of revolutions for that minute.

When a common speed-counter is used, its index is first set to zero, and it is then applied to the end of the shaft for just one minute, then is withdrawn and read. It is again set to zero, and the operation is repeated, but in doing this, a minute or more is lost each time while setting. Now if the speed were not too great, the index-wheel might be arranged so that it could be

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