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Inventor of the System of Wireless Telegraphy that bears his name

creation of much more powerful voltage in order to bring about the required results.

The third and last question arises: How can these ether vibrations be detected? The original method, and the one in use at the present time by most

INSTRUMENT ROOM, HOLYHEAD STATION.

systems of wireless telegraphy, is by means of a coherer. A brief description of the principle underlying this will help us to understand its working. If we were to take some soft iron filings and place them in a vial around which was wound an ordinary copper wire that could be connected in the circuit of an electric battery, we should find that the iron filings would be irregularly distributed until we passed a small electric current through the wire surrounding the vial. Then they would, through magnetic force, all arrange themselves in a parallel direction and would remain so until the current was cut off and the vial mechanically disturbed. A similar effect, only much lighter, takes place from the impact of a Marconi ether wave. It has also been found that a mechanical mixture of silver and nickel filings with mercury is much more sensitive to the impact of a wave than iron, and these are now used in a small glass tube. Taken together this is technically known as the "coherer."

This coherer is then placed in the circuit of an ordinary electric door-bell circuit, or in that of a Morse instrument, and its connecting wires penetrate the filings just far enough so that the current of electricity cannot operate the Bell or Morse instrument owing to the resistance of the irregular air spaces in the filings.

If the impact of an ether wave be then received, it will affect the filings sufficiently to render them more or less parallel, break down the resistance of the irregular air spaces, and operate the bell or key, thus giving a dot or dash signal as required. A second small battery is arranged so as to de-cohere automatically the filings after each dot or dash.

Comparatively recently, Marconi invented what has been called his magnetic detector. This acts on a different principle. A coil of soft iron wire is made by mechanical means to pass near the poles of a fixed magnet. This has the effect of magnetizing and demagnetizing the wire while passing the different magnetic poles. The demagnetization, however, is incomplete, a condition known as hysteresis remaining. This completely and rapidly disappears when subject to the impact of a Marconi wave, resulting in a sound or click readily detected by an ordinary telephone-receiver attachment. This method is now adopted for all long-distance work. It is very simple in character, and admits of much greater

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which are exactly tuned or syntonized to the transmitter, this being to a certain degree necessary in order to protect the secrecy of the message. We know what tuning is in connection with vibrations in air. If we take two tuning forks of precisely the same key, placing them some distance apart in a room, then start one vibrating, the other will take up the same tone, continuing it for some time. If, however, the instruments are of different keys, or, in other words, are not tuned to each other, the second one will remain unaffected.

A similar condition of things exists in connection with ether vibrations. Owing however, to their enormous frequency, the tuning possibilities are very much greater. Marconi has, by a simple contrivance, been able to accomplish this. By this tuning arrangement, he can in the same room receive, without confusing

messages sent from the same or different places, as was admirably demonstrated in England before Professor Fleming, when he succeeded in taking messages in English and French simultaneously on superimposed instruments.

The above narration is intended not as a scientific treatise, but a simple statement of the principles involved. Marconi, though young, has already accomplished much. The bridging of the Atlantic by etheric signals, though Utopian but a short time ago, has been successfully accomplished; and a new force, hitherto unknown, has sprung into existence. It will find its place in the onward march of civilization and commerce, as have the telegraph, the cable, and the telephone; reaping its share of commercial reward as did they, and all through the remarkable prescience and genius of one man, Marconi.

The only buildings in the world which are earthquake-proof are the Japanese pagodas. There are many which are 700 or 800 years old and as solid as when first built. The reason lies in their construction. A pagoda is practically a framework of heavy timbers which starts from a wide base and is in itself a substantial structure, but is rendered still more stable by a peculiar device. Inside the framework and suspended from the apex is a long, heavy beam of timber, two feet thick or more. This hangs from one end of the four sides. Four more heavy timbers, and, if the pagoda be very lofty, still more timbers are added to these. The whole forms an enormous pendulum, which reaches within six inches of the ground. When the shock of an earthquake rocks the pagoda, the pendulum swings in unison and keeps the center of gravity always at the base of the framework. Consequently the equilibrium is never disturbed.

The latest type of British submarine boat, built by Messrs. Vickers Sons & Maxim, has attracted much attention in naval circles. It has a speed under water of between nine and ten knots. It is a modified development of the Holland type, the length of the new boat being 150 feet and 120 feet in the original. The radius of action in the new type is 500 miles; and in the Holland, about 300 miles.

The weight is too great to permit the boats to be carried on shipboard. In practice evolutions, the submergence usually lasts three hours, but the quarters are very cramped and the crew is obliged to keep fixed stations, as the displacement of the center of gravity might cause the boat to take a disastrously deep plunge. It has been suggested that three sets of these boats should be provided, each of which would have three days on duty and six days off, in order to preserve the health of the crew.

EXHAUST

STEAM HEATING

by C.L.HUBBAR

ARD

T

HE rapid increase in the number of isolated lighting plants invests with a greater than usual importance the question of the proper utilization of exhaust steam. In general, we may say that it is a matter of economy to use this for heating purposes, although various factors must be considered in each case to determine to what extent this is true. The more important considerations bearing upon the subject are:-the relative quantities of steam required for power and for heating, the length of the heating season, the type of engine used, the pressure carried, and, finally, the question whether the plant under consideration is entirely new or whether, on the other hand, it involves the adapting of an old heating system to a new plant.

The first use to be made of the exhaust steam should be the heating of the feedwater, as this effects a constant saving both summer and winter, and it can be done without materially increasing the back pressure on the engine. In ordinary practice, only about one-fifth to one-fourth of the exhaust steam can be used in heating the feed-water from a temperature of 40° up to 210°. This is easily shown as follows:

We may assume, under ordinary conditions, that about 80 per cent of the steam supplied to an engine is discharged from the engine in the form of steam at low pressure, the remaining 20 per cent being lost through condensation, etc. The latent heat of a pound of steam at 2 pounds gage pressure is 960; therefore,

out of each pound of live steam furnished to the engine, there will be 960X.8=768 heat units available for heating purposes. It requires practically 210-40=170 heat units to raise one pound of feed-water from 40° to 210°; and 49, or between one-fifth and one-fourth. Taking the larger figure, we have left, for heating or other purposes, .75X.8=.6 of the entire quantity of steam supplied to the engine. The principal objection to the use of exhaust steam for heating has been the higher back pressure required

F

E

B

FIG. 1.

on the engine. The loss in power of an engine from back pressure is nearly proportional to the ratio of the back pressure to the mean effective pressure. This is shown graphically in Fig. 1.

Let the work done by one stroke of the engine be represented by the area A B C D E. If the rectangle F G DE be drawn, having an equal length and the same area, then the mean effective pressure will be represented by the height E F. Let E D be the normal back pressure line; then if it be raised to the position I J, the resulting lost work will be given by the area I J D E. As the

rectangles F G DE and IJD E have the same length, their areas are as their heights, which represent the mean effective and back pressures respectively. From this it is evident that any increase in the back pressure cuts down the power in proportion to the ratio of the increase in back pressure to the mean effective pressure.

Example. The M. E. P. of an engine is 40 pounds and the back pressure is raised 5 pounds; what will be the loss in power? Five-fortieths=%, or 12.5 per cent, loss in power.

There are two ways of offsetting this loss. One is by raising the initial or boiler pressure, and the other is by increasing the cut-off of the engine. The first method is illustrated graphically in Fig. 2.

Let A B C D E be the indicator diagram of an engine exhausting against atmospheric pressure. If the back pressure line is raised to the position I J, the lost work per stroke will be represented by the area I J DE; and, to offset this, the line of initial pressure must be raised to such a height that the area A KLM C B will equal the area I J D E. The required increase in boiler pressure for offsetting the effect of a higher back pressure may be found approximately by the use of the following table:

MEAN PRESSURE RATIOS

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cent.

It is desired to use the exhaust steam for heating, at a pressure of 5 pounds per square inch. How much must the boiler pressure be raised in order that the engine may have the same power at the same cut-off?

It is evident that if the power of the engine is to be kept the same, the mean effective pressure must remain constant. The normal back pressure on an engine exhausting into the atmosphere is about 2 pounds gage. Referring to the above. table, we find the ratio for 4 cut-off and 5 per cent clearance to be .62, from which the mean pressure in the above case is (80+15)X.62=50 pounds, and the mean effective pressure is 59-17-42 pounds. K--

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If the back pressure is to be raised to 5 pounds gage, or 20 pounds absolute, the mean pressure must also be increased 3 pounds in order to keep the mean effective pressure the same. This calls for a mean pressure of 62 pounds absolute; and, dividing this by .62 (the ratio for 1/4 cut-off and 5 per cent clearance), we have an initial pressure of = 100. pounds called for, instead of 95 as in the first case. This shows that under the conditions of the problem an increase of 3 pounds in back pressure requires a corresponding rise of 5 pounds in the boiler pressure to keep the power of the engine. the same with a constant cut-off.

The effect of the second method (that is, increasing the cut-off) is shown in Fig. 3, in which the added area B K L C must equal IJDE. The necessary increase in the cut-off for any given case can also be found by the use of the table already given.

Example. An engine cutting off at 1/ stroke is supplied with steam at ΙΟΟ pounds gage pressure. Clearance of the

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