made fast to the lower end of the rocker itself, but to the upper and lower ends of a link made to slide up and down on a pivot placed at the bottom of the rocker. This link is raised or lowered by means of the reverse-lever in the cab. When it is lowered, only the forwardmotion eccentric influences the cylindervalve and when it is raised the backward-motion eccentric alone is operative. Whichever end of the link is left free from the pin at the end of the rocker simply runs free without effect upon the cylinder valve.

By raising part way the link which governs the rocker, the engineer accomplishes what he terms shortening the stroke," when the engine is to run at high speed. This is done to economize steam for it makes the valve-stroke shorter and so opens the ports for shorter periods. Less steam is thus admitted to the cylinders and, of course, it exerts full pressure on the piston only at the beginning of the stroke, its pressure diminishing as the piston recedes

before it but being sufficient to sustain the speed gained.

A diagram is printed herewith in which the various parts of the locomotive mentioned above are indicated. A slight study of the drawing will probably be necessary to a perfect understanding of the description.

It should be said that every ordinary locomotive is, in reality, two engines, one on each side of the machine. They are so arranged that they do not act upon the driving-wheels simultaneously, however, but when the crank on one side is at the extremity of the stroke, that on the other side is on the quarter, either immediately above or below the axle, so that power will be exerted by one or other engine at all times and so that the two cannot, by any possibility, be stopped "on the dead center," or exactly at the ends of their stroke, when the cranks are opposite the axle. If the engine was built so that this could occur, there would be times when it could not be started from the position described without application of outside force.

Meaning of Trainsmen's Code What is the meaning of the hand signals used by trainmen?-Traveler.

A flag or lamp swung across the tracks, a hat or any object waved violently by any person on the tracks, signifies danger and is a signal to stop. The hand or lamp raised and lowered vertically is the signal to move, as in a. The hand or lamp swung across the track is a signal to stop, as in b. The hand or lamp swung vertically in a circle across the track when the train is standing is the signal to move back, as in c. The hand or lamp swung vertically in a circle at arm's length across the track when the train is running is the signal that the train has parted, as in d.

Producer-Gas Plant Regulations What are the regulations of the National Board of Underwriters concerning producergas plants?-H. L. B.

Pressure Systems. All pressure systems must be located in a special build

ing or buildings approved for the purpose and at such distance from other buildings as not to constitute an exposure thereto.

2. Suction Systems.-(a) A suction gas-producer of approved make, having a maximum capacity not exceeding 250 horse-power, may be located inside the building, provided the apparatus for producing and preparing the gas is installed in a separate, enclosed, well ventilated, fire-proof room, with standard doors at all communicating openings.

The installation of gas-producers in cellars, basements, or any other place where artificial light will be necessary for their operation, is considered hazardous, and will not be permitted except by special permission of the underwriters. having jurisdiction.

(b) The smoke and vent-pipe shall, where practicable, be carried above the roof of the building in which the apparatus is contained, and adjoining buildings, and when buildings are too high to make this practicable, the pipe shall end at least ten feet from any wall. Such smoke or ventpipes shall not pass through floors, roofs, or partitions, nor shall they, under any circumstances, be entered into chimneys or flues.

b

SIGNALS USED BY TRAINMEN.

(c) The platforms used in connection with generators must be of metal. Metal cans must be used for ashes.

(d) The producer and apparatus connected therewith shall be safely set on a solidly built foundation of brick, stone,

or cement.

(e) While the plant is not in operation the connection between the generator and scrubber must be closed, and the connection between the producer and ventpipe opened, so that the products of combustion can be carried into the open air. This must be accomplished by means of a mechanical arrangement which will prevent one operation without the other.

(f) The producer must have sufficient mechanical strength successfully to resist all strains to which it will be subject in practice.

(g) Wire gauze, not larger than sixty mesh or its equivalent, must be used in the test-pipe outlet in the engine-room.

(h) If illuminating or other pressure gas is used as an alternative supply, the connections must be so arranged as to make the mixing of the two gases, or the use of both at the same time, impossible.

(i) Before making repairs which involve opening the gas passages to the air, the producer-fire must be drawn and quenched, and all combustible gas blown out of the apparatus through the ventpipe.

(j) The opening for admitting fuel shall be provided with some charging device so that no considerable quantity of air can be admitted while charging.

(k) The apparatus must have nameplate giving the name of the device, capacity, and name of maker.

Why Electric Lamp Will Not Work Kindly tell me why 110 volt lamps will not work with the wiring shown in the enclosed sketch. Half of them light when the switch is thrown as shown. I should think that by throwing the switch the other way, they would all burn with one-half the candle power, but they do not even glow.-B. R.

How LAMPS THAT WILL NOT Work are WIRED.

These lights are wired so that the upper lights are in parallel when the switch is thrown up, and the two lights in series across 110 volts when the switch is thrown down. Thus in the first case, you will get 110 volts across each lamp and it will give it full candle power. In the second case the

lamps will give only 55 volts. It is a mistake to suppose that the lamps will give one-half of their light on one-half voltage, because below about 90 volts, they give no light.

A dia

both terminals from the circuit. gram of the necessary connections and wiring of a compound-wound dynamo is shown in the figure. The leads from the external circuit are first connected to the fuses, F, in order to protect the dynamo from large or dangerous currents. If a current greater than a safe one for the dynamo passes through these fuses they melt and so break the circuit. From the fuses leads connect with the main switch, S, and from this to the brushes through the series coils. The rheostat, R, is connected in series with the shunt coils for the purpose of regulating the field. strength and hence the voltage of the machine. By moving the arm of the rheostat, the current in the field coils is varied.

To Measure Draft in Chimney How can you measure the draft in a chimney? We are using natural draft.-N. A. F.

The draft in a chimney is caused by the difference in weight between the hot gases inside and the air outside. The force, or intensity of the draft is equal to the difference of these weights, and is measured by a draft gauge. One form of the instrument is a tube bent in the form of the letter U. The tube is partially filled with water, one leg being

connected to the interior of the chimney and the other open to the external air. The difference of the water levels in the two legs indicates the difference of pressure and the amount of draft.

On account of the slight movement of the fluid and the error caused by the water being attracted to the dry tube, the differential draft gauge is used. The form is shown by the accompanying figure. The fluid used is a special non-drying and non-evaporating oil of known specific gravity. The incline and diameter of the tube are so proportioned that the reading represents distilled water in hundredths of an inch. The instrument is capable of measuring two inches of water pressure.

Boiler Problems

1. How can I tell what size boiler to select for house heating?-T. H. F.

1. It is advisable always to check the catalogue ratings of boilers, when selecting one for a given service, as follows:

Suppose the direct radiating surface, including piping, is 3,000 square feet. One square foot, it may be assumed, will give off about 250 heat units in one hour

-a heat unit being the amount of heat necessary to raise the temperature of one pound of water, 1 degree Fahrenheit. A pound of coal may safely be counted on to give off to the water in the boiler 8,000 heat units. Now, 3,000 square feet times 250 heat units divided by 8,000 heat units, gives the amount of coal burned per hour; and this, divided by the square feet of grate, gives the rate of combustion per square foot per hour. Suppose in this case, the grate has an area of fifteen square feet;

HE craving of humanity for retarding the advent of senility and thus prolonging life is embodied in the popular myth of the Fountain of Youth. Similar ideas have been more recently discussed by the partisans of what is called "Simple Life," according to whose opinion the natural lifetime of man, like that of certain related mammalia, would correspond to the 5 or 6fold time required for the conclusion of growth, that is, would be about 100 to 120 years, and according to whose doctrines humanity, by adapting life to the laws of nature, would be at liberty to pre

vent a premature death. The same problem has finally been dealt with of late years by scientists, such as Metschnikoff, according to whose opinion senility is nothing else but a disease accessible to medical treatment. Neither the simple life theories nor the investigations of medical science have however, so far succeeded in suggesting any method of actually prolonging life.

The phenomena characteristic of old. age, and which manifesting themselves by all kinds of trouble, after a slow decay, result in the final dissolution of life, as is well known, are due to an increasing rigidity of the arteries. These phenomena called arteriosclerosis, so far from attending exclusively old age, un