a vacuum under a piston. Although having pressure on his "digester," it does not seem to have occurred to him to make use of steam otherwise than to fill a cylinder under a piston as a means of obtaining a vacuum by condensation. Papin constructed a vacuum engine as follows: He took a tube two and one-half inches in diameter and fitted therein a piston with a square piston rod through top head. When piston and rod were at the top of the cylinder a notch in the piston rod just cleared above the top head and was locked there by a small iron rod swinging on a circle and which was held in place by a spring. There was a small vent hole drilled through piston head. A small rod was put through top cylinder to plug the small hole in piston. The thing was made to work by putting a small amount of water in the cylinder and piston forced down upon it until some of the water came through the vent, after which the vent hole was stopped up with the small rod. Fire was then started under the cylinder. After a certain pressure was created the piston was forced to top of cylinder and was held there by the rod being forced into piston handle by spring. The fire was at once removed and as the steam condensed the vacuum was created. Atmospheric pressure on top of piston caused it to descend with great energy, when the supporting handle was pulled out of the notch in the piston rod. This little engine would force aloft 60 pounds as quickly as the atmospheric pressure would force piston to the bottom of the cylinder, yet the tube itself scarcely weighed five

ounces.

Papin goes on to suggest many uses for this power, but curiously enough, as before mentioned, does not seem to have appeciated the use of the expansive force of steam, but only contemplates its use as the means of forming a vacuum. He must have created pressure of about 12 pounds per square inch in his two and one-half inch cylinder to have raised a weight of 60 younds.

Captain Thomas Savery is given the credit of being the first man who actually

employed steam generated in a boiler for the purpose of doing useful work.

On June 14, 1699, Savery exhibited and worked a small model of his engine at a meeting of the Royal Society held at Gresham College.

In 1702 Savery published a small pamphlet entitled, "The Miner's Friend, or an Engine to Raise Water by Fire." This pamphlet was written very intelligently, the original work being now very scarce, as well as a reprint of the same which came out in 1827. Savery used two boilers placed side by side in brick work. One of these he named the "Great Boiler" and from this he took the steam for his engine. The other boiler was used to supply the great boiler with hot water. When he desired to fill the great boiler he simply created a greater pressure on the small boiler than was carried on the larger one, there being pipe connections with the stop-cock. When pressure was high enough on the small boiler the cock was opened and water was forced into the larger boiler.

Savery's engine has often been described and is well known, and the principle has been made use of in late years in the "pulsometer," a well-known and useful machine for raising water. In describing his engine Savery said, "When a vacuum is formed by the condensation of the steam, the external pressure of the atmosphere, or what is commonly known as suction, will quickly refill the vessel." The boilers used by Savery seem to have been vertical copper cylinders with domed tops from 2 feet to 2 feet 6 inches in diameter and 2 feet 6 inches to 3 feet high. He must have used pressures up to 45 pounds per square inch; consequently, his boilers must have been fairly strong.

Savery was handicapped by the lack of skill and awkwardness of his employees. He seemed possessed of a clear understanding of what he was doing and carefully thought out his methods. Others who had worked with steam before him had not gotten beyond the experimental stage and were contented with raising perhaps a piston by heating

water below it, but Savery separated the boiler, or steam generator, from the engine and thus paved the way for those that followed. Newcomen, who advanced the new source of power to a more useful and advanced stage, owed much to Savery. Savery's engines were shortlived for obvious reasons and soon gave way to the better class brought out by Newcomen.

Of Newcomen but little is known. He was considered a man of great ingenuity. It appears that he had been experimenting privately with a friend who was a glazier and plumber of the same town. The exact line of his experiments are unknown, but believed to have been along lines which led him to use steam for the purpose of obtaining a vacuum under a piston. It is certain, however, that Newcomen, in conjunction with his friend, produced a thoroughly useful combination of engine and boiler, such that it was capable of drawing water from the deepest mines withou depending directly upon the pressure of the steam. The superiority of Newcomen's engine soon asserted itself and a great many were made and erected to pump water from the mines. In Savery's engine the height that water could be raised was limited by the steam pressure, while in Newcomen's engine the pressure of the steam had no direct ratio to the height to which water could be raised.

Boilermaking, as has been said, was very crude in Savery's time, hence the trouble he had with his high pressures and it was greatly owing to this cause that so few of his engines came into use. On the other hand, Newcomen only required a pressure slightly above that of the atmosphere, and had no difficulty getting boilers made to stand such pressure. In some of Newcomen's early boilers the lower part was of copper, the upper part of lead.

The discoveries of Papin, Savery and Newcomen foreshadowed great possibilities in the use of steam. The substantial work by the two last named of the trio was principally, if not entirely, in one direction-that of raising water from

mines and thus they were instrumental in the reclaiming of much valuable property. Savery showed that steam could be used for raising the water, but I did not meet with much success. Newcomen by introducing the beam engine with the working cylinder at one end and the pump at the other, was very successful and some of his engines are still doing duty. Newcomen's engines led to the suggestion that they might be used for other than pumping purposes. These suggestions were many and various; among the more definite it was that of propelling ships against wind and tide.

John Payne, 1740-1741, endeavored to raise steam by spraying water on hot metal. Attempts have since been made in the same direction, but without success until quite recently, or since the flash boilers for motor cars came into use. Payne was quite ingenious and made improvements in boilers and advanced some excellent ideas.

John Smeaton, 1740-1747, was a natural mechanic and made large strides in boiler improvements. He erected several large engines of the Newcomen type. The boilers built for these engines were the largest then known. They were 15 feet in diameter at the largest place and 12 feet in diameter at the bottom and stood about 15 feet high. They were made of iron plates riveted together and were set in bricks like brewing coppers. The actual details of construction of these boilers are, unfortunately, not given in Smeaton's reports. Steam boilers before Smeaton's time were globular, or segments of spheres, heat being applied externally. Smeaton introduced flue boilers. He devised the horizontal cylindrical boiler traversed by a flue. Smeaton was the first to design a boiler with an internal firebox.

The first atmospheric engines erected in America were one in New England in 1760 and another about the same date in New Jersey. These were both, it is stated, made in England. About the same time, or later, two engines were erected in New York-one for pumping, the other for sawing. The latter is said

to have been a double acting engine by Boulton and Watt, and was supplied by two boilers-one of wood, the other of plate iron. A wooden boiler was in service in Philadelphia some years later. This boiler was used at the Center Square waterworks from 1801 until 1815, probably at a pressure of two and onehalf pounds or less per square inch. To the present day mechanic there may a doubt arise as to there ever being such a thing as a boiler made of wood. A description of the wood boiler will be given in the March JOURNAL.

Electrical Railroading.

BY ELWOOD GRISSINGER.

PART XIV.

The lead given to the armature conductors when connecting to a commutator to suit certain types of windings must not be confused with the lead given to the brushes with respect to the neutral position of an armature winding in its magnetic field. Three diagrams will aid in describing the lead given to brushes. These diagrams are here referred to as Figs. 1, 2 and 3. The first, or Fig. 1, represents a simple two-pole magnetic field without any armature therein. This figure shows by its dotted lines the path and direction of the lines of force passing from the N to the S pole. It is seen that they pass in straight lines. There is nothing to change their direction from a straight path. As a matter of fact, how

ever, a greater number of lines pass between the adjacent pole tips than through the center for the reason that the distance through the air is much shorter. If the pole faces were plane faces instead of concave, then the magnetic field would be uniform across the entire pole face. An air gap offers a tremendous resistance to the passage of magnetic lines of force. Wherever the air gap is less, a greater number of magnetic lines will pass at that point. The resistance offered to the passage of magnetic lines is termed reluctance.

If an armature core is inserted in the above magnetic field, the result will be similar to that shown in Fig. 2. It is here seen that the lines of force no longer travel in a straight line from pole to pole but that they curve upward and downward as they pass through the armature core from one pole to the other. The degree of curvature will depend entirely upon the dimensions of any air gap that may exist between the armature core and its shaft. Even if there were no actually visible air gap between the core and shaft, still the mere fact that the shaft and core are not an integral mass but separate structures, introduces a joint and this will offer reluctance. Therefore in all equipment through which lines of force are caused to pass, the aim is to have as nearly an unbroken path as possible. The more breaks there are the greater will be the reluctance, and consequently the efficiency of the apparatus is lessened. It is

N

S

N

S

surprising how many lines of force are lost at every such joint. Greater exciting currents must be employed to overcome such losses.

Thus far the lines are shown approximately as they travel through the iron alone. Fig. 3 is intended to give an idea of what happens to the lines when a current is passing through the armature coils. It will be recalled that the armature current as it circulates through the turns of wire wound in the slots also creates a magnetic field in the armature. When this occurs, the armature magnetic field distorts the main field and causes it to bunch up somewhat. This is called distortion. It is also termed armature reaction. The amount or degree of this distortion depends altogether upon the load upon the dynamo or motor, other things being

equal; or what amounts to the same thing, it depends upon the magnitude of the current flowing in the armature. The stronger the armature current the stronger will be the armature field of force, and of course the greater will be the effect of the armature reaction.

A clearer conception of the lead which must be given to the brushes to overcome sparking due to a distorted field can best be obtained by reference to Fig. 4, which is a reproduction of the simplest form of a dynamo or motor. It is assumed in this case that the magnetic field is uniform. A single armature coil is shown as a rectangular loop. Its position with respect to the field of force is vertical. In this position it is embracing the maximum number of lines and cutting none. It is in this position that the direction of the

induced current in the loop will change. This position is called the neutral position of the coil. Sparkless commutation is obtained with such a loop in a working armature by having the brushes so set that when the coil comes into a neutral position the brush will make contact with the commutator segment attached to such loop. As the loop moves away from the vertical position, however, a current is induced in it, passing through the brush into the external circuit in the case of a generator; a current being passed into the loop through the brush in the case of a motor. If, however, the same loop is placed in the distorted field shown in Fig. 3, it is seen that to get the coil into the

condition. In early forms of machines (and now and then modern ones too) the neutral points of armature windings are so narrow that some sparking is evident at the brushes because of the changing direction of currents in the armature coils as they are passing through the neutral zone. The exercise of proper care in design coupled with the use of good material in the field poles and armature core, will give a sufficiently wide neutral zone so that when the brushes are so set that they will show no sparking at light loads, the same condition will be maintained as the heavier currents are passed through the armature. In addition the wider the neutral zone, the more flexible

N

S

neutral position where it is embracing the maximum number of lines the coil will not be in a vertical position with respect to a horizontal line through the poles of the two-pole field shown, but that it must be turned to the right in the case shown. The coils on the armature are fixed in position, however, and the brushes instead must be moved. This gives the brushes their lead. Such a lead is given to the brushes so that all the coils when they reach the neutral position will be connected with the commutator segments then in contact with the brushes. In this way theoretical sparkless commutation is secured.

the field will be and the more readily it will adjust itself for sudden or excessive demands upon the equipment. A sensitive field very quickly and sometimes very forcibly asserts itself by very excessive flashing at the brushes. Sometimes, under very severe conditions, such flashing will be so pronounced as to extend over the commutator from one set of brushes to another and of sufficient intensity to open the main circuit breaker or slow down the engine driving a generator. Such flashing has been termed bucking and is equivalent to a short circuit.