was very decisive and complete, the hand-worked seam giving way at 300 pounds pressure, while the machine work remained good.

Previously to this there had been some intervening test regarding the stays, after which the longitudinal stay bolts were removed altogether, and the boiler was tested without them from that time to the end of the trials, so far as they have been carried, and no yielding of the ends has yet occurred.

Before reaching the highest resistance of which the boiler was reckoned capable, another illustration was afforded as to the risk of placing reliance on cast-iron seatings for fittings to steam boilers. When the boiler had been once again restored with all joints doubleriveted by machine, and everything as good as could be, considering the many tests the boiler had gone through, a somewhat unexpected fracture took place in the only remaining external cast-iron seating, viz., that below the boiler at the front end furnished for attaching the blow-off elbow pipe to. At 300 pounds pressure this casting gave way, tearing the shell plate longitudinally, as had been the case in all other such fractures, and straining the lower part of the front plate together with the front internal manhole mouthpiece inwards, and tearing the external angle-iron at the lower part of the boiler.

This had to be repaired, and thus after it had by successive trials been shown that one cast-iron part after another must be discarded, the final burst was attempted, and successfully carried out on the 11th instant, when at 310 pounds pressure a clear longitudinal rent was caused in the central ring of plates, and at the bottom of the boiler, just at the very spot that by all calculation should have been the weakest. Possibly, had the whole boiler been quite new when this last test was applied, and the iron not been subjected to repeated strains closely approaching its limit of strength, the pressure would have reached 320

pounds, or the ultimate calculated strength of the double-riveted joint.. Be this as it may, it has now been demonstrated that this form of Lancashire boiler, fairly made, and of good material, is reliable to the extent that calculation would lead one to expect. These experiments were witnessed from time to time by many gentlemen who take a great interest in such matters and stand foremost amongst the engineers

of England, amongst whom may be mentioned Mr. J. Ramsbottom, Mr. Turnbull, Mr. Inglis, Mr. Scarlett, Mr. Thomas Traill, Chief Inspector of the Board of Trade, also one of the staff of engineers of Engineering. The boiler was made by Mr. Thomas Beeley, of Hyde Junction Iron Works, near Manchester, under the direction of Mr. Lavington E. Fletcher, the Chief Engineer to the Steam Users' Association.

NEW ELECTRIC MOTOR.

By WILLIAM WOODNUTT GRISCOM.

Paper read before the Franklin Institute Nov. 17th, 1880.

An electric motor, as the name indicates, is an engine for converting electricity into mechanical force. This is done most efficiently through the medium of electro-magnetism, and the honor of inaugurating the movement which has led to the utilization of this force as a motive power belongs to our own Professor Henry. His first paper on this subject appeared in 1831. In the following year Salvatore dal Negro constructed his motor and described it in detail. The first electric motors were rude machines, about as efficient as Hero's steam engine, but it hardly took the world more years to perfect the one than it required centuries to complete the other. Dal Negro's motor consisted of a fixed electro-magnet, which, by suitable interruptions of the electric current, alternately attracted and released a lever by which the mechanism was driven.

In 1835 Prof. Jacobi, of St. Petersburg, constructed an electric engine at the expense of the Czar Nicholas, with which, after four years of further experiment, he was able to drive a twelve-oared boat against the swift current of the Neva at the rate of three miles an hour. His enormous battery consisted of sixty-four cells, containing twenty square feet of platinum.

This was in all respects an apparent failure, and the philosopher was thoroughly disheartened while standing unwittingly on the threshold of a brilliant success. In the first place, he attempted the impossible in trying to get a great power economically from any battery, and in the second place no powerful battery had yet been invented. But his engine was an excellent one, and the subsequent inventors failed to equal it until Gramme, of Paris, discovered that one of his own dynamo-electric generators would act in the reverse direction as an admirable motor.

The interval between 1839, when Jacobi's motor was abandoned, and 1870, when Gramme's machines came into notice, was occupied by a large number of inventors, who brought to their work a world of ingenuity, and all the learning of all the sciences save one, but that

one was the only key to success-electro-magnetic induction. In the meanwhile Mr. Joule, himself a former seeker after this nineteenth century philosopher's stone, dashed the hopes of his co-inventors by his demonstration of the Conservation of Energy. This magnificent work, the grandest perhaps in the history of science, was immediately made the basis of a series of experiments, which it would be out of place to detail here. Suffice that Mr. Joule proved to the satisfaction. of all scientific minds that the mechanical energy of the electrical current, produced by the consumption of one pound of zinc in a Daniell's cell, is equal to 1,106,160 pounds raised to the height of onefoot; in a Grove's cell, which has 13 times the electro-motive force of Daniell's, to 1,843,600 pounds raised to the height of one foot, or, in the sulpho-chromic acid battery now before you, which has double the electro-motive force of a Daniell's, 2,212,320 pounds. raised to the height of one foot. Dr. Scoresby and Mr. Joule statetheir conclusions in the following sentence: "Upon the whole we feel ourselves justified in fixing the maximum available duty of an electromagnetic engine, worked by a Daniell's battery, at 80 pounds, raised one foot high for each grain of zinc consumed." This is about half the theoretical duty. In a Grove battery the same proportion would give 144 pounds, and in the sulpho-chromic battery 160 pounds, raised one foot high for each grain of zinc consumed. This result was immediately compared with the duty of the best type of steam engine per grain of coal, and it was found that one grain of coal lifted 143 pounds one foot high. But zinc, at the most favorable computation, costs ten times as much as coal, and the force it yields is, therefore, as 143 is to 160, or about nine times as costly.

The conclusion instantly drawn by the scientific world was that electricity produced by the consumption of zinc can never compete with steam, but it is the purpose of this paper to collect certain factswhich will show that this conclusion is erroneous.

History is teeming with instances where noted scientific men declared that there was nothing attainable beyond their immediate vision, and proved with sarcastic argument and brilliant syllogism that further advance in certain directions was impossible. So it was with the steamship. An eminent scholar and mathematician, some fifty years ago, proved beyond the peradventure of a doubt that an ocean steamship was an absurd dream. His calculations showed that one could not be built large enough to carry her own coal across the Atlantic.

And so these gentlemen, having proved that electricity produced by zine is nine times as costly a source of power as steam produced by coal, predict that electric motors can never usefully compete with steam engines. Now, man-power, according to the tables of a wellknown English engineer, is one hundred times as costly as steam; nevertheless there are several circumstances in which we prefer men. It is certain that we would never employ men if we could get a steam engine to do the work more cheaply, and it is equally certain that we would not use electricity where steam was applicable. But steam is not applicable, for reasons which will be given later in detail, to work in which we require a small amount of power in constant readiness for action. In these cases-such as jewelers' lathes, dental engines and the various tools of small machine shops, which employ but a small force of men-we have never been able to find a source of power adapted to the work which, if not as cheap in proportion as large steam engines, should yet be more economical than human energy. The fact is that whereas, according to Joule, the best electric motors are nine times as costly as steam power, human energy is eleven times as costly as electricity. And, inasmuch as human energy, which is one hundred times as costly as steam, is frequently preferred to steam engines, a fortiori electricity will often be preferred to steam; and it will require no argument to show that the human energy thus saved from exhaustion in the exercise of brute force can be devoted to a higher use.

By way of illustration, the application of human energy to the sewing machine is not only a false economy, but has proved the cause of many new and painful diseases in female operators, which embitter their lives and affect the physique of their offspring. If any motor can be substituted for human energy in this field, there can be no greater or more convincing consideration offered to invite attention. to it.

The sewing machine is in almost every house, and the seeds of these diseases are spread in every class of society. The remedy, as before mentioned, is a household motor, and it was natural to suggest a small steam engine for this purpose; but steam is unsuited to this end, because

1st. It requires time and trouble to start it to work, and a busy housekeeper, who may only need, perhaps, to do five minutes of sewing, has no time to waste.