Edison: His Life and Inventions

by Frank Lewis Dyer; Thomas Commerford Martin

Here follows HIS explanation, after which he goes on to say: "At this point plausibly comes in a suggestion that the internal part of the circuit be made very small and the external part very large. Why not (say) make the internal part 1 and the external 9, thus saving nine-tenths and losing only one-tenth? Unfortunately, the suggestion is not practical; a fallacy is concealed in it."

He then goes on to prove his case mathematically, to his own satisfaction, following it sadly by condoling with and a warning to Edison: "But about Edison's electric generator! . . . No one capable of making the improvements in the telegraph and telephone, for which we are indebted to Mr. Edison, could be other than an accomplished electrician. His reputation as a scientist, indeed, is smirched by the newspaper exaggerations, and no doubt he will be more careful in future. But there is a danger nearer home, indeed, among his own friends and in his very household.

". . . The writer of page 242" (the original article) "is probably a friend of Mr. Edison, but possibly, alas! a wicked partner. Why does he say such things as these? 'Mr. Edison claims that he realizes 90 per cent. of the power applied to this machine in external work.' . . . Perhaps the writer is a humorist, and had in his mind Colonel Sellers, etc., which he could not keep out of a serious discussion; but such jests are not good.

"Mr. Edison has built a very interesting machine, and he has the opportunity of making a valuable contribution to the electrical arts by furnishing authentic accounts of its capabilities."

The foregoing extracts are unavoidably lengthy, but, viewed in the light of facts, serve to illustrate most clearly that Edison's conceptions and work were far and away ahead of the comprehension of his contemporaries in the art, and that his achievements in the line of efficient dynamo design and construction were indeed truly fundamental and revolutionary in character. Much more of similar nature to the above could be quoted from other articles published elsewhere, but the foregoing will serve as instances generally representing all. In the controversy which appeared in the columns of the Scientific American, Mr. Upton, Edison's mathematician, took up the question on his side, and answered the critics by further elucidations of the principles on which Edison had founded such remarkable and radical improvements in the art. The type of Edison's first dynamo-electric machine, the description of which gave rise to the above controversy, is shown in Fig. 1.

Any account of Edison's work on the dynamo would be incomplete did it omit to relate his conception and construction of the great direct-connected steam-driven generator that was the prototype of the colossal units which are used throughout the world to-day.

In the demonstrating plant installed and operated by him at Menlo Park in 1880 ten dynamos of eight horse-power each were driven by a slow-speed engine through a complicated system of counter-shafting, and, to quote from Mr. Clarke's Historical Review, "it was found that a considerable percentage of the power of the engine was necessarily wasted in friction by this method of driving, and to prevent this waste and thus increase the economy of his system, Mr. Edison conceived the idea of substituting a single large dynamo for the several small dynamos, and directly coupling it with the driving engine, and at the same time preserve the requisite high armature speed by using an engine of the high-speed type. He also expected to realize still further gains in economy from the use of a large dynamo in place of several small machines by a more than correspondingly lower armature resistance, less energy for magnetizing the field, and for other minor reasons. To the same end, he intended to supply steam to the engine under a much higher boiler pressure than was customary in stationary-engine driving at that time."

The construction of the first one of these large machines was commenced late in the year 1880. Early in 1881 it was completed and tested, but some radical defects in armature construction were developed, and it was also demonstrated that a rate of engine speed too high for continuously safe and economical operation had been chosen. The machine was laid aside. An accurate illustration of this machine, as it stood in the engine-room at Menlo Park, is given in Van Nostrand's Engineering Magazine, Vol. XXV, opposite page 439, and a brief description is given on page 450.

With the experience thus gained, Edison began, in the spring of 1881, at the Edison Machine Works, Goerck Street, New York City, the construction of the first successful machine of this type. This was the great machine known as "Jumbo No. 1," which is referred to in the narrative as having been exhibited at the Paris International Electrical Exposition, where it was regarded as the wonder of the electrical world. An intimation of some of the tremendous difficulties encountered in the construction of this machine has already been given in preceding pages, hence we shall not now enlarge on the subject, except to note in passing that the terribly destructive effects of the spark of self-induction and the arcing following it were first manifested in this powerful machine, but were finally overcome by Edison after a strenuous application of his powers to the solution of the problem.

It may be of interest, however, to mention some of its dimensions and electrical characteristics, quoting again from Mr. Clarke: "The field-magnet had eight solid cylindrical cores, 8 inches in diameter and 57 inches long, upon each of which was wound an exciting-coil of 3.2 ohms resistance, consisting of 2184 turns of No. 10 B. W. G. insulated copper wire, disposed in six layers. The laminated iron core of the armature, formed of thin iron disks, was 33 3/4 inches long, and had an internal diameter of 12 1/2 inches, and an external diameter of 26 7/16 inches. It was mounted on a 6-inch shaft. The field-poles were 33 3/4 inches long, and 27 1/2 inches inside diameter The armature winding consisted of 146 copper bars on the face of the core, connected into a closed-coil winding by means of 73 copper disks at each end of the core. The cross-sectional area of each bar was 0.2 square inch their average length was 42.7 inches, and the copper end-disks were 0.065 inch thick. The commutator had 73 sections. The armature resistance was 0.0092 ohm, [28] of which 0.0055 ohm was in the armature bars and 0.0037 ohm in the end-disks." An illustration of the next latest type of this machine is presented in Fig. 2.