The Thompson-Houston System of Electric Lighting

by H. T. Cory

But however true the foregoing may be, the greatest present use of electricity is to start and maintain light. There are several so-called systems, embracing dynamos, lamps, regulators, etc, from which I select the Thomson-Houston as the one for the purpose of describing for several reasons, first, it is at least as good as the average system of which there is a mushroom growth; second, valuble information was kindly offered by the parent Company; third, a good plant is near to which free acess was given, and fourth, we have at the Mechanical Hall of this University, a dynamo, loaned by the parent Company, which affords information without any inconvenience. As each part of the system comes up to be described a little of its history will be given. As the first part of a system necessary to be produced is the current generator we will first describe

The Thomson-Houston Dynamo.

In considering the current generator the first thing to be decided upon is the definition of the term dynamo. The following is thought to be a correct definition,—A dynamo or dynamo electric machine is a machine which is used to convert energy in the form of mechanical motion into energy of electric currents, or vica-versa. Those used to generate currents of electricity are called dynamos, those used to generate mechanical motion are known as motors.

In attempting to make clear the theory of the dynamo, we will recall some simple experiments. In Fig. 1, send a current around B from right to left. Now A being free to move vertically either up or down, connect its binding posts to a galvanometer (that is, an instrument used to tell the direction of a current and also used to test the relative strength of two or more currents) and move A up suddenly when a current will be generated in A whose direction will be the same as that of the current in B. Now this current is not created energy, because in lifting[^[2]] the coil A, work is expending against the attraction between the coils, as between two currents flowing in the same direction there is an attraction. If we pursue this experiment in its various forms we will find the following statement known as Lentz law is true, viz: “If the relative positions of two conductors A and B be changed of which B is traversed by a current, a current is induced in A in such a direction that by its electro dynamic action on the current in B it would have imparted to the conductor a motion of the contrary kind to that by which the inducing action was produced.”

The theory of this law is that around every wire carrying a current there is a magnetic whirl (Fig. 3). Now if the conducting wire be passed through a hole in a horizontal plate of glass and iron filings be sifted upon the latter they will arrange themselves, as shown in Fig. 2., along lines, radial in this case, known as lines of force, which arranging is due to the magnetic attraction of the current in the wire upon the iron filings. Now in B. Fig. 1, every portion of the wire has just such a whirl and just such lines of force, or magnetic field, and when A is moved each part of the wire of A cuts one or more lines of force of the many magnetic fields making up the magnetic field of the entire coil B. Now when the wire of coil A cuts magnetic field of B a current is generated in A acording to the following statement known as Faraday’s Law; “When a conductor in a field of force moves in any way so as to cut the lines of force there is an electromotive force produced in the conductor in such a direction that supposing a figure swimming in the conductor to turn to look along the positive direction of the lines of force (in Fig. 1, toward axis of B), and the conductor be moved to his right, he will be swimming with the current so induced.” Hence in Fig. 1, the current generated in it will be from left to right.

Practically Faraday’s principle means just this: by moving a wire across a space where there are magnetic lines, the motion of the wire as it cuts the magnetic lines sets up around the cutting wire a magnetic whirl or in other words sets up a current in that wire.

The foregoing laws are the “principles of the dynamo,” yet after their deduction, the progress of the evolution of the dynamo was slow and attended by many dificulties. Between 1860 and 1870 however, a working knowledge of these laws became the property of thousands of mechanics, and by comparing the number of inventions before and after that date (1860) the present generous growth of systems, dynamos and lamps, prove that inventions were almost in proportion to the number of people who had any electrical knowledge. In 1866 Wilde produced a toy magneto-electric machine for giving shocks, in which he used excited electromagnets. In the same years Varley and others produced a machine which excited its own field magnets the type of all machines used in practice. With this principle of Varley’s and Pacinnotti’s ring, Gramme produced in 1871 his since famous continuous current generator, one of which the second dynamo electric machine ever brought to this country can now be seen at the engine house at Purdue University. In 1877 Silas Brush brought out his famous dynamo and it may be interesting to know that he designed and had one made without experimenting in the least. In the following year a patent was issued to Messrs. Elihu Thomson and Edwin J. Houston, Professors of electricity in Philadelphia on the present though much improved Thomson Houston Dynamo.

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Fig. 7.

To go back to Lentz and Faraday’s laws and carefully consider them we can but assent to S. P. Thompson’s “fifteen propositions on the dynamo” which are:—1. A part of the energy of an electric current exists in the form of a magnetic whirl surrounding the wire.