fully adequate street lighting for light traffic. Thoroughfares must have more light because they carry much more traffic than the typical residence street. Business districts must be still better lighted and they are the first part of the city to deserve ornamenal treatment.

For thoroughfares and business districts the asymmetric street. lighting units at present available use either the Bi-lux refractor or the Asymmetric Dome Refractor. Fig. 11 illustrates the Bi-lux refractor. Fig. 12 shows the characteristic distribution which it gives, looking down from directly above. Fig. 13 is the Asymmetric Dome refractor and Fig. 14 shows its characteristic distribution looking down from directly above.

The Bi-lux and Asymmetric Dome Refractors are used inside of ornamental globes or lanterns made of glass, which diffuses the light only slightly. Complete diffusion such as obtained with white glass would destroy the effective distribution obtained from the refractor. A slight degree of diffusion gives an excellent appearance and allows the refractor to perform its function efficiently. An unlimited variety of ornamental designs may be made using the same internal refractor.

It may be thought that the asymmetric idea will reduce street lighting costs. Such is not the case, however. Almost without exception in our American cities today it is to the advantage of the public to use any gain in efficiency to improve street lighting results, rather than to reduce street lighting costs. The average street lighting system today is inadequate. The economic loss due to this condition is very considerable. Street lighting expenditures should be increased. It is expensive not to increase them. The asymmetric idea cannot take the place of this increase and much less can it justify a decrease. What it can do is to make the necessary increase in expenditure somewhat less than it otherwise would be. Asymmetric street lighting brings us closer to the day when our streets will be as safe by night as they are by day.

DISCUSSION

PRESIDENT-ELECT HATTON: Gentlemen, are there any questions you would like to ask of Mr. Rolph ?

MR. SHARP: All of the papers given tonight on street lighting mention in particular the effect of inadequate street lighting on traffic accidents. Statistics have been given which indicate

the relation between poor lighting and accidents. We recently had brought home to us in Cleveland an illustration of this fact. There are four main thoroughfares leading east from the public square, all of about equal importance. Considering only the sections of these thoroughfares lying between the public square and East 55th Street two of these streets have modern lighting systems, while the other two have very inadequate systems. In the year 1923 we took a check of the fatal accidents on these streets. During the daytime when, of course, the lighting conditions were equal, each pair of streets had practically an equal number of fatalities; ten on the first group, nine on the other. At night, however, the two well-lighted streets had only one fatality each, or a total of two, while the two poorly lighted streets accounted for fifteen fatalities. This was in spite of the fact that the well-lighted streets carried considerably more traffic than the poorly lighted ones. During the first eight months of this year on one of these same poorly lighted streets there were eight deaths due to accident, caused by lack of adequate street illumination. Needless to say, the City of Cleveland has taken steps to provide a lighting system of the highest order on these dark streets.

POWER PLANT DEVELOPMENT

By T. J. Lucas, Chief Engineer of Illinois Power & Light Corporation

The term "Power Plant Development" embraces much more than the mere history of the growth of the central station. It involves the idea of the growth of an industry with its many ramifications and allied arts. It includes certain related institutions, such as regulating commissions, taxing and legislative bodies, and financing organizations. It embraces not only the consideration and development of the physical property, but of the financial and corporate structure as well.

Back in 600 B. C. Thales of Miletus, discovered that amber, jet, and other substances when rubbed with cloth, had the power to attract fragments of straw, leaves, feathers, etc. Thales named this property "Electrica" from amber, the Greek name for which was "electron." The fact was mentioned by Theophrastus, 321 B. C., and Pliny, 70 A. D. Not very much else was known with respect to this property through all of the centuries that followed, up to about 1600. Beginning with the investigations of Gilbert at the beginning of the seventeenth century the science was developed to its present state. This modern development can be divided into four periods. The first extended from the time of Gilbert, 1600, to the discovery and invention of Volta in 1799. The second period extended from thence to the publication of Farraday's results in 1831. The third period extends from Farraday to the time of J. Clark Maxwell in 1873. The fourth period extends from Maxwell's publication, to the present.

The first period was lead by Gilbert's study of magnetism which opened the field of modern investigation of electric science. It is the period of awakening of general scientific investigation, the end of the dark ages. This may be called the period of investigation of static electricity or stationary electric charges (that elusive substance which has manifested itself to most of you through interference in your radio apparatus) although towards the end of this period dynamic or flowing electricity was receiving attention, that form of electricity with

which you are familiar through the many uses which you now put it to for light and power. Quite a number of laws governing electricity were developed at that time. It appears that magnetism and electricity were in the main considered separately, their intimate relation not then being apparent.

The second period was introduced by Volta's discovery in 1799 of the Voltaic pile, the forerunner of the modern battery, together with his investigation of the kinetics or movements of electrical current. Oersted discovered and investigated the relation between electricity and magnetism. This period might be called that of electric dynamics.

The third period was marked by Farraday's exposition of induction in 1831. He introduced the idea of lines of force, definitely linking magnetism and electricity. This period might be called that of quantitative research, and marked the first important practical applications.

The fourth or modern period, was introduced by James Clark Maxwell with his mathematical investigations, his theory of dielectrics, and more than all, his dynamic theory of light. It was he who first correlated the phenomena dependent on the ether. This period may be called that of commercial application of electrical energy.

On September 4, 1882, the first central station in the world initiated service. This was the Pearl Street Station in New York City, and came into being as a result of the work Edison was doing in Menlo Park, where he produced the first paper carbon incandescent lamp, the energy for which was supplied by storage batteries. This Pearl Street Station was built and put into service by the Edison Electric Illuminating Company of New York City, the company formed by Edison and his associates to put the results of his experimental work into practical operation. You will note how comparatively young the industry is when mention is made of the names of a few of the men present at the commencement of operations, still prominent and active in the public service industry: Thomas Edison, Samuel Insull and J. W. Lieb, at present vice president of the New York Edison Company. While there were earlier commercial applications of electrical energy, including the use of are lamps, such earlier uses were not really those of the Central Station, and it may properly be said that the Pearl

Street Station marked the birth of the great Central Station industry.

It may be of interest to review briefly the progress of the Central Station industry through reference to the size of generating units and the size of generating stations in various decades since the start of the Pearl Street Station. The Pearl Street Station itself had 125 h.p. so-called "Jumbo" generators, six in all. At the time of the World's Fair in Chicago. in 1893, there were installed units of 1000 h.p. each, or, as was stated, 15,000 lights capacity. In 1903 the first major turbine driven Central Station was constructed and put into operation. This was the Fisk Street Station of the Commonwealth Edison Company of Chicago, containing individual units of 6,700 h.p. later replaced with 11,000 h.p. units and at present containing units of 40,000 h.p. In the next decade the size of individual units had risen to 40,000 h.p. and at present there are individual units of 80,000 h.p. in operation with units of 135,000 h.p. contemplated. The Pearl Street Station totaled 750 h.p., the original Fisk Street installation in 1905 was 20,000 h.p. Hell Gate Station, New York, contains 350,000 h.p., and the Crawford Avenue, Chicago plant, is planned for 1,000,000 h.p. ultimate capacity.

With the increase in the size of units there were corresponding increases in the operating steam pressures, and whereas the units in the earlier days operated under a steam pressure of 50 or 60 pounds, at the present time, modern stations are operating at pressures between 300 and 500 pounds, with one or two stations possessed of units which will operate at a pressure of 1,200 pounds and higher pressures are in contemplation. At the same time the temperature of the steam has been increased from approximately 300° Fahrenheit to 750° Fahrenheit. Corresponding increases in efficiency of generation were had as a result of the increase in the size of units and the increase in pressure and temperature of the steam, until today a unit of electricity is being produced with approximately 1/15 of the amount of coal required in the very early stations, and in fact, the economy in fuel has been doubled in modern stations in the last five years.

To further illustrate the growth of the Central Station industry in the United States, it may not be amiss to mention the