APPARATUS AND METHODS. 

 I. Spark Apparatus. 



The source of light used in all of the work was a spark discharge from a 5-kw transformer made 

 according to special design by the Peerless Electric Company, of Warren, Ohio. The coils of this trans- 

 former are immersed in the best moisture-free oil and contained in a cyUndrical iron tank 83 cm in diameter 

 and 125 cm high. The primary and secondary leads are passed through the flat top of the transformer, 

 on which is a large knife switch for the regulation of the secondary voltage. The bar of this switch forms 

 the radius of a circle, one end being pivoted, while the other end fits into any one of a series of jaws along 

 the circumference of the circle. The connections with the transformer coils are such that the secondary 

 voltage may be 10, 20, 40, 80, 160, 320, or 640 times the impressed primary voltage, according to which 

 jaw the bar of the switch is titted into. Thus with 100 volts on the primary the secondary voltage is 

 1,000, 2,000, 4,000, 8,000, 16,000, 32,000, or 64,000, according to the connection. The use of a rheostat 

 in the primary circuit to regulate the impressed voltage will obviously give any secondary potential 

 desired up to 64,000 volts. The adjustable rheostat used is one capable of carrying heavy currents con- 

 tinuously. It is composed of sheets of tin cut into strips i cm wide by cutting almost across the sheet 

 first from one side and then from the other. The sheets of strips thus made are mounted vertically against 

 strips of asbestos fastened to a wooden frame, the distance between successive sheets being sufficient 

 to provide air circulation for coohng. Copper wires soldered to the tin strips at the proper intervals 

 lead to knife switches on the top of the rheostat frame. Various combinations of these switches place 

 parts of the tin resistance in series or parallel, and permit the resistance to be reduced by short steps 

 until all is out. One switch may be connected to an external resistance, thus allowing the latter to be 

 connected in series with any part of the tin resistance for fine adjustment of the rheostat. A bank of 

 twenty-four 32-cp incandescent lamps in parallel is usually used in this branch. 



The primary current is supphed at about 104 volts from one side of the three-phase connection of a 

 1 5-kw transformer. This transformer and one similar to it are mounted in the transformer room of the 

 laboratorj-, fed by 2200 volts from the lines of the Southern California Edison Company, and are used 

 together to supply the 208-volt three-phase current for the D.C. motor-generator set which furnishes 

 current to the electro-magnet. 



Two glass-plate condensers were used for the spark circuit during the series of experiments. The 

 more efficient one, used in taking the later photographs, is built up of 16 sheets of plate glass, of area 

 61 X 66 cm, and thickness 5.5 to 6.0 mm, laid horizontally in a strong, copper-Hned wooden tank. 

 Between the glass plates and at the top and bottom of the pile are sheets of copper, 17 in number, each 

 0.9 mm in thickness and with an area of 3330 sq cm, one side of each sheet having a tongue 2.5 cm long 

 projecting beyond the glass plates for the connection, while the plates immediately above and below are 

 cut away so as not to reduce the insulation at this point. Around the other three sides the copper is 

 cut so as to come 2.5 cm inside the edge of the glass plates. This arrangement, together with the form 

 in which the copper is cut on the fourth side where the tongues project, insures a distance of 5.7 cm 

 along the glass from the edge of one copper plate to the edge of the next. The condenser plates are sepa- 

 rated from the copper fining of the tank by a wood flooring 2.5 cm thick and held in place by a wooden 

 box inside the tank. A thick copper wire is soldered to each of the tongues coming from the copper plates 

 and the other end of the wire connected to a bincfing post set in a plate of fiber extending across the width 

 of the tank, 7.5 cm below the top. This fiber plate was at first placed level with the top, as shown in the 

 photograph of the laboratory (Plate I). This condenser is entirely immersed in the best transformer oil, 

 which fills the tank up to about 5 mm above the fiber plate, thus insulating the condenser plates and also 



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