124 Mr. E. L. Nichols on the Alternating 



lion by Messrs. Archbold and Teeple. Their experiments, 

 from which in great measure the data used in the first part of 

 this paper have been taken, are described at length in their 

 Thesis in Electrical Engineering, which is now in the library 

 of Cornell University*. 



The apparatus used in the verification of Mr. Acheson's 

 observation consisted of a Ruhmkorff-coil of moderate size, 

 the interrupter and condenser of which had been thrown out 

 of circuit. The primary coil, as in all instruments of that 

 type, consisted of a few turns of heavy wire surrounding a 

 core of iron wires. When this coil was supplied with current 

 from a small alternating-current dynamo, making 14,000 

 reversals a minute, and the terminals of the secondary coil 

 were brought into position, a discharge of considerable bril- 

 liancy took place between them. To the unaided eye the 

 discharge appeared to be perfectly continuous ; but the fact 

 that it was really of an intermittent and periodic character 

 was indicated by the emission of a well-defined musical note, 

 which corresponded in frequency with the period of alter- 

 nation of the dynamo. 



The terminals of the secondary coil were subsequently con- 

 nected with a brass ball about one centimetre in diameter, 

 and with a point consisting of a steel sewing-needle. These 

 were mounted horizontally in well-insulated bearings, the 

 centre of the ball in line with the axis of the needle. The 

 distance between the ball and the point of the needle was 

 capable of adjustment by means of a micrometer-screw. A 

 mirror-galvanometer of two thousand ohms, having in its 

 outer circuit about one hundred thousand ohms, was shunted 

 around the ball and point (in parallel circuit with the air- 

 space between them). When the induction-coil was put into 

 operation, the ball and point being too far apart to admit of a 

 visible discharge, the galvanometer-needle remained at zero, 

 but when they were brought within striking distance a large 

 and constant deflexion was produced. When the ball and 

 point were interchanged the deflexion was reversed, its direc- 

 tion always being that which would have resulted from a 

 current flowing from the ball to the point. Under the influ- 

 ence of the discharge, which was intensely luminous, the 

 steel needle was fused at the point and rapidly wasted by 

 oxidation, so that it became necessary to find some more 



* ' The Effect of placing a Ball and Point in a High Potential Alter- 

 .nating Current Circuit,' by W. K. Archbold and G. L. Teeple. Thesis 

 in MS., Cornell University Library, 1889. 



