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Special Reports 



outside diameter with an axial hole 0.61 mm. in diameter. A cylinder of pyralin with 

 slightly greater diameter than 1.17 mm., and traversed by an axial hole 0.61 mm. in 

 diameter, was driven into the outer half of each hole. The four brass plugs nearer the 

 equatorial plane of the spool extended about 2 mm. into the holes D, the outer half of each 

 cylinder being removed from the extending portion. The holes EE were drilled with a 

 specially constructed right-angled drill, and enabled the counterboring, threading, etc., 

 to be done with facility. 



10. The wire for the coils was prepared and presented to the Department with great 

 kindness by the Research Laboratory of the General Electric Co. through the courtesy 

 of Dr. W. R. Whitney. Hard drawn copper wire about 0.76 mm. in diameter had its 

 diameter reduced to about 0.71 mm. by solution in nitric acid, to remove the surface 





Fia. 14. Horizontal Section of one Pair of Terminal-. 



which might have been contaminated by iron from dies used in previous operations. 

 This wire was then drawn through a series of circular diamond dies until an exceedingly 

 uniform diameter about 0.576 mm. was attained, and was wound directly from the dies 

 onto a spool 30 cm. in diameter. 



Before beginning to wind a coil, one end of the wire was annealed, to make possible 

 the rather sharp bends near the terminal, and was then pushed through the inner pyralin 

 bushing H" and the brass plug I" and brought out through the hole D, Figure 14. It 

 was then soldered (with dissolved rosin as flux) securely and axially to the projecting end 

 of the plug. The wire was then slowly wound on the groove under a uniform tension of 

 about 4 kg. until the second terminal was nearly reached. It was then clamped several 

 centimeters from the terminal and cut off at a suitable point. The end was then annealed 

 and pushed through the bushings H' and V and drawn through D. The end was then 

 pulled tightly until the wire lay in its groove between the clamp and the terminal and the 

 wire was soldered to the bottom of the plug /' while bent close to the marble surface. 

 The clamp was then removed and the wire sprang more accurately into its place in the 

 groove. All of the coils were wound in this manner. After preliminary micrometer meas- 

 urements, a successful effort was made to reduce small irregularities occurring close to the 

 terminals of the windings by tapping with a light hammer and small ebonite block. 



