104 PROCEEDINGS OF THE AMERICAN ACADEMY. 



hiductance spark structure. 



70(a). 4810. Single order condition. Center of 3 mm. gap. Coil 

 (b) in circuit. Exposure: 30 seconds. Notice four components^ 

 the two outermost faint. 



Inductance spark structure and power in circuit. 



81 (b) and (d). 4810. Single order condition. Center of 1.5 

 mm. gap. Three layers of coil (a) as inductance. Two exposures 

 of 30 seconds each : (b) at 20 amp. and 1 hectowatt; (d) at 50 amp. and 

 2 hectowatts. These show that approximately doubling the current, 

 and the power in the primary of the transformer has little, if any, 

 effect upon the structure. This is confirmed by another photograph 

 in the case of 4722. 



Inductance spark structure as a function of the part of the image viewed. 



71 (a). 4722. Single order condition. Electric conditions as in 



70 (a). Exposure: 25 seconds. Three components are apparent 

 on the original negative, but the one toward the red is very weak. 



71 (c). 4722 Same as (a) but near end of image. Exposure: 

 35 seconds. Notice new component toward red not due to inequality 

 of exposure, for the main component is just as bright in 71 (a) as in 



71 (c). This effect is confirmed for 4810 by another photograph and 

 still further by: — 



111 (b). 4810. Center of photographic plate, central part of 4 

 mm. spark gap; outside of plate, end of gap. Coil (b) as inductance. 

 Notice the new component to red in the exposure of the end of the 

 gap. The original negative shows still another component toward the 

 red. Note further that despite the fact that the photographic image 

 of the central part of the gap is the denser of the two, the components 

 appearing are but two in number. Single order condition with the 

 left of the three central orders slightly stronger than the right, giving 

 a condition unfavorable for the appearance of components to the 

 right ! This is confirmed by three other sets of exposures. 



Effect of using an alloy. 



88 (a). 4810. Single order condition, center of 1.5 mm. disruptive 

 spark between brass terminals. Shows that the line structure is 

 simple although a continuous pattern is present with it, and that dis- 

 ruptiveness in itself is not the only controlling factor. Other ex- 

 posures with 5 and 9 mm. gaps gave the same results. 



89 (b). 4810. Same as 88 (a) except that three turns of inductance 

 were inserted. The result is a single fine line. 



89 (c). 4722. Same as 89 (b). Two fine lines, just separated, 

 appearing on the original negative. Photographs 89 (b) and 89 (c) 



