Nikola Tesla: Colorado Springs Notes, 1899-1900 Image VII (7)

VII. View of “extra coil” in action. Wires slightly inclined to the ground, to prevent discharge from going to roof, were fastened at small distances to brass ring on top of coil. Thus a great amount of streamers was produced and they were necessarily weaker individually. The plate illustrates well this feature as is evident from the hairlike appearance of the streamers. Individual sparks passing to ground sometimes are strong. It is peculiar that discharge will break out more strongly on some wire and then keep on the same place until broken by draught created or otherwise. The path is, however, evidently accidental depending probably on the arrangement of particles floating in the air. This photograph is very beautiful and symmetrical. The length of the streamers is about the same as in preceding case. The vibration of “extra coil” system about normal only slightly modified by the wires attached to brass ring. Some streamers, curious to note when striking the ground and thus becoming sparks or spark discharges more brilliant in color, appeared thicker on bottom than on the point of origin. I believe I have recorded this phenomenon some time before. It may, on the plate, appear that the streamer or spark is thicker farther away from the origin without necessarily being so. This is simply caused by the end or lower part of the streamer being closer to the camera than the origin. But the eye is not deceived in this respect and the phenomenon may be frequently noted so that its existence is beyond doubt. This may be explained by assuming a volatilization of the

material where the spark strikes, whereby a flame may be produced increasing the brightness of the part of the luminous path nearer to this point. In fact I observe that whenever a powerful spark strikes an object which is of a material easily disintegrated by the heat, such as wood, there is a momentary small flame produced on that point and often one may see the spark bound back as it were or splash over the object like a jet of molten metal. It will be noted on the negative that the points where the sparks hit the floor are always darker, this showing the increased development of light at these spots. The plate used is the same as before.

In plates VII, VIII and IX one hundred closures of the switch were made.