Page:Popular Science Monthly Volume 16.djvu/32

22. I will now try the same experiment with a bulb (B) that is very highly exhausted, and, as before, will make the side pole (a') the negative, the top pole (b) being positive. Notice how widely different is the appearance from that shown by the last bulb. The negative pole is in the form of a shallow cnp. The molecular rays from the



cup cross in the center of the bulb, and thence diverging fall on the opposite side and produce a circular patch of green, phosphorescent light. As I turn the bulb round you will all be able to see the green patch on the glass. Now, observe, I remove the positive wire from the top, and connect it with the side pole (c). The green patch from the divergent negative focus is there still. I now make the lowest pole (d) positive, and the green patch remains where it was at first, unchanged in position or intensity.

We have here another property of radiant matter. In the low vacuum the position of the positive pole is of every importance, while in a high vacuum the position of the positive pole scarcely matters at all; the phenomena seem to depend entirely on the negative pole. If the negative pole points in the direction of the positive, all very well, but if the negative pole is entirely in the opposite direction it is of little consequence; the radiant matter darts all the same in a straight line from the negative.