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32 the platinum wire and the accumulators, and consequently the strength of the current, but not sufficiently for the observer to perceive a variation in the glow of the wire. In spite of this, the electrometer was deflected three divisions of the micrometer in the eye-piece. The following is another verification: raising the temperature of the wire one degree would alter its resistance in the ratio of about 1.004 to one; the difference of potential between A and B would alter in about the same ratio, since, the resistance external to the wire being very great, the current strength does not change. In my experiments this variation would deflect the electrometer by fifteen divisions. As absolutely no deviation occurred, and as, moreover, a quarter of a division could have been easily observed, the rise in temperature is certainly very inferior to $$\tfrac{1}{15} \times \tfrac{1}{4} = \tfrac{1}{60}$$ of a degree, and, consequently, quite insufficient to produce the observed increase in glow. It is thus super-abundantly established that the increase in glow produced by the rays is not due to a rise in temperature.

In the experiments with a plate of platinum,