He tried other metals, but they were either alloys or impure. Those named in the list above were the pure metals. However, he carried on experiments with sheets of many different substances, and arrived at the following table, which shows particularly the relative transmitting and reflecting powers of the various substances in the rough.
Impression by Impression by Reflecting Transmitted Rays. Reflected Rays. Body
Copper None Fairly strong but much less than zinc
Lead None Very strong but a little weaker than zinc
Silver Strong, a thin plate Weaker than copper being used
Mica Very strong Very strong about like lead
By comparing, as in previous experiments, the intensity of the photographic impression by reflected rays with an equivalent impression due to a direct exposure of the same bulb and at the same distance, that is, by calculations from the times of exposure under assumption that the action upon the plate was proportionate to the time, the following approximate results were obtained:
Impression Reflecting by Impression Body Direct by Action Reflected Rays.
He stated that while these figures can be but rough approximations, there is, nevertheless a fair probability that they are correct, in so far as the relative values of the sciagraphic impressions of the various objects by reflected rays are concerned.
In order to devise means for testing the comparative reflecting power in a more decided manner, he laid pieces of different metals side by side upon a lead plate. Consequently the reflecting surface was formed of two parts corresponding to the two metals. § 80. The vertically perpendicular partition of lead served to prevent the mingling of the rays from the two metals. Ingenious precautions were taken; as for example, so arranging matters that upon equal areas of the two plates, equal amounts of X-rays impinged. § 80. He undertook to determine the position of iron in the series by thus comparing it with copper. It was impossible to be sure which metal reflected better. The same regarding tin and lead and also in reference to magnesium and zinc. Here, a difference was noticed, namely that the magnesium was a better reflector.
He has made practical application of the power of the substances to reflect a certain per cent. of the rays by employing reflectors for the purpose of reducing the time required for exposure of the photographic plates. It admits, he stated, of the use of reflectors in combination with a whole set of discharge tubes, whereby rays which would be otherwise scattered in all directions are brought more nearly to a single direction of propagation.