The Boy's Playbook of Science / Including the Various Manipulations and Arrangements of Chemical and Philosophical Apparatus Required for the Successful Performance of Scientific Experiments in Illustration of the Elementary Branches of Chemistry and Natural Philosophy

by John Henry Pepper

The appearance of these bands of light is modified by the nature of the glass tubes employed, and the subject has been carefully investigated by Mr. Gassiott. At the last meeting of the British Association at Aberdeen, Dr. Robinson made various experiments, arranged by Mr. Ladd, for the purpose of showing the connexion between these miniature effects of bands of light in tubes containing various gases, and the phenomena of the Aurora Borealis. The title of the discourse, which was specially delivered in the Music Hall by the learned Doctor, was "On Electrical Discharges in Highly-rarefied Media," and it was illustrated by experiments prepared by Mr. Gassiott and Mr. Ladd.

The kind of tubes employed may be understood from the next figure. They are made in Germany, and by approaching a powerful magnet to the outside of any of the glass tubes whilst the bands of light are being produced, the most remarkable modifications of them are obtained. Mr. Ladd has mounted one of these tubes in a rotatory arrangement similar to that described at page 186.[page 186] When connected with the coil and battery, it furnishes one of the most lovely "electric fire-wheels" that can possibly be described. (Fig. 224.) Mr. Grove placed a piece of carefully-dried phosphorus in a little metallic cup, and covered it with a jar having a cap and wire. On removing the air from the receiver, and passing the current of electricity through it from the Ruhmkorff coil, he obtained a light completely stratified, and blended transversely with straight but vibrating dark bands.

Fig. 224.

a, b, c, d, e, f. Various tubes of different kinds of glass, and containing gases and vapours. Each tube has a platinum wire inserted at both ends, with which the contact is made with the coil. The tube a contains mercury, which has been boiled in it, and the air expelled. By moving the conducting wire to g or h, the light which otherwise passes through the whole of the tubes stops at these points.

Third Experiment.

When two very thin iron wires are arranged in the upright pillars (Fig. 223), and held sufficiently close to each other, as in Fig. 225, light passes from one to the other. The wire from which the light passes remains cold, the other becomes so hot that it melts into a little globule of liquid iron, and if paper is held between the wires it rapidly takes fire. (Fig. 225.)

Fig. 225.

Melting of the iron wire.