Spectra; 3 kinds, dispersion, production of color effects, spectroscope, uses.
Nature of Light; wave theory, interference, polarization, significance.
[CHAPTER XVII]
INVISIBLE RADIATIONS
(1) Electric Waves and Radio-activity
415. Oscillatory Nature of the Spark from a Leyden Jar.—In studying sound (Art. 339), the sympathetic vibration of two tuning forks having the same rate of vibration was given as an illustration of resonance. The conditions for obtaining electrical resonance by the use of two Leyden jars are given in the following experiment.
Join the two coats of a Leyden jar (Fig. 413) to a loop of wire L, the sliding crosspiece M being arranged so that the length of the loop may be changed as desired. Also place a strip of tinfoil in contact with the inner coating and bring it over to within about a millimeter of the outer coating as indicated at G. Now join the outer coating of another exactly similar jar A to a wire loop of fixed length, the end of the loop being separated from the knob connected to the inner coating, a short distance at P. Place the jars near each other with the wire loops parallel and connect coatings of A to the terminals of a static machine or an induction coil. At each discharge between the knobs at P, a spark will appear in the other jar at G, if the crosspiece M is so adjusted that the areas of the two loops are exactly equal. When the wire M is moved so as to make the areas of the two loops quite unequal, the spark at G disappears.
