Chapter IV: PHYSICS, ELECTRICITY. ETC.--The Wave Theory of Light.--By

SIR WM. THOMSON.--Sound and light due to wave
vibrations.--Difference between vibrations of light and
sound.--Radiant heat.--Solar spectrum.--Luminiferous
ether.--How to measure wave lengths of light and the frequency
of vibrations.--With diagrams. 7448

The Limitations of Submarine Telegraphy. 7450

Williams' System of Coast Defense by Electrical
Torpedoes.--Full page of figures. 7451

New Electric Gas Lighter.--2 figures. 7452

Insulators for Telegraph and Telephone Lines.--9 figures. 7452

Electric Light in Theaters. 7452

Rings of Smoke.--5 figures. 7461