Page:Scientific Memoirs, Vol. 2 (1841).djvu/82

70 2. Experiments of vibration.

Consequently the time of one vibration $$t = 6''\cdot 67$$.

3. Application of the observations.

A general and intelligible view of the application of these observations, without entering into theoretical considerations, will be best given by extracting certain passages from a memoir in Schumacher's Jahrbuch for 1836, entitled, "Ueber Erdmagnetismus und Magnetometer;" and adding the mathematical expressions of the laws there given verbally.

"The square of the number of vibrations made by a magnetic needle in a given time, is a measure of the intensity of the earth's magnetism which depends on the needle employed. The individual properties of the needle have a two-fold influence:—first, by the greater or less magnetic force which it possesses; and secondly, by the effect of its form and weight on the time of vibration. The elimination of the latter effect presents no difficulty. The influence of the earth's magnetism on the magnetism of the