Page:Scientific Memoirs, Vol. 2 (1841).djvu/77

Rh were made, not according to the time of the place, but simultaneous with those of Göttingen, the comparison of the single days would afford an opportunity for other combinations, which, when continued through a considerable time, would possess great interest. Observers who follow this plan, i. e., of making the times of observation simultaneous with ours, are requested to communicate the daily observations; this may be done in divisions of the scale, provided the necessary elements of reduction are at the same time communicated. 2em

IV.

Description of a small portable Apparatus for measuring the absolute intensity of Terrestrial Magnetism.

Among the numerous applications of the magnetometer, the most important is that of measuring the absolute intensity of the earth^s magnetic force, as described in the memoir entitled, Intensitas vis magneticæ terrestris ad mensuram absolutam revocata; Auctore Carolo Friderico Gauss: Göttingen, 1833. Frequent mention will be made in the course of this work of this application of the magnetometer, which enables us to compare numerically with one another the results of experiments made in the most distant parts of the globe, at different epochs, and with apparatus not previously compared. Everything necessary to be known for these experiments, as well as everything that may serve to facilitate them, will be communicated from time to time. Results of such absolute measurements will also be noticed, and their value shown in establishing, on a scientific basis, the science of galvanism.

These important absolute measurements can be performed with the accuracy they deserve only with the magnetometer, and, indeed, only in a completely furnished observatory. Few such observatories, however, exist at present, and few philosophers, therefore, have these means at their disposal; while there are many who take an interest in the results, and desire to be enabled to form such an opinion concerning them as can hardly be satisfactorily obtained without actually taking part in the observations and calculations, even though less minute and accurate. The simple means which it is the object of this chapter to describe may be procured by every person. The description and mode of employing them are with the more propriety given VOL. II. PART V.