Hence, to obtain great sensibility along with a considerable range, we require very long slender stems, and to these two objections apply in addition to the question of portability; for, in the first place, an instrument with a very long stem requires a very deep vessel of liquid for its complete immersion, and, in the second place, when most of the stem is above xIv.
Mascart, Traite de magnetisme terrestre, containing a description of the instruments used in the French magnetic survey, which are interesting on account of their small size and consequent easy portability; H.
This instrument was made with a pendulum weight of I loo kilos or over a ton; and with a modified construction the weight was increased to 17,000 kilos or nearly 19 tons, portability being obtained by replacing the solid pendulum of the smaller instrument by a shell which can be filled with barytes, a heavy mineral readily obtainable in most places.
The advantages of portability, very considerable range (from H =I upwards), and fair accuracy are claimed for the instrument.
The advantages claimed for it were its cheapness, smallness and portability; that there was no appreciable distortion, and that its field was much larger than that of the camera obscura.
Its comparative cheapness, one dollar's worth being equal to three dollars' worth of opium in the effect produced, its portability and the facilities offered in obtaining it, are all in its favour.
Dissecting stands vary as to portability, the size of the stand, and the manner in which the arm-rests are arranged.