TO MAP OUT ANY SPECTRUM.

Place the eye-piece with cross wires in the telescope, with the cross in the shape of an X. Then move the telescope so that the point where the wires cross comes successively in contact with the various lines, noting the readings of the nonius on the arc. From these readings, by the help of any mechanical scale of equal parts, a map may be easily constructed.

By the assistance of spectrum analysis four new metals have been discovered, viz. Cæsium, Rubidium, Thallium, Norium. It is often a cause of grumbling with young beginners in chemistry that there is so much washing of glasses and slopping required to obtain proper results from tests; but here is a most refined mode of testing, which may be carried on in the drawing-room, and so delicate that a portion of sodium salt even less than 1⁄180,000,000th part of a grain can be easily detected.

Formerly the metal Lithium was considered to be a very rare one, but since the use of the spectroscope, quantities less than the 1⁄6,000,000th of a grain have been detected; it now appears that lithium is a very common metal, and exists in the human body, the sea, and may be obtained from many other common sources. Lithium has been found in the ashes of marine plants, the ashes of tobacco—in milk, coffee, tea, human blood, and in muscular tissue; it has also been found in meteoric stones.

The [coloured plate] is a faithful copy of Kirchhoff’s Diagram, and shows the solar spectrum, also the spectra of potassium, sodium, lithium, strontium, calcium, barium, rubidium.

PART IV.
Domestic Pets.