The attention of the scientific world has been for some years past fully awakened to the importance of observing the spectra exhibited during the combustion of chemical substances. But in making an extensive series of such experiments, it must often happen that the observer has to test substances of which he only possesses a very minute quantity. In that case, before he has viewed the spectrum long enough to feel fully satisfied of its nature, his stock of the substance is exhausted, and he is obliged to leave his observation imperfect. He might perhaps be testing some mineral in his cabinet, of which the native locality was unknown, and he might surmise it to contain a new metal, from its yielding a ray not before seen in the spectrum, yet after a short time his observations on it would come to an end, and he would have no means of showing this ray to other observers.