Dr. Brewster remarks, that the light of these phospho rescent bodies is similar to that of the sun, or any other luminous body. In the blue fluor spar, he also remarked, that the phosphorescent part of the mineral was arranged in strata or veins, parallel to certain veins diverging from a central line, by which the structure of this mineral is de termined. Each of these strata emitted a distinct light, as well in colour as in intensity. Some were purple, others yellowish-green, and others, again, white ; while some of them displayed no light whatever. It was also remarkable, that these different strata of light were beautifully defined, and far more numerous and minute than the strata of the mineral itself seemed to be, when subjected to a microsco pic examination. Thus the phosphorescence of Iluor de tects a structure which could not be discovered in any other manner.
The same philosopher discovered, that in the Brazilian topaz the colour was often of a fine orange, and that, in many cases, the external parts were phosphorescent, while the nucleus, or internal ones, displayed no light whatever. In general, it was also most brilliant in the outer laminae ; but, in other instances, again, the light was brightest in the laminx between the nucleus and the outer parts of the crystal. In one specimen, a faint phosphorescence appear ed and vanished at intervals in the nucleus, while the outer parts shone with a bright and steady lustre.* The singu larity of all these facts serves to teach us that we have yet much to learn on this subject, and to point it out as one that requires to he thoroughly examined, in the hopes that some more general laws may be established, such as to lead to a more satisfactory knowledge of its nature than we yet possess.
Dessaignes has also remarked, that the light of phos phorescent bodies is decomposed by the prism like ordi nary light. He thinks that it is of a blue colour in all the phosphorescent bodies which do not contain metallic ox ides, and that it may be rendered so when bodies which yield light of other colours are forced from them. Thus, if phosphate of lime from bones, which has a yellow light, the Spanish apatite, which shows a green one, and the green fluor, the light of which is also green, be freed from their iron by means of muriatic acid, they all yield blue lights.
The phosphorescence of minerals is proved to be inde pendent of combustion, because it is not affected by im mersing them in various gases. Lime, farther, is very lu minous in dry, and very dull in damp weather ; and, in ge neral, the substances which attract moisture strongly do not shine, except when they are united to a quantity of water less than that which would saturate them ; but it is not necessary that they should be totally deprived of it. If lime, strontian, and barytes, are thrown on sulphuric acid in a dry state, they do not phosphoresce, nor are they im mediately dissolved. But if the breath, or a moist vapour,
be applied, they immediately phosphoresce, and are, at the same time, dissolved. But we dare not pursue this curious subject farther without the hazard of far transgressing our limits.
General Observations on Phcisphorescence.
We must now take notice of some particulars belonging to this class of phenomena, which could not well have been included under any of the preceding heads.
Dessaignes, after saying what we willingly admit, that the phosphorescence of mineral substances is not affected by the nature of the gases in which they are placed, goes on to remark, that the light emitted by vegetable and ani mal bodies is increased in oxygen, and disappears in hy drogen, azote, and carbonic acid. With respect to the insects, N4 e have already said, that the contrary has appear ed the case to many accurate chemists, and the same is the fact respecting the marine luminous animals. It is easy to commit errors in this case by adopting an hypo thesis, because these luminous bodies lose their light after a short time, in whatever air they are confined.
Al. Dessaignes conceives that he has established a cer tain relation between electricity and phosphorescence ; and we shall here select a few of his most remarkable facts. Some of them, however, do not appear to us to bear much on the subject of this connection, or analogy, or by what ever name it is to be called. Among the " metallic pow ders," those of zinc and antimony are the most phospho rescent, and those of gold and silver are least so. In a damp state of the atmosphere, all these, as well as the me tallic oxides, lose their luminous qualities. Even in dry weather, antimony loses its power of phosphorescing, if it be rubbed in a metallic mortar ; whereas, in an insulated vessel, the light is very much increased. If glass be pounded in dry weather, it is far more luminous than when this is done in a damp state of the air. In wet linen, it loses that property entirely ; but it is not deprived of it, like antimony, by being bruised in a metallic mortar ; be cause it is, in a certain sense, self-insulated. Adularia, that it may phosphoresce briskly, must be pounded in an insulated or insulating mortar ; and, in all these cases, the handle of the pestle should also be an insulating substance. If, farther, glass be " calcined" till its phosphorescence is diminished, it resumes that property by being exposed on an insulated support, and subjected to a few electrical dis charges, or to a current of electrical matter. The same method succeeds with any other substances that have lost their luminous property by similar treatment. It is also remarked, that electricity does not succeed in restoring the phosphorescence of those substances that have been deprived of it by the light of the sun.