From numerous experiments made on phosphorescent substances exposed to that light, this philosopher is of opinion, that those which are imperfect conductors of elec tricity are all susceptible of the luminous property, from the action of the solar rays ; that non-conductors shine imperfectly, or not at all ; and that most conductors give no light whatever. Orpiment, and some of the oxides t." arsenic, tin, zinc, and lead, are, however, exceptions to this rule ; as are the tnuriate of tin, and the sulphate and phosphate of lead. It appears, in addition to all this, which we confess we can reduce to nothing like an agree ment with any electrical hypothesis, that there are effects of this nature even more anomalous and unintelligible. Thus the non-conductors, and the conductors which re fuse to phosphoresce by feeble electrical discharges, be come luminous after strong ones; while the imperfect conductors, that phosphoresce by means of weak ells charges, is no light whatever, if the strength of the ex plosions s Increased. We forbear to quote any more of these experiments, partlybecause we can discover no con clusions to be drawn from them, and partly because we think that they require to be repeated and generalized in some other hands,_ But, in support of this analogy between phosphores cence and electricity, D1. Dessaignes farther observes, that the former property is affected by the presence of points. If fluor spar has the asperities that are produced by frac ture, it phosphoresces with great ease, whereas the entire and smooth crystal remains dark. The same happens to carbonate of lime, adularia, apatite, emerald, and corn rnon salt.
Similar results were obtained from rough and from smooth glass. But there is another remarkable circum stance in this case, namely, that if both sides of the plate of glass thus used be rough, it becomes phosphorescent throughout ; whereas, if one side be rough, and the other polished, it only shines when the former surface is in con tact with the heated support.
It is still more remarkable, that the hexagonal lime spar, terminated by three faces, in which the laminae of the pri mitive rhumb arc placed at 45° to the axis of the prism, shines throughout its whole substance, when one of these faces is in contact with the heated body ; but if the crys tal be split, so that the face of the lamina be applied in the same manner, it emits no light. In a similar manner, ar ragonite, phosphoresces, when the side of the prism is laid on the heated plate, but refuses to do so, if the base be placed on it. Diamonds, in the same manner, did not show any light When the sides of the primitive octohedron touched the plate, but phosphoresced in any other posi tion.
These phenomena are assuredly interesting in a great degree; and they arc, at the same time, more intelligible than the preceding. They are also confirmed by other experiments, in the phosphorescences that arc excited by exposure to light, and not to heat ; which seem similarly connected in some manner with the electrical susceptibi lities of the same bodies.
If transparent Iceland crystal be exposed to light, it ac quires very little phosphorescence, while its faces are po lished ; but if one of these be rendered rough, and then presented to the rays of the sun, it readily becomes lumi nous. In a similar manner, prismatic arragonite acquires very little light, when the smooth natural crystal is expos ed ; but if it he broken, it easily becomes luminous, in whatever manner the fracture may have been made. Phe nomena of the same kind, but less strongly marked, are observed, when apatite and chrysolite are treated in a si milar way. These, and similar experiments, were multi plied and repeated with diamonds, and other minerals; and the relations between the phenomena of electricity and of phosphorescence were thus rendered more evident. All the faces parallel to the primitive form were most easily and strongly electrified, but produced least phosphores cence when exposed to the rays of the sun ; while the other faces, whether these were natural or artificial, form ed on the edges of the lamina, were feebly electrified by friction, and soon lost their electricity; but were, on the other hand, highly phosphorescent. These results are singular and interesting ; and they tend to prove what we suggested at the beginning of this article, that the term phosphorescence was a word of very vague signification, applied to phenomena distinct in their natures as in their causes, and connected by no other bond than the common property of giving light under peculiar modes of treat ment.
All the bodies, nearly, that are susceptible of phospho rescence by friction, become luminous by heating, by elec. trization, and by exposure to light. This property is ge nerally diminished by overheating, as is the ordinary phosphorescence of the same hodies which is excited by more moderate degrees of heat ; yet glass thus treated still emits light when rubbed by a file. The phosphores cence on friction takes place alike in all the gases, and in vacuo. Our author has an hypothesis on this subject, which we do not well understand, and of which we do not see the necessity. He supposes that the phosphorescence is produced by a particular fluid, which is set in motion by light, by heat, by electricity, and by friction ; and that the process of overheating, or of long exposure to light, causes it to be dissipated. But this hypothesis will not explain how electricity restores this fluid when once lost ; nor indeed is it in any way tenable. We can only con clude, that whatever connection between the power of phosphorescence and electrization may exist, we are yet incapable of understanding its true nature ; and that it is necessary to accumulate many more facts, before we can arrive at any rational determination respecting any part of this very curious subject.