The manner in which we find the actinic power influencing electrical action, also shows us that the equilibrium of forces is continued through all the great principles of nature. If a galvanic arrangement is made, by which small quantities of metals may be slowly precipitated at one of the poles in the dark, and a similar arrangement be exposed to sunshine, it will be found that no metal is deposited: the sun’s rays have interfered with the decomposing power of the electrical current. At the same time we learn, that by throwing a beam of light upon a plate of copper which forms one of a galvanic pair, whilst it is under the influence of an acidulated solution, an additional excitation takes place, and the galvanometer will indicate the passage of an increased current of electricity. These two dissimilar actions appear enigmatical; but they may, there is no doubt, receive some solution from the influence of different rays on the contrary poles of the battery. One thing is quite evident,--electricity suffers a disturbance of one order, by light; and an excitement of another by its associated principles in the sunbeam. If a yellow glass is interposed between the galvanic arrangement and the sun, the electro-chemical precipitation goes on in the same manner as it would in perfect darkness, and no extra excitement is produced upon the plates of the battery. From this it would appear that actinism and not light is to be regarded as the disturbing power.[128] It has already been shown that yellow media possess the power of stopping back the chemical agent. We have already, detailed many of the peculiarities of the different varieties of Phosphori, which would seem to be the result of light. Phosphorescence is probably excited by those rays which produce no direct effect upon the eye. If we spread sulphuret of calcium upon paper, and expose it to the action of the solar spectrum, it is found to glow (in the dark) only over those spaces occupied by the violet rays and the ordinarily dark rays beyond them; proving that the excitation necessary to the development of the phenomena of phosphorescence is due to a class of rays distinct from the true light-giving principle, and more nearly allied to that principle or power which sets up chemical decomposition. Whether the fluorescent rays, before mentioned, which are found so abundantly over the space which produces the greatest phosphorescent effect, are active in producing the phenomena, is as yet an unsolved problem. Vision and colour, calorific action, chemical change, molecular disturbance, electrical phenomena, and phosphorescent excitation, all, each one with a strange duality, are connected with the sunbeam.