fic, or heating rays; and the luminous, or colourific rays, which produce vision and colour.

Sir H. Davy has, in some general facts of great interest, traced an analogy between the effects of the sun's rays and the agencies of electricity.

Why are the terms red-hot and white-hot used?

Because, when bodies are rendered luminous by great elevation of temperature, the light which they emit often appears dependent upon the heat to which they are subjected. There are, however, certain bodies which, at high temperatures, are remarkable for the quantity and extreme brilliancy of their light, independent of actual combustion; this is the case with several of the earths, but more especially with lime, a small ball of which, about a quarter of an inch in diameter, being ignited in the flame of alcohol urged by oxygen gas, emits light; having about thirtyseven times the intensity of an Argand lamp burner.Brande.

Lieutenant Drummond has proposed to apply this principle to the improvement of the illumination of light-houses; by substituting "for the Argand burners a small ball of lime ignited by the combustion of oxygen and hydrogen.' His experiments are described in the Philosophical Transactions, 1830, as follows:—

"From this small ball, only three-eights of an inch in diameter, so brilliant a light is emitted, that it equals in quantity about thirteen Argand lamps, or 120 wax candles; while, in intensity or intrinsic brightness, it cannot be less than 260 times that of an Argand lamp. These remarkable results are deduced from a series of experiments made lately at the Trinity House; and, having been repeated with every precaution, and by different individuals, there seems no reason to doubt their accuracy. In the best of our revolving. lights, such as that of Beachy Head, there are no less than thirty reflectors, ten on each side. If, then, a

single reflector, illuminated by a lime ball, be substituted for each of these ten, the effect of the three would be twenty-six times greater than that of the thirty. On account of the smaller divergence of the former it would be necessary to double their number, placing them in a hexagon instead of a triangle. In this case the expense is estimated at nearly the same. This method was tried lately at Purfleet in a temporary lighthouse, erected for the purpose of experiments by the corporation of the Trinity House, and its superiority over all the other lights with which it was contrasted, was fully ascertained and acknowledged."

Why are light and heat necessary to the existence of plants?

Because, in the sunshine, vegetables decompose the carbonic acid gas of the atmosphere, the carbon of which is absorbed and becomes part of their organized matter; and the oxygen, which is the other constituent, is thrown off.

Why do not plants flourish in the dark?

Because no oxygen is then produced by them, and no carbonic acid absorbed.

Light exercises a very remarkable influence upon the irritability of the sensitive plant. Thus, if a sensitive plant be placed in complete darkness, by carrying it within an opaque vessel, it will entirely lose its irritability, and that in a variable time, according to a certain state of depression or elevation of the surrounding temperature.

Again, Mr. Burnet finds that when a sensitive plant has been made to droop, if the part in which the moving power resides is blackened so as to absorb the light of the sun, the restoration of the plant to its natural state is very much longer before it takes place. He also finds that at the moment the expansion at the foot of the leaflets, or other parts, is touched, to produce the motion of the plant, it changes colour.Philos. Mag.

Why are certain bodies said to be phosphorescent?

Because, when heated to a certain point below incandescence, (an exceedingly high temperature without the production of any gas) they become luminous, without undergoing combustion. Oil, wax, spermaceti, and butter, when nearly boiling, are luminous.Brande.

Why are other classes of phosphorescent bodies called solar phosphori?

Because they become luminous when removed into a dark room after having been exposed to the sunshine. Of this description are Canton's, Baldwin's, and the Bolognian phosphorus, the latter named from its discovery by a shoemaker of Bologna.-Brande.

Wöhler, a German chemist, recommends, as likely to give phosphorus at a very cheap rate, to distil, by a strong heat, ivory black with half its weight of fine sand and charcoal powder. A silicate of lime is formed, and the carbonic oxide and phosphorus come

over.

Dr. Bache, of Philadelphia, states, that at the temperature of sixty degrees Fahrenheit, or upwards, carbon in the form of animal charcoal, or lamp-black, causes the inflammation of a stick of phosphorus powdered with it; the effect takes place either in the open air, or in a close receiver of a moderate size.

Bodies spontaneously phosphorescent belong to another class. Among these are the flesh of salt-water fish just before it putrifies, and decayed wood. The glow-worm and the lantern-fly, certain shell-fish, medusæ, &c. are also luminous when alive; and the hundred-legged worm, and some other worms and insects, shine brilliantly when illuminated. These phenomena, as well as the phosphorescence of the sea, will, however, be explained elsewhere.

The phosphorescence of fish has already been noticed, and attributed to animalculæ during putrefaction; whereas, from the experiments of Canton, and

of Dr. Hulme, it appears that "sea-fish become luminous in about twelve hours after death, that it increases till putrefaction is evident, and that it then decreases."

Why may flame in general be regarded as luminous gaseous matter?

Because hydrogen gas, probably, furnishes the purest flame which can be exhibited; for the flames of bodies which emit much light, derive that power from solid matter which is intensely ignited and diffused through them, and which in ordinary flames, as of gas, tallow, wax, oil, &c. consists of finely-divided charcoal.— Brande.

Dr. Ure, speaking of "the nature of flame, and of the relation between the light and heat which compose it," says, "The flame of combustible bodies may, in all cases, be considered as the combustion of an explosive mixture of inflammable gas or vapour with air. It cannot be regarded as a mere combustion at the surface of contact of the inflammable matter. This fact is proved by holding a taper, or a piece of burning phosphorus within a flame made by the combustion of alcohol. The flame of the taper, or of the phosphorus, will appear in the centre of the other flame, proving that there is oxygen even in its interior part.

Why does spirit of wine sometimes burn with various coloured flames?

Because of its admixture with different substances. Thus, from borax it acquires a greenish yellow tint; nitre, and the soluble salts of baryta, cause it to burn yellow, and those of strontia give it a beautiful rose colour; copper salts impart a fine green.

Dr. Ure, in his valuable Dictionary of Chemistry, (edit. 1830) gives the following recipe for the beautiful red fire now so effectively used to aid stage effect at the theatres:-40 parts dry nitrate of strontia, 13 parts finely powdered sulphur, 5 parts chlorate of potash, (hyper-oxymuriate) and 4 parts sulphuret of antimony.

Powder the two latter separately in a mortar, and then mix them on paper; after which add them to the other ingredients, previously powdered and mixed. No other kind of mixture than rubbing together on paper is required. Sometimes, a little realgar is added to the sulphuret of antimony; and frequently, when the fire burns dim and badly, a very small quantity of finely powdered charcoal, or lamp-black, will make it perfect.

Why is working in coal mines sometimes fatal to miners?

Because of the carburetted hydrogen gas, or damp, and noxious exhalations, during the working of the coals, from fissures or cracks in the beds; when this has accumulated so as to form one-thirteenth of the atmosphere of the mine, it becomes explosive by a lighted candle or any kind of flame. By miners, this gas is called fire-damp, to distinguish it from carbonic acid gas, which they call choke-damp.

The late Mr. Spedding, having observed that the explosive damp could only be kindled by flame, and was not liable to be set on fire by red-hot iron, nor by the sparks produced by the collision of flint and steel, invented a machine, in which, while a steel wheel was turned round with very rapid motion, flints were applied to it, and by the abundance of fiery sparks emitted, the miners were enabled to carry on their work in places where the flame of a lamp or candle would occasion dreadful explosions.

Why is the safety-lamp so called?

Because it consists of a lamp surrounded by a wiregauze, which, by confining the flame from the firedamp, without intercepting the light, enables the miners to work in safety; and which, in gratitude to its illustrious inventor, Sir H. Davy, is, in mining districts called the Davy.