some spontaneously inflammable gas most probably by some of the compounds of phosphorus and hydrogen. That such gases are not always ignited as they escape into the air, is probably due to the different quantities of air with which they are mixed, or to the absence of the phosphoretted hydrogen. It has been suggested, and apparently with good reason, that, possibly, the cause of the sudden change in the position of the light is due to the collection of a large quantity of this gas near the surface, that is gradually ignited in spots, either by the presence of a neighboring flame or by the sudden liberation at that place of the necessary phosphoretted hydrogen.

It has also been believed that there may be another cause for the light of the ignis fatuus. Sir Isaac Newton suggests that this light is due to the presence of a species of phosphorescent light, like that of the firefly or the glowworm.

It is possible that some varieties of the ignis fatuus are of this general character. It is improbable, however, that this is frequently the case; since most of the ignes fatui are caused by the burning of an inflammable gas liberated from the marshy land, and produced by the decomposition of vegetable matter.

CHAPTER XXVI

SO-CALLED PERPETUAL LAMPS OF THE ANCIENTS

Since in ordinary lamps the light is as much due to the oxygen of the air as to the oil or other combustible, lamps will properly come under the subject of atmosphere.

It is an unquestioned fact that many of the sepulchres of the ancients, when opened, were found to contain airtight vessels, bearing inscriptions to the effect that lighted lamps were shut up in them, that would continue to burn and give off light forever. Moreover, when such vessels were opened, flames actually issued from the lamps within. It seemed, therefore, that the lamps had been burning ever since the sepulchres were sealed up.

Such lamps are so wonderful that we should try to find out what is known concerning them. In one of the chapters of a very curious book, published in London in the year 1708 by John Wilkins, Bishop of Chester, considerable attention is given to the question of what was known to the ancients as subterranean lamps.

Among other stories told by Bishop Wilkins is that concerning the lamp of a man known as Olibius. This lamp, it is claimed, continued burning for 1,500 years. A countryman, while digging in the neighborhood of Padua, Italy, came across an urn or earthen pot, inside of which was found another urn, and in this second urn a burning lamp. On each side of this there were two other vessels, each of them filled with a pure liquor, one of gold and the other of silver. It is uncertain, however, what relation, if any, these other vessels had to the burning lamp.

Another story is told of a lamp that was found in the

tomb of Pallas, the Arcadian, who was slain by Turmus in the Trojan War (which occurred possibly about 1104 B. C.). This lamp was burning when opened in the year 1401, from which it might seem that it had been burning for over 2,500 years. Wilkins says concerning this lamp that "being taken out, it did remain burning, notwithstanding either wind or water with which some did strive to quench it; nor could it be extinguished till they had spilt the liquor that was in it."

It may have seemed to you while reading these accounts that it would be impossible for a lamp actually to continue burning for so long a time. Such a conclusion would, indeed, be quite correct; for light, like heat, is only a form of energy, and cannot be produced without the expenditure of energy. So that supposing a lamp could be constructed that would require the consumption of an exceedingly small quantity of energy, yet, after a while, such a store would at last be exhausted, and the lamp would necessarily cease burning-not in a hundred years, nor, indeed, in a single year, but most likely in a few days at the most. Moreover, all cases of combustion with which we are acquainted requires not only the presence of a combustible body, that is, a body capable of burning, but also the presence of another body capable of entering into combination with it, and thus causing the burning; and this is generally the oxygen of the air.

We can safely conclude that such lamps were not burning during the time claimed. It is possible, however, to explain readily and simply how lamps might have been constructed that if buried over 2,500 years ago, or for the matter of that 5,000, or 10,000 years ago, would be found burning when opened and thus exposed to the air.

I will endeavor to explain how very simple this apparently wonderful thing is. In the first place the people who sealed the lamps in the air-tight vessels knew that they would be spontaneously lighted as soon as the materials with which

they were filled came in contact with the air. The people who opened them, expecting to find them burning, and on seeing the flame, believed that they had been burning from the time they were sealed up in the vessels.

As you can see, this explanation is not unlike the explanation of the light of the ignis fatuus. Only in the case of the ignis fatuus, the inflammable gas, produced by the gradual rotting or decomposition of vegetable or animal matter, is ignited immediately after it is formed, or as soon as it escapes through the water of the marsh and comes in contact with the oxygen of the air. But in the case of the so-called perpetual lamp, instead of the ordinary oils and wicks found in common lamps, they probably consisted of chemical substances of such a nature as to instantly ignite when the vessel containing the lamp was opened, and the oxygen of the air was thereby permitted to come in contact with them. This ignition occurring almost instantaneously, it appeared to those opening the lamp that it had been actually burning from the day it was sealed up.

I will not pretend to say that I know just how such lamps were made. Assuming the above explanation to be true, which by the way is one of the explanations that Bishop Wilkins mentions, but does not seem disposed to believe, I will say that I feel sure that I could devise a lamp of this character.

During the times when such lamps were buried in sepulchres, little or nothing was known of chemistry. There was, however, a study known as alchemy, which may be regarded as the beginning of the science of chemistry. A belief existed that it was possible, by subjecting the commoner metals, such as lead, iron, tin, etc., to certain operations, to convert them into gold. In order to bring about such changes, the alchemists tried many curious experiments, during which they subjected all kinds of substances to various processes somewhat resembling baking, boiling, frying, or roasting by fire; or they endeavored in various ways to change solid

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substances into liquids by subjecting them to the action of various solvent liquids. Now, the processes to which the materials were subjected were not unlike the processes employed to-day by chemists. So it came to pass that some very curious facts in chemistry were discovered.

Of course, the alchemists were unsuccessful in discovering what they called the Philosopher's Stone, or a substance by which the baser metals could be transformed into gold. They did, however, obtain curious bits of information which they were able to sell; so that when the custom arose among the very wealthy people of burying, with the bodies of their loved ones, lamps that it was claimed would continue burning forever, an opportunity was afforded the alchemists to make gold or money in another way. I do not doubt that much money was thus made, and a rivalry existed between different alchemists in the preparation and sale of their so-called perpetual lamps.

Let us suppose, for example, that some of these alchemists in their experiments had discovered two very common chemicals, namely, phosphorus and a liquid known as carbon bisulphide, a combination of carbon and sulphur. Now, this liquid possesses the power of completely dissolving phosphorus, producing a golden colored liquid, possibly the golden colored liquid referred to in one of the stories I have quoted from Wilkins of the perpetual lamps.

Suppose a lamp containing an ordinary wick were filled with carbon bisulphide in which a lot of phosphorus had been dissolved, and quickly shut up in an air-tight vessel; I have no doubt such a lamp would spontaneously ignite when the vessel was opened. If you doubt this, let me tell you of a simple experiment that can be tried, although I must caution you if you think of repeating this experiment, to be very careful, as you might otherwise set either yourself or your house on fire.

Having dissolved a small piece of phosphorus, say as large as a grain of rice, in about half a teaspoonful of carbon