creed that he should rather be the first in the first rank of its philosophers and scientific benefactors." Appointed experimental chemist of the Royal Institution, London, in 1801, he immediately began a series of splendid discoveries which did much to establish the fame of the institution, founded a little earlier by Count Rumford, and which made the name of Sir Humphry Davy more widely known than that of any other scientific man of the age. Davy studied the theory and operation of the pile, but the major part of his important discoveries were really contributions to chemistry, made possible by the use of the electric current. They were based upon a most valuable observation by Hisinger and Berzelius, who noted, that, when the current decomposed a neutral salt or an oxide, the oxygen and acid were carried to the positive pole, and the base to the negative.

In this connection it is important to notice, that, in the earlier construction of the pile or battery, Volta's contact theory was strictly exemplified. In putting the plates together, the order copper, zinc, fluid; copper, zinc, fluid; and so on was adhered to, the series beginning with copper and zinc, and ending with the same. Erman of Berlin pointed out that the presence of the copper at the beginning, and

the zinc at the end, might be dispensed with, and that it was proper to say that the zinc end was the negative pole, and the copper end the positive. The same observation was made by Dr. Priestley, who at this time was experimenting in America. This explanation will account for an apparent error in Nicholson's description of his experiment, already quoted.

Davy saw in the voltaic battery a new and powerful means of producing decomposition. After experimenting extensively on already recognized compounds, he ventured to attack the so-called "fixed alkalies," whose composition was unknown. By greatly increasing the power of his batteries, and varying his arrangements in many ways, he was finally victorious. This famous experiment of October 6, 1807, he described as follows:

A small piece of pure potash which had been exposed for a few seconds to the atmosphere, so as to give conducting - power to the surface, was placed upon an insulated disk of platina, connected with the negative side of the battery, of the power of 250 of 6 and 4, in a state of intense activity; and a platina wire communicating with the positive side was brought into contact with the upper surface of the alkali. The whole apparatus was in the open atmosphere. Under these circumstances a vivid action was soon observed to take place. The potash began to fuse at

both its points of electrization. There was a violent effervescence at the upper surface: at the lower or negative surface there was no liberation of elastic fluid; but small globules, having a bright metallic lustre, and being precisely similar in visible characters to quicksilver, appeared, some of which burst with explosion and bright flame as soon as they were formed, and others remained and were merely tarnished, and finally covered by a white film which formed on their surfaces.

These small globules, with bright metallic lustre and resembling quicksilver, were globules of the metal base of potash, never before seen, and which Davy named "potassium." By a similar process sodium was obtained from soda ; and with great rapidity barium, strontium, calcium, and magnesium followed, and other more refractory compounds were attacked and conquered.

These decompositions so successfully accomplished by Davy must ever be regarded as constituting an epoch in the history of physical science. They were not only brilliant in their own right, but rich in the promise which they gave of the value of the new electricity in chemical research. They were at once repeated and extended by the most eminent chemists of the day, and with such important results that for nearly twenty years almost the sole use of

the electric current was for purposes of decomposition. But it was found to produce another effect, quite distinct from that referred to above, and calculated equally with that to attract the attention of the curious as well as to court investigation by the philosopher.

In the previous chapter frequent reference was made to the heating power of the older electricity, through which ignitions were brought about, metallic wires were melted, and so on. About the time that Davy was beginning his experiments, it was observed, probably first by Trommsdorff, that the voltaic current was capable of producing similar effects. The first experiment was made by attaching a piece of goldleaf to one pole of the battery, and touching it with a wire connected to the other. The goldleaf was rapidly consumed, producing beautifully colored flames. By improvements in the form of the battery, and especially by increasing its dimensions, very powerful heating effects were produced: long wires of iron, platinum, and other refractory substances, were fused. An experiment suggested by Dr. Wollaston gave a result which was at that time extremely curious, but which will receive its full explanation later on. It was that a greater length of thick platinum wire was ignited than another of the same substance but much smaller in

diameter. Davy did not neglect this heating power of the battery, and it is affirmed that he produced the electric light from carbon on a small scale as early as 1802. The remarkable discoveries which he had succeeded in making by the use of his battery of 250 cells produced such enthusiasm among all lovers and patrons of science, that he was enabled to continue his researches, assisted by one of the most powerful batteries ever constructed. It was erected in the Royal Institution, and consisted of 2,000 cells, with a total surface of 128,000 square inches. The metals of this battery were copper and zinc, and the liquid was a mixture of water, and nitric and sulphuric acids. When it was put in action the effects were extraordinary. They are described by Davy as follows:

When pieces of charcoal about an inch long and one sixth of an inch in diameter were brought near each other (within the thirtieth or fortieth of an inch), a bright spark was produced, and more than half the volume of the charcoal became ignited to whiteness; and, by withdrawing the points from each other, a constant discharge took place through the heated air, in a space equal to at least four inches, producing a most brilliant ascending arch of light, broad and conical in form in the middle. When any substance was introduced into this arch, it instantly became ignited; platina melted as readily in it as