Nature the Original
Smelter

AN ingenious theory regarding the dis

covery of the art of smelting ores was advanced half a century ago by Bishop Watson in his "Chemical Essays.' The presence of gold, silver, lead, and probably copper, must in the earliest times have become in various ways too

obvious to allow the art of smelting the ores to have remained long undiscovered. The detection of virgin pieces, or the accidental effects of fire upon the more fusible ores, are circumstances which account at once for the early notions and strange fictions that existed among the ancients on this subject-especially the natural and poetic idea of the conflagration of a forest by the rubbing together of trees against each other during a high wind, and the consequent fluxion of some of the metal from ores lying exposed on or near the surface. Watson observed that "the earth in a little time after the deluge, and long before it could have been peopled by the posterity of Noah, must have become covered with wood; the most obvious method of clearing a country of wood is setting it on fire. Now, in most mineral countries, there are veins of metallic ores which lie contiguous to the surface of the earth; and these, having been fused whilst the woods growing over them were on fire, probably suggested to many nations the first idea of smelting ores :—

-Powerful gold first raised its head,
Brass and silver and ignoble lead,
When shady woods on lofty mountains grown,
Felt scorching fires; whether from thunder
thrown

Or else by man's design the flames arose, Whate'er it was that gave these flames their birth,

Which burnt the towering trees and scorched

the earth,

Hot streams of silver, gold and lead and brass, As nature gave a hollow proper place, Descended down and formed a glittering mass.' Whatever may be said of the greatness of the poet as such, there is no great natural absurdity in this notion of nature's smelting. Indeed, it is confirmed by the testimony of very ancient historians, who speak of silver and other metals being melted out of the earth during the burn

ing of the forests upon the Alps and the Pyrenees.

The Bishop goes on to give many instances of fluxing of metals by the heat from fierce conflagrations.

Changes on the Moon

WE

E have all been taught-that is, those of us who have been taught at all that the moon is a burned-out cinder, a dreary, changeless waste, a silent, lifeless body, in which the only variation is from the scorching intensity of the heat at midday to the colder than Arctic temperature of the night; that of atmosphere there is none; and that moisture does not exist.

But now it seems that all this is wrong. Not only is the surface of the moon changing; but there is every evidence of moisture and vegetation. At least this is the only plausible explanation that can be given for the phenomena that have been observed.

As to the first point, the change of surface is attributed to volcanic action, showing that the moon is not quite à cinder yet. The appearance of hoar frost on mountain sides at sunset, and its disappearance after sunrise, account for the second; while the growth of dark spots on the sunny slopes of the mountain, which cannot possibly be due to shadows, can be explained only on the basis of the existence of vegetation. So the old man is alive after all. Alive with the throes of internal energy and force; and with the external manifestations of a vegetation, of a character of which we have no knowledge, but which must be hardy in the extreme, in that it is capable of surveying the cold of a lunar night and can pass through the phases of spring, summer, and autumn growth and fruition in the short period of two weeks. Of course, the exact condition partakes, as yet, much of the character of a surmise; but with modern telescopes directed to the work, the true explanation of the changes can hardly be ranked among the impossibilities of the future.-Translated from La Nature.

I

N direct-current work, the electrical engineer is concerned with the relations between electromotive force, resistance, current, and power. These relations are determined by the applications of the following laws:

PRI, in which P is the power in watts expended in heating a circuit of Rohms' resistance, when a current of I amperes is forced through the circuit. Kirchhoff's Laws

I. When a circuit branches, the current in the main circuit is equal to the sum of the currents in the separate branches.

2a. When two or more sources of electromotive force are connected in

*From Instruction Paper on Alternating-Current Machinery, Part 1, written for the American School of Correspondence at Armour Institute of Technology.

series, the total electromotive force is the sum of the individual electromotive forces.

2b. When an electromotive force acts on a number of elements or things in series, it is subdivided into parts, each of which acts upon one of the elements, and the sum of these parts is equal to the total electromotive force. For example, an arc-light dynamo of which the terminal electromotive force is 3,000 volts, acts on 60 similar arc lamps connected in series. Neglecting the resistance of the connecting wires, each lamp is acted upon by one-sixtieth of the total electromotive force, or by 50 volts.

In alternating-current work, the electrical engineer is likewise concerned with the relations between electromotive force, resistance, current, and power. These relations are determined by the application of the same fundamental laws as in case of direct currents, but in more or less modified forms. A summary of the fundamental laws of alternating currents is here given simply for purposes of comparison:

1,

P

фг

12

FIG. 2

Power Law, for A. C. Circuits PEI Cos Ø, in which P is the power in watts delivered to a circuit by an alternator of which the "effective" terminal electromotive force is E volts, when it produces an "effective" current of I amperes in a circuit, and Cos is what is called the "power factor" of the circuit.

in the main circuit, which divides into two branches. The effective currents in the two branches are I, and I amperes respectively. The relation between I, I,, and I, is shown in Fig. 2. . The angles , and O, depend upon the relative values of the resistance and reactance of the respective branches. It is to be noticed particularly that the arithmetical sum of I, and I, is generally greater than I.

20. When two or more alternators (or transformer secondaries) are connected in series, the total effective electromotive force is the "geometric" (or "vector")

MAIN

sum of the effective electromotive forces of the individual alternators.

Example. Two alternators A, and A., Fig. 3, of which the effective electromotive forces are E, and E, respectively, are connected in series to supply mains. Then the effective electromotive force E, between mains, is the geometric sum of E, and E, as shown in Fig. 4. The angle O depends upon the positions, relatively to the field magnets, of the armature coils on the respective machines. 2b. When an alternating electromotive. force E acts upon a number of elements

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