equally mobile. An iron wire seems solid. It is so; some parts much more so than others. The surface that has been in closest contact with the die as the wire was drawn through, reducing its size by one half, perhaps, is vastly more dense than the inner parts that have not been so condensed. File away one tenth of a wire, taking it all from the surface, and you weaken the tensile strength of the wire one half. But, dense and solid as this iron is, its particles are as mobile within certain limits as the particles of air. An electric message sent through a mile of wire is not anything transmitted; matter is not transferred, but the particles are set to dancing in wavy motion from end to end. Particles are leaping within ordered limits and according to regular laws as really as the clouds swirl and the air trembles into song through the throat of a singer. When a wire is made sensitive by electricity the breath of a child can make it vibrate from end to end, ensouled with the child's laughter or fancies. Nay, more, and far more wonderful, the wire will be sensitive to the number of vibrations of a certain note of music, and no receiver at the other end will gather up its sensitive tremblings unless it is pitched to the keynote of the vibrations sent. In this way eight sets of vibrations have been sent on one wire both ways at the same time, and no set of signals has in any way interfered with the completeness and audibility of the rest. Sixteen sets of waltzes were being performed at one and the same time by the particles of one wire without confusion. Because the air is transmitting the notes of an organ from the loft to the opposite end of the church, it is not incapable of bringing the sound of a voice in an opposite direction to the organist from the other end of the church.

The extreme mobility of steel is seen when the red-hot metal is plunged into water. Instantly every particle takes a new position, making it a hundredfold more hard than before it was heated. But these particles of transferred steel are still mobile. A man's razor does not cut smoothly. It is dull, or has a ragged edge that is more inclined to draw tears than cut hairs. He draws the razor over the tender palm of his hand a few times, rearranges the particles of the edge and builds them out into a sharper form. Then the razor returns to the lip with the dainty touch of a kiss instead of a saw. Or the tearful man dips the razor in hot water and the particles run out to make a wider blade and, of course, a thinner, sharper edge. Drop the tire of a wagon wheel into a circular fire. As the heat increases each particle says to its neighbor, "Please stand a little further off; this more than July heat is uncomfortable." So the close friends stand a little further apart, lengthening the tire an inch or two. Then, being taken out of the fire and put on the wheel and cooled, the particles snuggle up together again, holding the wheel with a grip of cold iron. Mobile and loose, with plenty of room to play, as the particles have, neither wire nor tire loses its tensile strength. They hold together, whether arms are locked around each other's waist, or hand clasps hand in farther reach. What change has come to iron when it has been made red or white hot? Its particles have simply been mobilized. It differs from cold iron as an army in barracks and forts differs from an army mobilized. Nothing has been added but movement. There is no caloric substance. Heat is a mode of motion. The particles of iron have been made to vibrate among themselves. When the rapidity of movement reaches four hundred and sixty millions of millions of vibrations per second it so affects the eye that we say it is red-hot. When other systems of vibration have been added for yellow, etc., up to seven hundred and thirty millions of millions for the violet, and all continue in full play, the eye perceives what we call white heat. It is a simple illustration of the readiness of seeming solids to vibrate with almost infinite swiftness.

I have been to-day in what is to me a kind of heaven below--the workshop of my much-loved friend, John A. Brashear, in Allegheny, Pa. He easily makes and measures things to one four-hundred-thousandth of an inch of accuracy. I put my hand for a few seconds on a great piece of glass three inches thick. The human heat raised a lump detectable by his measurements. We were testing a piece of glass half an inch thick; and five inches in diameter. I put my two thumbnails at the two sides as it rested on its bed, and could see at once that I had compressed the glass to a shorter diameter. We twisted it in so many ways that I said, "That is a piece of glass putty." And yet it was the firmest texture possible to secure. Great lenses are so sensitive that one cannot go near them without throwing them discernibly out of shape. It were easy to show that there is no solid earth nor immovable mountains. I came away saying to my friend, "I am glad God lets you into so much of his finest thinking." He is a mechanic, not a theologian. This foremost man in the world in his fine department was lately but a "greasy mechanic," an engineer in a rolling mill.

But for elasticity and mobility nothing approaches the celestial ether. Its vibrations reach into millions of millions per second, and its wave-lengths for extreme red light are only .0000266 of an inch long, and for extreme violet still less--.0000167 of an inch.

It is easier molding hot iron than cold, mobile things than immobile. This world has been made elastic, ready to take new forms. New creations are easy, for man, even--much more so for God. Of angels, Milton says:

          "Thousands at his bidding speed,
        And post o'er land and ocean without rest."

No less is it true of atoms. In him all things live and move. Such intense activities could not be without an infinite God immanent in matter.