THE UNKNOWN RAY AND ENTOGRAPHY.

It is difficult to name the unknown.  In the ancient world all the unknown was included in the idea of God.  It remained for the evangelist to declare that God is a spirit—­thus separating the natural forces of the material world from the Supreme Power who is from eternity.

This century has been the epoch of investigation into the nature of the imponderable forces.  Sound and light and heat have been known as the principal agents of sensation since the first ages of man-life on the earth; but their nature has not been well understood until within the memories of men still living.  Electricity was also vaguely known—­but very indistinctly—­from ancient times.  It has remained for the scientific investigators of our age to enter into the secret parts of nature and lay bare to the understanding many of the hitherto unknown facts relating to the imponderable agents.

The laws of heat, of acoustics, of light, have been clearly arranged and taught; but they have not been placed beyond the reach of new interpretation and possibly not beyond the reach of complete revolution and reconstruction.  That which has been accepted as definitely known with regard to these agents has now to be reviewed, and possibly to be learned over again from first principles.

As to electricity in its various forms and manifestations, that sublime and powerful agent began to be better known just before the middle of the century.  Since that time there has been almost constant progress in the science of this great force, until at the present time it is handled, controlled and understood in its phenomena almost as easily as water is poured into a vessel, air compressed under a piston, or hydrogen made to inflate a balloon.

It has remained, however, for the last half decade of the great century to come upon and investigate a hitherto unknown force in nature.  Certain it is that the new force exists, that it is everywhere, that it is a part of the profound agency by which life is administered, that its control is possible, and that its probable applications are as wonderful—­perhaps more wonderful—­than anything ever hitherto discovered by scientific investigation.

It is not unlikely that since the day, or evening, on which Galileo, with his little extemporized telescope, out in the garden of the Quirinal, at Rome, compelled bigotry to behold the shining horns of the crescent Venus, thus opening as if by compulsion the sublime vista of the heavens and bringing in a new concept of the planetary and stellar worlds,—­no such other discovery as that of the so-called Roentgen rays has been made.  The results which seem likely to flow from this marvelous revelation surpass the human imagination.  Let us try in a few words to realize the discovery, and define what it is.