A recent wonder of electric art is its penetration by a photographic ray of substances until now called opaque. Professor Roentgen's account of how he wrought this feat forms one of the most stirring chapters in the history of science. Next follows an account of the telegraph as it dispenses with metallic conductors altogether, and trusts itself to that weightless ether which brings to the eye the luminous wave. To this succeeds a chapter which considers what electricity stands for as one of the supreme resources of human wit, a resource transcending even flame itself, bringing articulate speech and writing to new planes of facility and usefulness. It is shown that the rapidity with which during a single century electricity has been subdued for human service, illustrates that progress has leaps as well as deliberate steps, so that at last a gulf, all but infinite, divides man from his next of kin. At this point we pause to recall our debt to the physical philosophy which underlies the calculations of the modern engineer. In such an experiment as that of Count Rumford we observe how the corner-stone was laid of the knowledge that heat is motion, and that motion under whatever guise, as light, electricity, or what not, is equally beyond creation or annihilation, however elusively it may glide from phase to phase and vanish from view. In the mastery of Flame for the superseding of muscle, of breeze and waterfall, the chief credit rests with James Watt, the inventor of the steam engine. Beside him stands George Stephenson, who devised the locomotive which by abridging space has lengthened life and added to its highest pleasures. Our volume closes by narrating the competition which decided that Stephenson's "Rocket" was much superior to its rivals, and thus opened a new chapter in the history of mankind. GEORGE ILES. CONTENTS FRANKLIN, BENJAMIN LIGHTNING IDENTIFIED WITH ELECTRICITY Franklin explains the action of the Leyden phial or jar. Suggests lightning-rods. Sends a kite into the clouds during a thunderstorm; through the kite-string obtains a spark of lightning which throws into divergence the loose fibres of the string, just as an ordinary electrical discharge would do. 3 FARADAY, MICHAEL PREPARING THE WAY FOR THE ELECTRIC DYNAMO AND MOTOR