=X-ray Lamp.= A high vacuum tube lamp whose interior walls are covered with crystals of calcium or other fluorescent substances, and which, when exposed to the X-rays, give out a luminous light. Y =Yoke.= A piece of soft iron which connects the ends of two portions of a core on which wire coils are wound. It is located at the ends farthest from the poles. The soft-iron bar placed across the ends of a horseshoe magnet to retain its magnetism. Z =Zinc-battery.= A battery which decomposes zinc in an electrolyte, thereby producing a current. =Zinc Currents.= Negative currents. =Zinc-plating.= The employment of zinc in electro-plating. THE END Transcriber’s Notes Inconsistent spelling, hyphenation, etc. have been retained, unless mentioned under Changes Made below. Technical descriptions have been kept as printed, even when they seem doubtful, wrong or dangerous. Depending on the hard- and software and their settings used to read this text, not all elements may display as intended. Changes Made Footnotes and illustrations have been moved outside text paragraphs. Where letters (such as V or L) are used to denote a shape rather than the letter, they have been transcribed as [V] or [L] for consistency with other, similarly used letters such as [U]. Some minor obvious typographical errors have been corrected silently. Page 108: "called Nobile’s pair" changed to "called Nobili’s pair". Page 182: "shallacked" changed to "shellacked". Page 184: "(A, B, and C) and A A, B B, and C C)" changed to "(A, B, and C and A A, B B, and C C)". Dictionary: several entries have been moved to their proper alphabetical position. Page 334: "modern applications of phenonema" changed to "applications of phenomena Page 372: "Coil, Ruhmkoff" changed to "Coil, Ruhmkorff". Page 382: "Daniells" changed to "Daniell". Page 396: "graphite a native; form of carbon" changed to "graphite; a native form of carbon". Page 401: "Ruhmkoff Coil. (See Coil, Ruhmkoff.)" changed to "Ruhmkorff Coil. (See Coil, Ruhmkorff.)"