Physikalisciie Zeitschrift. 12. Jahr-gang. 1911. Seite 540-546. Struktur und Optik grosser Kristalltropfen. Von O. Lehmann. Koxische Strukttjrstoerungen bei flues-sigen Pseudokristallen. Von o. Lehmann. Sonderabdruck aus den Ver-handlungen der Deutschen Physikal-ischen Gesellschaft. XIII. Jarhgang. Nr. 8. Braunschweig: Druck von Fried.!'. Vieweg&Sohn, 1911. TJber Molekularstruktcr und Optik grosser fluessiger kristalle. von o. Lehmann. Separat-Abdruck aus den Annalen der Physik. Vierte Folge. Band 35. Leipzig: Johann Ambrosius Barth, 1911. Die Uhw.odluxg tjnserer Naturauf-fassttko infolge der entdeckung des Relatiyitatsprixzivs. Von #Geh. Hof-rat Prof. Dr. o. Lehmann, Karlsruhe. Vortrag gehalten im Karlsruher Natur-wissenschaftl. Verein am 2 December 1910. Das Relativitatsprinzip deb neue Fun- dame.ntalsatz der PHYSIK. Von o. Lehmann, Sonderabdruck aus dem 23. Band der Verhandlunger des Natur-wissenschaftlichen Vereins. Karlsruhe: Druck der G. Braunschen Hofbuch-druckerei, 1910. These publications contain careful studies of Prof. Lehmann's investigation of liquid crystals. If there can be any doubt that our definition of the word “crystal” must be revised, surely Lehmann's work must dispel it. Dee Mensch der Vorzeit. Von Wilhelm Bolsche. Stuttgart: Kosmos, Gesellschaft der Naturfreunde, 1911. In this simply worded book the author gives the more important results of modern research on the subject of prehistoric man. "Say Mr. Jones, the bill clerk is ready to begin extending his bills and he wants the Comptometer." "Tell him he'll have to wait until I finish checking my postings." "All right, but how about Mr. Brown—he says to tell you he's been holding up s'ome percentage work for two or three days, waitin g for a chance at the machine?" "Well, I won't keep it long, but there's nothing doing until I get through." —This is typical of what happens in offices where they understand the Comptometer—where its value has been demonstrated by use on all kinds of figure work —addition, multiplication, division and subtraction. It won't cost you anything to have a Comptometer put in your office on trial. Write us about it. FELT&TARRANT MFG. CO., 1708 N. PAULINA ST., CHICAGO, ILL. Solders and Soldering t] If you want a complete text book on Solders and the art of Soldering, giving practical, working recipes and formulae which can be used by metallurgist, the goldsmith, the silversmith, the jeweler, and the metal-worker in general, read the following Scientific A merican Supplements: 1112, 1384, 1481, 1610, 1622, 1434, 1533, price 70 cents by mail. t] Order from your newsdealer or from MUNN&COMPANY, /nc. Publishers, 361 Broadway, New York AIRCRAFT THE WORLD'S GREAT MAGAZINE OF AERIAL FLIGHT A Collection of Issues Makes a Complete Aeronautical Encyclopedia Edited by Experts under Me General Supervision of Alfred W. Lawson Accurate Construction Work a Special Feature Complete Records and Statistics New Flyers Described Details of Model Building ILLUSTRATIONS FROM EVERY QUARTER OF THE GLOBE Recent numbers contain articles by such famous men as: Clement Ader, Louis Paulhan, Robert Esnault-Pelterie, Louis Bleriot, George F. Campbell Wood, Denys P. Myers, Hudson Maxim, Sir Hiram Maxim, A. Lawrence Rotch, Gen'l James Allen, Glen Curtiss, Chas. K. Hamilton, Claude Grahame-White, Major S. Reber, T. R. MacMechen, H. A. Wise Wood, The Hon. George Von L. Meyer, Secretary of the U. S. Navy, etc., etc. SUBSCRIPTION RATES $1.50 per Year $1.00 Eight Months 5Oc. Four Months Single Copies, 15c. Bound books, in cloth, first 12 numbers, $3.50. THE LAWSON PUB. CO. 37-39 E. 28th Street, New York, U. S. A. For Universal Service The Press and the Bell System The powerof the individual writer is multiplied by the printing press. In the same way the power of the individual telephone is multiplied by the Bell system. In both cases, increased usefulness comes from progress towards universal service. By means of the press the knowledge and thoughts of writers are spread throughout the land, maintaining among all the people the common language and the mutual understanding which makes for national co-operation. By means of the Bell system, each individual telephone becomes connectable with every' other telephone and each unit in the nation is given a personal membership in the most highly developed system of communication that the world has ever seen. The press prepares people for co-operation; the Bell telephone system enables them to really cooperate. The press educates people separately; the telephone enables them to act upon their mutual knowledge immediately and at any distance, By co-operation with telegraph and cable systems, universal service for communication is being made international. American Telephone and.Telegraph Company And Associated Companies One Policy One System Universal Service