would be P. I. Our Laboratory Spectrometers Reading Device for Thermometer C1365, $4.00 Send for Catalo Are sold in competition with instruments of European make WM. GAERTNER AND CO. Physical and Astronomical Instruments 5345-49 Lake Park Avenue CHICAGO ELECTRIC OVENS Type T. R. Single Tube Rheostat No Laboratory Equipment is complete without some variable resistances. To maintain the high standard of your outfit we suggest the addition of some "Becbro" Sliding Contact Rheostats (Tubular and Stone Types) Thousands of these rheostats have been manufactured and sold by us (the original American Manufacturers) to most all Universities, Colleges, Technical Schools and Industrial Concerns and have always given entire satisfaction. Write for Bulletin C-5 BECK BROS. 3640-42 North Second Street Philadelphia, Pa CADMIUM STANDARD CELLS For use with potentiometers, electrometers, and ballistic galvane meters, or wherever else a precision standard of electromotive force 1 needed. Negligible Temperature Coefficient. Contents hermetically sealed in glass so that lowering of electr motive force due to evaporation is impossible. Mounted in moulded box, or unmounted. My comparison certificate accompanies each cell without charg On November 13, 1916, three normal cadmium celle made by m were certified by the Bureau of Standards as differing from their grou of reference cells by less than one part in one hundred thousand, a three having the same value. On March 30 1920, after the lapse of three years and four month the same three cells were again compared by the Bureau of Standard The maximum difference among the three was less than one part p hundred thousand, and the maximum difference from their certifie value of 1916, was less than one part per hundred thousand. In other words, these cells showed a degree of constancy to intents equal to that considered most highly satisfactory, if not remarl able, in the very best type of precision resistance standards. (a Bul. Bur. of Stand. Vol. 5, No. 3. p. 427.) The cells in question were in nowise special. They were ma of the materials regularly prepared by me, and were set up with 1 greater care than that constantly employed in the making of my sta dards. Marion Eppley, (A.M., Ph.D.) Physico-Chemical Apparatus. NEWPORT, R. I. In "The Outline of History." (Second Edition.) Cloth. $3.00. When Buffalo Ran It By George Bird Grinnell "It is hard to classify this book. might be called a straightforward narrative of real adventure in the fashion of Defoe; it might be called a book for boys who like to read romance of the old West; it might have been printed as a contribution to the sociology of the American Indian. In any case it is a remarkable story and as interesting as it is remarkable." The Literary Review, New York Evening Post. Illustrated. $2.50. The Dawn of Modern By Albert H. Buck A new book by Professor Buck describing the progress of medical science in Western Europe from the early part of the eighteenth century until about 1860. A volume through which every doctor can better understand the history of his profession. Fully illustrated. $7.00. The Heart and the Aorta The books above mentioned may be purchased at any bookstore or, if your bookseller is out of stock, may be ordered direct from the publishers. Yale University Press 143 Elm Street, New Haven, Conn. 19 East 47th Street, New York City An Interesting Harbor Scene by (1834-190 Like many other great mast Neil Whistler er preferred Pride ship and con Whatman by the nd a half. of 150 mbodied their glad ealers apers tes, MAC MICHAEL VISC SIMETER Particularly ada for the testing o varnishes and gls, especially heavy glues. Used by research chemists for special tests on oils. Employed also for testing a wide variety of materials, the viscosity range being from that of the thinnest liquid up to the thickest glue The Mac Michael Viscosimeter is portable weighing only about twenty-five pounds and is of rugged construction. It is easy to operate and tests can readily be made by those who have no technical ex perience. The rate of rotation of the cup can b regulated at will up to about 120 r.p.m. The motor is universal, so that only th voltage need be specified. Heating i accomplished through the electric heat ing plate. Experiments are being conducted lookin toward the standardization of the entir range of torsion wire used. The operato can standardize the lighter wires agains sugar or other solutions of known strength The dimensions of the cup and of the cylindrical plunger conform to the requirements for c.g.s. units. Above the dial is a wheel by means of which the dial can be turned back a know number of degrees, so that for very exact reading its position can be indicated o the scale of a reflecting telescope by attaching a mirror to the spindle. A bulletin is being prepared which will incorporate the results of the various test and give full details. In ordering advise voltage of electric current and approximate range of viscosity the materials to be tested, so that suitable torsion wires can be supplied. |