260 CARNEGIE INSTITUTION OF WASHINGTON. 



A conducting cement for attaching the fiber to the upper supporting lug has 

 been made. This is more convenient to apply than low-melting-point solder 

 and, as a number of tests show, is in other respects equally good. It consists 

 of shellac dissolved in alcohol and made conducting by the addition of fine 

 powdered graphite. 



Before finally attaching the two fibers of a bifilar element, the tension is 

 adjusted until the displacements of the fibers, which result when a small 

 electric heater is suddenly brought to a position about 10 cm. below them, are 

 equal. The frames of gilded fibers and also the mounted fibers when stored 

 in a dust-free place in the laboratory may apparently be kept without ap- 

 preciable deterioration for a number of years. 



Making an automatic focusing enlarger. C. A. Kotterman. Photo-Miniature, vol. 16, 

 405^51 (May 1923). 



The paper describes an enlarger by which focusing for different-sized images 

 is accomplished by a cam mechanism which automatically adjusts the positions 

 of the lens and negative with respect to the easel ; thus the enlarged image is 

 made to grow or shrink in size with perfectly sharp focus maintained, regard- 

 less of the degree of enlargement with the elimination of the trial and error 

 defect. 



Among the novel features of this apparatus is the employment of the 

 miniature-camera lens as the enlarging lens and the convertibility of the 

 device. In one form it is a self-contained oufit producing maximum enlarge- 

 ments of 8 by 10 inches from negatives or portions of negatives 2.25 by 3.25 

 inches and smaller. When used this way the outfit is operated very much 

 like a camera and requires no dark room. By means of a very simple adjust- 

 ment the self-contained form is readily converted into a modern projection 

 printer with a capacity of 8 degrees of magnification with the automatic 

 feature retained. 



Numerous photographs of the device as built by the author show the various 

 parts of the outfit in assembled and unassembled form; attention is called to 

 the importance of conjugate foci and the part played thereby in automatic 

 enlarging; the necessity of knowing the exact equivalent focus of the enlarg- 

 ing lens is emphasized; each part of the apparatus is then described in detail, 

 so that a duplicate may be constructed quite readily from the information 

 given. 



The monograph concludes with a short note on the design and construction 

 of special cams, with working formulas which may be followed in developing a 

 cam of proper size for a lens of any focal length. 



Notes on the production of quartz fibers. C. A. Kotterman. 



Quartz fibers in one form or another are frequently required for suspen- 

 sions of moving parts of apparatus, yet the articles by Boys^ and text-book 

 references^ give but meager information on methods for making such fibers. 

 The production of fibers of uniform diameter over considerable length and of 

 diameters 0.002 to 0.010 mm., suitable for use in electrometers, galvanometers, 

 and other delicate instruments, is a simple matter, but difficult for most 

 laboratory workers because of the lack of knowledge concerning the correct 

 procedure to follow. Accordingly, some experiments were made regarding 

 the suitable apparatus and methods for obtaining such fibers by the cross- 



' See Vernon Boys's "On the production, properties, and aome suggested uses of the finest 

 threads," Phil. Mag., June 1887 (also printed in Jour. Soc. Arts, 1889), and "The attachment of 

 quartz fibers," Phil. Mag., vol. 37 (1894). 



^ William Watson, "A text-book of practical physics," Longman, Gteen & Co. (581-586). 



