60 SEC. 3. MEASUREMENT. 



233a. Photographs, showing two kinds of machines i'or 

 measuring with great precision the alterations in shape produced 

 in metals by tension and compression. Dumoulin Froment, Paris. 



291. Calliper Apparatus, for accurately determining dia- 

 meters and lengths up to 150 mm. 



A. Meissner (ff. Muller and F. Reinecke), Berlin. 



^L millimeter can be obtained by direct reading by means of a microscope, 

 and the T | 7 part of a millimeter by estimation. 



293. Collection of Timber Callipers for the use of 



foresters. C. Staudinger and Co. (F. W. von Gehren), Giessen. 



A collection of tree-callipers (" Baumkluppen "), mostly in use for the pur- 

 pose of comparison with those of Staudinger's construction, by many autho- 

 rities recognised as the best. A list of the names is added to the collection. 



298. Calliper Compasses, with plane contact lever. 



Physical Institute of the University of Kiel (Prof. Dr. 

 G. Karsteri). 



This appai-atus, which is in the possession of the Physical Science Institute 

 of the University of Kiel, was constructed in 1832 by liepsold, and made use 

 of by Schumacher for comparing the platinum kilogramme of the archives 

 with the Danish. 



(See Schum. Astronom. Jahrbuch, 1836, p. 243.) 9 



A description by G. Karsten of the instrument will be found in " Vom 

 Maasse und vom Messen," vol. I. of the " Encyclopedic der Physik," p. 506 

 and following. 



308. Apparatus for measuring the Thickness of Thin 



Plates. R. Fuess, Berlin. 



308a. Improved Patent Measuring Gauge, with 

 patent releasing arm. Wm. Henry Laidler. 



This gauge is constructed to enter a hole drilled in a plate ; the arm will 

 clear any rough edge or burr, and when the measurement is taken the arm 

 can be released, and the instrument withdrawn, without altering or interfering 

 with the indication. Each division on the vernier shows 1 - 1 00 part of an inch. 



3O8b. Improved Ivory Calliper Gauge, with Engi- 

 neer's Slide combined. Wm. Henry Laidler. 



D. CATHETOMETERS. 



241. Differential Cathetometer, an apparatus designed 

 for measuring variations in the length of solid bodies, particularly 

 of rods and wires. Dr. Heinrich Streintz, University of Gratz. 



The principle on which this apparatus is based is, reading by reflection from 

 two mirrors. Two levers, having small mirrors ss attached to them perpendi- 

 cular to their axis, are turned by the flat ends of the bar to be measured as 

 indicated in the drawing. If a telescope and a scale are placed, at some 

 distance, in such a position that the image of the scale reflected by the mirror 



