II. LENGTH. 59 



267d. Apparatus for Measuring the Length of the 

 Impressions made by the Rodman Scale. 



Technological Institute at St. Petersburg. 



The copper plate, on which is the impression to be measured, is placed on 

 the slide of the apparatus, and then one end of the impression after the other 

 is brought under the cross thread of the microscope by means of the screw of 

 the slide, when the reading can be made on the head of the screw. By- 

 means of a micrometer eyepiece also smaller dimensions can be measured. 



The apparatus belongs to the Technological Institute at St. Petersburg. 



267e. Micrometer for Guns and Tubular Objects. 



Samuel B. Allport. 



This is a tube, provided with three spring arms, radially disposed round its 

 end, between which a cone is inserted. The cone is connected with a screw 

 at the other end of the tube, whereby it is projected or withdrawn, and so con- 

 tracts or expands the spring arms. 



The angle of the cone bears such a relation to the pitch of the screw tha 4 

 the expansion or contraction of the arms when inserted in a tube will indicate 

 the variations in its bore in thousandths of an inch by suitable divisions on 

 the head of the screw. 



267e. Apparatus for measuring the eccentricity of the pivots 

 of a polar or transit axis, with an approximation of * 00001 inch. 



A. Hilger. 



271. Calliper, with Dial, of the English inch measure, 

 divided into eighths. M. Isvardfils. 



272. Calliper, with Dial of two centimetres, divided into 

 tenths of a millimetre." M. Isvardjfils. 



283. Cylindrical Gauges differing in diameter by one ten 

 thousandth of an inch. Other gauges and specimens of surfaces. 



Royal School of Mines. 



284. Universal Calliper, with slide and reverse action. 

 Geneva Association for the Construction of Scientific In- 

 struments. 



Instrument of measurement, for ascertaining equally the thickness, the 

 inner diameter, and length of tubes. 



286. Apparatus for measuring accurately the Diameter 

 of Wires, for testing whether pivots and other turned objects are 

 perfectly circular in form, and for the determination of the error 

 when they are not truly circular. 



Landsberg and Wolpers, Hanover, 



287. Apparatus for measuring the Thickness of thin 

 metal plates, sheets of paper, &c. 



Landsberg and Wolpers. Hanover. 



288. Calliper-Compasses for larger measurements. 



Landsberg and Wolpers, Hanover. 



