94 BULLETIN 173, U. S. NATIONAL MUSEUM 



The exact strength of spring is obtained by screwing the spring 

 into the head more or less, when they are firmly fixed. The foot 

 of the spring is a small steel bead firmly pinned to the straight por- 

 tion of wire at the bottom of the spring. This takes the place of 

 the heavier brass foot used in earlier indicators. 



INDICATOR WITH CONTINUOUS CARD APPLIANCE, 1930 

 Plate 20, Figube 4 



U.S.N.M. no. 309834; original; gift of the Crosby Steam Gage & Valve Co.; 

 photograph no. 18547A. 



In this indicator the piston spring is located outside of the cylinder 

 casing in a position above the moving parts, where it is not affected 

 by the heat of the steam ; and the piston is made in the shape of the 

 central zone of a sphere to reduce the friction caused by possible 

 eccentricity in the action of the spring. The ordinary drum of the 

 indicator has been displaced by an appliance for taking a continuous 

 series of diagrams of the successive strokes of an engine. 



The piston is attached by a hollow rod directly to the upper end 

 of the spring and because of its spherical shape moves freely in spite 

 of any eccentric action of the spring. The bearing of the spherical 

 piston on the cylinder wall approaches line contact, so that friction 

 is greatly reduced. 



The Lanza continuous diagram appliance is assembled on a bracket 

 that displaces the usual paper drum and supports the indicator 

 proper. It consists of a spindle for receiving the new roll of paper, 

 the drum that feeds the paper forward and upon which the pencil 

 point bears in making the record, and the spool upon which the 

 paper is afterward wound. 



The drum is rotated continuously in one direction by the alternate 

 engagement of two clutches controlled by a cord passing over the 

 pulley at the extreme end of the bracket arm and actuated by a cross- 

 head block positively connected to the crosshead of the engine. There 

 is included a device for marking upon the paper at the end of the 

 stroke and an atmospheric marker readily adjustable to any required 

 position. 



This appliance is the invention of the late Prof. Gaetano Lanza, 

 of the Massachusetts Institute of Technology. It is used to obtain a 

 continuous series of cards from locomotives, rolling mills, and other 

 engines where the diagrams corresponding to successive revolutions 

 of an engine differ. 



