92 BULLETIN 173, U. S. NATIONAL MUSEUM 



marker indicating speed is actuated by a spring-balanced bellows, 

 the motion of which is determined by the volume of air delivered to 

 it by small air-pump cylinders actuated by any convenient part of 

 the engine. The other markers are actuated mechanically by a 

 series of levers to various indicating instruments on the engine, 

 not described. 



RICHARDS INDICATOR, c. 1867 



Pi^\TE 20, Figure 2 



U.S.N.M. no. 307515 ; original ; gift of tlie Ball Engine Co. ; photograph no. 

 15260A (group). 



This is the type of "high speed" steam-engine indicator patented 

 by Prof. C. B. Richards in 1863 (Patent no. 37980) and introduced 

 commercially about 1867. 



This is considered the first design of the modern type of indica- 

 tor. It was the first to employ a multiplying linkage between the 

 piston and the pencil point to reduce the travel of the piston and 

 so avoid the distortion of the diagram due to the inertia of the 

 moving parts. It has a cylinder liner supported so that it is free 

 to expand and contract longitudinally with temperature changes, 

 and it provides a means of moving the pencil into and away from 

 contact with the paper. 



The pencil mechanism is a Watt parallel motion that moves the 

 pencil parallel with the piston, coincident with it and in an exact 

 ratio of travel. It multiplies the movement of the piston about 

 four times. The parallel motion is supported by two arms that 

 are a part of a collar that is fitted so that it may be turned about 

 the top of the cylinder to bring the pencil into contact with the 

 paper. The indicator spring is a heavy, single-coil, helical spring 

 fitted with threaded collars by which it is attached to the piston 

 and the cylinder cap. It is easily removable so that lighter or 

 heavier springs may be substituted. 



G. H. CROSBY INDICATOR, 1879 



Plate 20, Figurk 3 



U.S.N.M. no. 308701; original patent model; transferred from the United States 

 Patent Office; photograph no. 15260A (group). 



This indicator was filed with the application for Patent no. 219149 

 issued to G. H. Crosby, September 2, 1879. 



The improvements claimed for this design are a jacket about the 

 steam cylinder to prevent radiation or loss of heat from the cylinder ; 

 a method of supporting the cylinder and jacket so that each might 

 expand freely when heated; the carrying of the rotary drum on 

 a lever so that it could be moved up to and away from the marker; 



