30 BULLETIN OF THE 



outward ; the required movement in use is less than ^^^th of an 

 inch. The cylinder is filled with oil, and from its centre a pipe 

 leads to a small piston on top of the instrument on the inside of 

 the car. Any pressure on the draw-bar either pulling or pushing^ 

 is transmitted to the piston (which is held by springs of known 

 tension), and thence to arms holding the pen which records the 

 pressure. Inside of the car is a large cast-iron frame, 36 X 40 

 inches, and 30 inches high, which supports the mechanism to roll 

 the paper as the car moves, it being driven by positive gearing 

 from the axle of the car. 



The present Dynagraph uses paper 30 inches wide, though hy 

 leaving off -some of the attachments, paper 20 inches wide can 

 be used: it has gearing to represent 400, 200, 100, or 50 feet of 

 track per inch of paper, as desired : strong Manilla paper, spe- 

 cially made, is used, and is w^ound in a continuous sheet of 400 

 to 500 feet in length on one of the paper drums at either end of 

 the instrument. These drums are driven by friction and only 

 serve to wind the paper, keeping it taut as it is fed through the 

 machine by the steel rolls, either pair being used according to 

 the direction which the car is running. The rolls make 1/g- 

 revolutions for 13/o inches of paper; this corresponds to 400 

 feet of track for 1 inch of paper. The rolls are xinr^ of ^^ ii^ch 

 larger in diameter in the centre than at the eiids. 



The wheels which drive the mechanism are turned without any 

 conning, and are 33 inches in diameter. A triple thread worm 

 on the axle drives a shaft which is connected by three universal 

 joints with the shafting of the instrument. There are three mitre 

 gears so arranged with saw-tooth clutches that the paper can 

 run in either direction, and either pair of feed rolls, also used 

 at pleasure. Right or left-handed diagrams can be taken, as- 

 desired. There is an integrating attachment which measures^ 

 constant areas of the dynamical curve and records them electric- 

 ally. The electrical recording apparatus has 11 pens: one re- 

 cords from the clock seconds ; one every tenth second, and one 

 for each minute ; one pen records the constant area on the dia- 

 gram ; one pen the amount of water (as measured by a meter) 

 used by the locomotive, and where consumed ; one pen the amount 

 of coal, and its distribution ; one pen the alignment of the road ; 

 one pen the distance as measured by the instrument; one pen the 

 revolution of the drivers; one pen the velocity of the wind/and 

 one pen the roads, mile posts, and stations. 



In special experiments on trains all the pens are used as de- 

 scribed, but some of them may be used for other purposes if 

 desired. In making experiments on single cars we have inside 

 the larger pistons, smaller ones, so that the same springs give 

 five times as large a scale as with the large pistons. 



Among the many important uses of the Dynagraph has been 

 the determination of the effect of different classes of locomotive 

 wheel bases upon the wear of rails and tires of the driving wheels. 



