40 MOVEMENT 



How a Moving Body can record its Own Movement. — 

 Poncelet and Morin solved this problem by construct- 

 ing the well-known machine which registers the 

 movement of a falling body. In this machine, the 

 falling body is provided with a needle, which leaves 

 its record on paper, and moves in a vertical direction at 

 the same rate as the falling body. Further, the paper 

 rolled round a revolving cylinder advances in a hori- 

 zontal direction at a uniform rate. When the paper 

 is taken off the cylinder, the needle is found to have 

 traced a curve which is parabolic in form. This is the 

 geometrical manner of expressing a movement of 

 uniform acceleration. This machine is a type of the 

 recording apparatuses of which there are nowadays a 

 considerable number. It must be mentioned at the 

 same time that, by reason of its construction, it can 

 only record the curves of movement to actual scale ; it 

 could not, therefore, be used to represent movements 

 too small or too extensive to be inscribed on a sheet of 

 paper. It follows that, in order to bring the propor- 

 tions of the movement, the curve of which is to be 

 recorded, within convenient proportions, it must either 

 be enlarged or reduced. 



Proportional Enlargement and Reduction of the Re- 

 corded Movement. — Very feeble movements, such as 

 occur in living organs, and such as physiologists wish 

 to understand, usually have to be immensely enlarged. 

 This can be effected by levers with needles fixed to 



lias traversed a distance of five hectometres at a uniform rate. 

 This rate is maintained for two minutes longer (section B), then 

 a stoppage occurs for one minute, after which the moving hody 

 again advances at an accelerated pace until the tenth minute. This 

 speed of two hectometres a minute is maintained up till the end 

 of the eleventh minute, when it again gives place to a slower move- 

 ment of three hectometres in four minutes. This is maintained 

 during section D and part of E, until the twenty-first minute, at which 

 a period of rest occurs. This stop of three minutes, which is continued 

 during section F, is followed by another period of uniform movement 

 during which the speed is a little more than 100 metres per minute. 



