MEASUREMENT OF GROWTH 



289 



of a small bit of ignited camphor until the paper is covered 

 with an even layer of soot. Adjust in place again and set the 

 clockwork in action, so that the cylinder will be given a partial 

 turn every hour. The growth of the organ will allow the short 

 arm of the lever to rise a distance equal to the amount of 

 elongation, and the long arm to fall six times this 'amount, if that 

 proportion has been established between the two arms of the 

 lever. The gradual descent of the lever will trace a straight line 

 in the soot on the paper showing the multiplied growth during 

 the hour : at the end of that period the clock releases a clutch 



TJ 



FIG. 138. Thermograph. 



and allows a weight to turn the cylinder a short distance during 

 which movement the point of the lever traces a straight horizontal 

 line. The process is repeated every hour and when the lever has 

 reached the lower end of the cylinder it will have made a line 

 resembling the section of a set of stair steps, of which the vertical 

 lines represent multiplied growth, and the horizontal lines the 

 hours. Shorten the thread and thus raise the tip of the lever to 

 its former level and allow it to trace another line : repeat in such 

 manner as to secure a record for several days if possible. Set a 

 thermograph near the instrument and secure a continuous record 

 of the temperature also. 



