Sir yagadis Bose 31 



a delicately poised system of compound levers, but friction 

 of contact at the bearings limited magnification to ten 

 thousand times, which was not sufficient for his purpose. 

 Then he tried a single magnetic lever, which by its move- 

 ment rotated a delicately poised astatic needle (a needle 

 which is unaffected by the earth's rotation). A spot of 

 light reflected on a screen from a tiny mirror attached to 

 the needle gave a magnification which could be increased 

 from a million to a hundred million times. This magnified 

 the highest power of a microscope no less than one hun- 

 dred thousand times. He called this machine the cresco- 

 graph (growth-recording machine), and some idea of its 

 power may be gathered from the fact that if attached to 

 a snail it would show this slowest of creatures as shooting 

 forward at the rate of two hundred million feet an hour. 

 Sir Jagadis says : 



Plants have hearts. Long before I invented the crescograph 

 I was already certain that sap-pressure rising in the stem worked 

 in almost exactly the same way as blood driven by the human 

 heart. In other words the pressure was not constant, but came 

 in beats. The crescograph gave definite proof that every sur- 

 mise was correct. The actual rate of the pulsation of sap in a 

 cyclamen proved to be the one-hundred-thousandth part of an 

 inch per second, but when the leaf was placed on the magnetic 

 needle of the instrument the spot of light curved to and fro on 

 the screen at the rate of ten feet in twelve seconds. 



Another method employed by the great Indian scientist 

 was one in which he pushed an electrical probe against the 

 stem of the plant, shifting the probe forward by one-tenth 

 of a millimetre at a time until the galvanometer began to 

 record. His aim was to keep the stem stationary, allow- 

 ing the rod to touch the stem with just the right pressure, 

 so that each heart-beat could be discovered. The great 

 difficulty was to find the right kind of rod ; many things 

 were tried, but proved useless. One day Sir Jagadis was 



