(RESPONSE TO WIRELESS STIMULATION 173 

 by a slight diminution of daylight, which is hardly 

 noticed by a human observer. 



Bose also found that the growth of plants was affected 

 by changes in the environment which were below the limit 

 of human perception. For this new range of investigation 

 he had to turn his attention to a new type of apparatus, 

 the sensitiveness of which had to surpass those which he 

 had already invented. The High Magnification and the 

 Magnetic Crescograph enabled him to measure the most 

 minute rate of growth. For the detection of the effect of 

 impact of external stimulus, he had first to measure the 

 normal rate, and afterwards the changed rate induced by 

 the stimulus. The effect of stimulus, whether stimulating 

 or depressing, could be found from calculation of the 

 difference in the two cases. He now wished to eliminate 

 the necessity for calculation and the consequent loss of 

 time. The idea that now possessed him was to devise a 

 new method which would instantly show by the up or down 

 movement of an indicator the accelerating or retarding 

 effect of the agent on growth. 



The desideratum was to compensate the up-movement 

 of growth by some regulating device ; this involved the 

 problem of making the plant descend at the exact rate at 

 which the growing tip of the plant was rising, whatever that 

 rate may be. Some such regulator has to be introduced as 

 in the compensating movement of an astronomical telescope, 

 by which the effect of earth's movement round her axis once 

 in twenty-four hours is neutralised. But the problem that 

 confronted Bose was far more difficult, for instead of com- 

 pensating a definite rate he had to obtain adjustment for 

 widely varying rates of growth in different plants, and even 

 of the same plant under different conditions. 



The difficult problem was successfully solved in his 

 Balanced Crescograph (Fig. 19). A train of revolving clock- 

 wheels, actuated by the fall of a weight, lowers the plant 

 exactly at the same rate at which it is growing. The exact 

 adjustment is obtained by the gradual turning of a screw 



