MAGNETIC CRESCOGRAPH I9 



record of a single pulse of growth obtained with the peduncle 

 of Zephyranthes sidphiirea (fig. 8). The magnification 

 employed was 10,000 times, the successive dots being at 

 intervals of i second. It will be seen that the growth-pulse 

 commenced with a sudden elongation, the maximum rate 

 being -4 [jl per second. The pulse of elongation exhausted 

 itself in the course of 15 seconds, after which there was a 

 partial recovery lasting for 13 seconds, the period of the 

 complete pulsation being 28 seconds. The resultant growth 

 is therefore the difference between the elongation and the 

 recovery. Had not a very highly magnifying arrangement 

 been used, the growth w^ould have appeared to be continu- 

 ous; this is especially the case when the rate is very high. 

 Less favourable conditions appear to promote exhibition 

 of the pulsation, instances of which will be described later. 



The Magnetic Crescograph 



The highest magnification obtained with two levers is, 

 as already stated, 10,000 times. It might be thought that 

 further magnification would be possible by a compound 

 system of three levers. There is, however, a practical 

 limit to the number of levers that can be employed. The 

 slight overweight of the last lever becomes greatly multi- 

 plied, exerting considerable tension on the plant and thus 

 interfering with the normal rate of growth. The friction 

 at the bearings also becomes increased, obstructing the free 

 movement of the writing lever. For securing further 

 magnification, the idea of more material contacts had 

 to be abandoned. A method of magnification without 

 additional contact had therefore to be devised. A 

 magnetised rod of steel was made to function as the first 

 lever, the magnified movement of which causes a very large 

 deflection of a delicately suspended astatic system of 

 magnets. The indicator is a spot of light reflected from 

 a mirror carried by the deflected astatic system. The 

 magnetic lever itself gives a magnification of 50 times, and 



