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Sir J. C. Bose and Mr. G. Das. 



1. Method of High Magnification. 



The practical difficulties met with in carrying out this idea are very 

 numerous. It will be understood that just as the imperceptible movement 

 is highly magnified by the compound system of levers, the various errors and 

 difficulties are likely to be magnified in the same proportion. The principal 

 difficulties met with were due : (1) to the weight of the compound lever, 

 which exerted a great tension on the growing plant ; (2) to the yielding of 

 flexible connections by which the plant was attached to the first lever, and 

 the first lever to the second ; and (3) to the friction at the fulcrums. 



Weight of the Lever. — As the first lever is to exert a pull on the second, it 

 has to be made rigid. The second lever serves as an index, and can 

 therefore be made of fine glass fibre. To secure rigidity of the first lever 

 large cross-section and consequent weight is required, which exerts consider- 

 able tension on the plant. Excessive tension greatly modifies growth ; even 

 the weight of the index vised in self-recording auxanometers is found to retard 

 the normal rate of growth. The weight of the levers introduces an 

 additional difficulty in the increased friction at the fulcrums on account of 

 which there is an obstruction of the free movement of the recording arm of 

 the lever. The conditions essential for overcoming the various difficulties 

 are therefore : (1) construction of a very light lever possessing sufficient 

 rigidity, and (2) arranging the levers in such a way that the tension on the 

 plant may be reduced to any extent, or even eliminated. 



I found in " navaldum," an alloy of aluminium, a light material possessing 

 sufficient rigidity. The lever is constructed out of a thin narrow sheet 

 25 cm. in length. The first lever has, as explained, before, to be fairly rigid 

 in order to exert a pull on the second without undergoing any. bending ; this 

 rigidity is secured by giving the thin narrow plate of the lever a T-shape. 

 The first lever balances, to a certain extent, the second. Finer adjustments 

 are made by means of an adjustable counterpoise B, at the end of the levers. 

 By this means the tension on the plant can be greatly reduced, or a constant 

 tension may be exerted by means of weight T (fig. 1). In my later type of 

 apparatus the plant-connection is made to the right instead of the left side 

 of the first fulcrum. This gives certain practical advantages. The second 

 lever is then made practically to balance the first, only a very slight weight 

 being necessary for exact counterpoise. The reduction of total weight thus 

 secured reduces materially the friction at the fulcrum, with great enhance- 

 ment of efficiency of the apparatus. 



The recording lever has a normal excursion through 8 cm. on the 

 recording surface, which is a very thin sheet of glass 8x8 cm., coated with a 



