ig6 LIFE AND WORK OF SIR JAGAD1S C. BOSE 



since the flowers are already open at night. Finding that 

 light exerted little or no effect, Bose turned his attention 

 to the action of daily variation of temperature. 



We may next enquire whether the daily variation of tempera- 

 ture has any effect in producing the alternate movement of 

 opening and closing of the lily. If the curve of movement of the 

 flower resembled the curve of variation of temperature, we 

 should then have no hesitation in ascribing the floral movement 

 to diurnal change of temperature. In the determination of the 

 influence of temperature on the movement of the flower it is 

 therefore necessary to obtain a diurnal record of the movement 

 of the petal, and also that of the change of temperature through- 

 out the 24 hours. 



The automatic recorder should thus fulfil two different 

 requirements. It should, in the first place, record the magnified 

 movement of the petal, and indicate the time when such move- 

 ment took place ; it should also trace the fluctuation of tempera- 

 ture, both the rise and fall, throughout day and night. For 

 obtaining magnification of movement, one of the petals of the 

 flower is attached by a fine thread to the arm of a light lever 

 made of fine aluminium wire. The lever is supported on jewel 

 bearings which reduce the friction to a minimum. The tip of the 

 longer arm of the lever is bent so as to serve as a writing point. 

 This traces the magnified record of the movement of the petal 

 on a smoked piece of glass, which is moved by clockwork through 

 its entire length in 24 hours. The tip of the writer rubs off the 

 smoke where it touches, and thus leaves a white line on a dark 

 background. The difficulty met here is that there is a consider- 

 able friction at the point of contact of the writer with the glass 

 plate. The free movement of the flower is thus greatly ham- 

 pered and the record thus becomes distorted. This difficulty is 

 overcome by keeping the glass plate, for a greater part of the 

 time, away from contact with the writing point. By a special 

 contrivance of clockwork, the plate is made to approach the 

 writing point intermittently, say once every fifteen minutes. 

 The successive dots thus record the movement of the leaf during 

 successive quarters of an hour during day and night. 



There now remains the method of recording the diurnal 

 variation of temperature. For this I use the simple device 

 of a compound strip, made of the more expansible strip 

 of brass, soldered to the less expansible strip of steel. 



