INK-RECORD 2$ 



the successive strokes occurred at intervals of thirty-five 

 seconds ; at the end of twelve hours the frequency was 

 found to be unchanged. After twenty-four hours the coiled 

 spring was nearly unwound ; even in this extreme case the 

 interval between successive strokes was found lengthened 

 from 35 to 35-5 seconds, i.e. a variation of only i-i per 

 cent. 



The maximum variation of the speed of the drum is, 

 as already stated, about ten times. The circumference 

 of the drum is 30 cm. ; when the drum revolves once in 

 six minutes, the rate of movement of the recording surface 

 is 50 mm. per minute ; the slowest speed is one revolution 

 in sixty minutes, the movement of the recording paper being- 

 no w 5 mm. per mmute. We can easily obtain any inter- 

 mediate speed between these two extremes. 



The Electromagnetic Writer is mounted on a sliding 

 tube, and after the completion of the record, during one 

 complete revolution of the drum, it can be moved through 

 one cm. to make a new record. It is thus possible to obtain 

 a continuous record for ten hours, as in the case of an 

 investigation on the diurnal variation of photosynthesis 



Ink-Record. — The record on a drum is usually obtained 

 by inscription on a piece of smoked paper. But coating 

 the paper with smoke and the subsequent fixation of the 

 record entail much trouble. I have simplified the process 

 by arranging for a direct record with ink on white paper. 

 A lever carries at one end a small spherical vessel, with 

 a narrow tube filled with aniline ink ; the tube is nearly 

 closed by a thin wire which projects slightly beyond the tube, 

 so that the ink is prevented from dripping : this is the pen 

 (fig. 3, 1). The armature of the electromagnet is attached 

 to the arm of the lever which carries the pen ; the other 

 arm is kept down by a light spring, so adjusted that the 

 point of the pen is held 2 mm. above the recording-surface. 

 The completion of the electric circuit on the escape of each 

 bubble causes the pen to come into contact with and to 

 make an ink-mark on the recording surface. 



