i8 RESEARCHES ON IRRITABILITY OF PLANTS 



a clock or a phonograph motor, according to what may 

 be the requirement of the speed. The quarter-plate size 

 (n X 8 cm.) is convenient for record, as it is not too large 

 for book illustration. The suspending thread passing over 

 pulleys is wound round the winding- wheel of the clock. This 

 wheel is provided with click and ratchet, which allow it to 

 be wound without interfering with the axis of the clock. 

 Thus winding of the wheel in the left-handed direction pulls 

 up the recording-slide. The running-down of the clock then 

 allows the slide to fall at a uniform rate. The various 

 speeds found necessary for different records were such that 

 the entire length of the plate, n cm., travelled past the 

 recording-point in .5 second, 6 seconds, 15 minutes, 1 hour, 

 or 3 hours. The first two of these rates were obtained from 

 a phonograph motor employing two different-sized wheels. 

 The last three were obtained by attaching three different- 

 sized wheels to the clock-axis which carries the minute-hand. 

 In these slow rates the movement of the plate is quite uniform 

 from the beginning, but when, as in the first two cases, this 

 has to be dropped at a relatively high speed, a short time 

 will elapse, equivalent at most to the first fourth of the 

 plate, before it becomes quite uniform. Should uniformity 

 of such movement be specially desired for the record, it must 

 be commenced after passing this first fourth. But on account 

 of the chronographic signals which accompany the record, 

 this uniformity is not absolutely essential, for they give 

 us the data from which the time-relations of the curve 

 may be derived. 



I may here refer to a few practical points with regard 

 to the preparation of the glass for record and its subse- 

 quent fixing. In order to produce an even layer of smoke 

 on the recording-plate, it is moved over the gas-flame 

 from a bat's- wing burner ; and this deposit of smoke will 

 be improved if the gas has been previously passed through 

 a jar containing a small quantity of benzine. After the 

 record is taken, it is fixed by pouring carefully over 

 it a dilute solution of Canada balsam in xylol. It is 



