VARIATION OF TEMPERATURE 



35 



thermal regulator. The rate of heating or cooling of the 

 regulator depends on the rate of inflow of hot or cold water. 

 To effect a gradual rise of temperature in the plant-chamber, 

 the stopcock Si is first opened. The experimenter, keeping 

 his hand on the stopcock S3, then carefully adjusts the 

 rate of inflow ; he has before him a clock-hand which goes 

 round once in a minute, and with previous practice he is 

 able to adjust the inflow, so that the rate of rise of tempera- 

 ture of the plant-chamber, indicated by the thermometer T, 



Fig. 14. Arrangement for variation of temperature of plant- 

 chamber. 



p, plant-chamber enclosed in thermal regulator t.r. ; h and c, 

 reservoirs containing hot and cold water. Variation of 

 temperature of thermal regulator adjusted by proper 

 manipulation of stopcocks s^, Sg, and s^, Sg. o, outflow pipe. 

 Plant attached to recording lever w. "t, thermometer. 



is half a degree every 30 seconds or one degree every 

 minute. The mass of water in the thermal regulator 

 acts as a stabihser, preventing any sudden fluctuation of 

 temperature. A similar method is also employed for the 

 gradual lowering of temperature. The adoption of this 

 device for ensuring gradual variation of temperature was 

 found to eliminate the erratic changes in the rate of growth 

 which had previously proved to be so extremely baffling. 



