252 ABSORPTION OF HEAT BY LEAVES 



to red heat. The thermometer used was one of 

 Fahrenheit, graduated only to the boiling point ; 

 I could not obtain one graduated higher, or one 

 the bulb of which could be laid bare. On ap- 

 proaching the bulb of the thermometer carefully, 

 and placing it against the inner part of the iron 

 vessel, but remote from the centre or part most 

 heated, the mercury rose instantaneously to the 

 utmost range, so that I was obliged immediately 

 to withdraw it. This example may be sufficient 

 to mark the high temperature to which the vessel 

 was raised. After the first roasting I placed as 

 quickly as possible the thermometer in the parcel 

 of leaves about to be rolled, and slightly pressed 

 them against the bulb. The mercury rose only 

 to 138 degrees. I repeated the experiment with 

 another parcel of leaves in the same manner, and 

 the temperature indicated was 136°. After the 

 second roasting of the same leaves the thermometer 

 rose only to 132°. This lower temperature, how- 

 ever, I consider as accidental; some allowance must 

 of course be made for loss of heat in carrying 

 the leaves from the roasting vessel. Still on a 

 recent occasion, I roasted some hawthorn leaves 

 at a temperature of 270°, and another thermometer 

 was kept above the boiling point in readiness for 

 use. At an agreed signal I raised the leaves from 

 the vessel, and an assistant immediately thrust the 

 heated thermometer into the leaves, which I gently 

 pressed against the bare bulb. The thermometer 



