320 THE PLEASURE, OR [MARCH 



Thermometer &. Thermometer a. 



20 minutes V 4 "TY" . t- ' 15QO 46 



1 hour 30 " . %= -U 101 45 



2 hours 30 " ^ . .i*V* 80 J 42 



12 " 40 &.;. *,<*;.; y,*sfc- A-i t 45 40 



The mean temperature of the external air to which the box was 

 exposed during the above period was 42, the maximum being 47, 

 and the minimum 37. 



Experiment No. 2. With the same arrangement as in the pre- 

 ceding case, a gallon of boiling water was introduced above the peat 

 and water, when the thermometer a was at 36; in ten minutes it 

 rose to 40. The cock was then turned, for the purpose of drainage, 

 which was but slowly effected, and, at the end of twenty minutes, 

 the thermometer a indicated 40; at twenty -five minutes 42, whilst 

 the thermometer b was 142. At thirty minutes, the cock was 

 withdrawn from the box, and more free egress of water being thus 

 afforded, at thirty-five minutes the flow was no longer continuous, 

 and the thermometer b indicated 48. -The mass was drained and 

 permeable to a fresh supply of water. Accordingly, another gallon 

 of boiling water was poured over it, and, in 



3 minutes, the thermometer a rose to 77 



5 " " " fell to 76J 



15 " " " " 



20 " " " remained at 7l 



1 hour 50 " " " " 70 



In these two experiments, the thermometer at the bottom of the 

 box suddenly rose a few degrees immediately after the hot water was 

 added ; and it might be inferred that heat was carried downwards by 

 the water. But, in reality, the rise was owing to the action of the 

 hot water on the thermometer, and not to its action upon the cold 

 water. To prove this the perpendicular thermometers were removed. 

 The box was filled with peat and water to within three inches of the 

 top ; a horizontal thermometer, a /, having been previously secured 

 through a hole made in the side of the box, by means of a tight- 

 fitting cork, in which the naked stem of the thermometer was grooved. 

 A gallon of boiling water was then added. The thermometer, a very 

 delicate one, was not in the least affected by the boiling water in the 

 top of the box. 



In this experiment, the wooden box may be supposed to be a field; 

 the peat and cold water represent the water-logged portion ; rain falls 

 on the surface, and becomes warmed by contact with the soil, and 

 thus heated descends. But it is stopped by the cold water, and the 

 heat will go no further. But, if the soil is drained, and not water- 

 logged, the warm rain trickles through the crevices of the earth, car- 

 rying to the drain level the high temperature it had gained on the 

 surface, parts with it to the soil as it passes down, and thus produces 

 that bottom heat which is so essential to plants, although so few sus- 

 pect its existence. 



This necessity of warmth at the root undoubtedly explains why it 

 is that hardy trees, over whose roots earth has been heaped, or hav- 

 ing laid, are found to suffer so much, or even to die ; in such case, 



