10 On Harrowing W heat. 
produce the vegetable fermentation ; besides this crust 
or cake by being completely deprived of its aqueous 
particles, become more contracted than the stratum im- 
mediately under it, hence it becomes divided by innu- 
merable cracks or openings, into which multitudes of 
insects enter and find safe lodgings under the hard 
crust, where they remain secure from the scorching 
rays of the sun &c. through the day, and come up 
through the cracks or openings at night, to prey upon 
the tender plants, and return to their lodgements when 
the sun begins to be troublesome in the morning. But 
by passing a light harrow over the grain in the spring, 
as soon as the ground is so much hardened as to bear 
the horses feet without sinking, the young plants are 
relieved from that unnatural pressure, a free access is 
given to the light, and air to the roots; by stirrmg up 
the soil a new fermentation is produced, and the little 
insects are dislodged from their subterranean habita- 
tions, all their operations disconcerted, and they left 
to perish by the influence of the sun and weather. By 
this operation the grain in a few days acquires a fresh 
vigour, equal if not superior to what might be pro- 
duced by a top dressing. 
This writer likewise expatiates upon the great advan- 
tage of harrowing summer fallows after every plough- 
ing, by which he says one half the ploughings may be 
saved, and the intention of the operation much better 
effected. He observes that if the soil derives any rich- 
ness from the atmosphere it must be while it is ina 
state of fermentation, and harrowing is the best means 
for producing that effect; besides the seeds of annual 
weeds cannot be destroyed till they first vegetate, but 
