280 SOWING. 
temperature has a very decided influence upon 
the time required for germination, and that, 
within certain limits, the higher the tempera- 
ture is the more rapidly does the process go on. 
But it must be kept in mind, that soil receives 
its heat through the medium of the air, and that, 
consequently, the surface is always more quickly 
heated than that deeper down. In fact, the heat 
progresses so slowly from above downwards, that 
it has been found that at a certain depth beneath 
the surface, the temperature of summer is not 
felt until the following winter. Whenever the 
air is warmer than the soil, the surface of the 
soil will be warmer than that below the surface ; 
when, on the other hand, the air is cooler, the 
surface of the soil will, by contact, cool much 
more rapidly than that below the surface. From 
this state of matters it follows, that the most 
rapid germination will occur at about 1 inch or 
SOWING-MACHINES. 
so below the surface, to which depth the heat 
will soon penetrate, and which, nevertheless, will 
not be so readily cooled during the night. On 
this account, the seeds at this level will generally 
grow most rapidly, and the germination of others 
will occupy more and more time, as the distance 
between them and the surface is increased. It 
is owing to this fact that seeds too deep sown do 
not grow at all, the temperature not being suffi- 
ciently elevated, and the supply of air too limited 
to set the chemical processes at work which are 
essential to germination. In fig. 7, we perceive 
this result very clearly demonstrated ; for, while 
the plants at one spot, where the seeds were 
about 1 inch below the surface, have attained a 
good size, those which slipped down between 
the furrow-slices from the bad ploughing, have 
scarcely yet appeared above ground, as below a 
and 6 of jig. 6. Turning your attention to jig. 8. 
Fig. 8. 
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you will at once perceive the immense advan- 
tage of the machine over the hand-sown crop. 
In this case, you can work up your land to any 
degree of fineness you please, by harrowing, 
grubbing, rolling, &c. You are preserved from 
every injury arising from a careless distribution 
of the seed; and even the errors of your plough- 
men have not so serious an effect upon the result 
of the crop. The machine delivers the seed, as 
in the upper figure, with the greatest exactness, 
at any depth you please, and the result is, as 
shown in the lower figure, the greatest equality 
in the braird.” 
SOWING-MACHINES. Implements for the 
easy and regular distribution of seeds alone or of 
seeds and special manures. They did not ac- 
quire a very refined character till a comparative- 
ly recent period, and they are still unused, in 
even their rude state, in some of the remote and 
least improved districts of Britain; yet they 
have been known for centuries in both the ex- 
treme east and the extreme west of the civilized 
world, and have, for a long period, been progres- 
sively multiplied in form and kind, and anxious- 
ly studied and improved by some of the ablest 
agricultural mechanicians. The farmers of China, 
India, Japan, and Arabia have, from time im- 
memorial, drilled and dibbled in their seeds. 
The Chinese sowing-machine of the present day 
resembles in some respects a hand-barrow and in 
others a small plough, and has three hollow teeth 
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of about 28 inches in length with iron supports, 
and carries the seeds in a box above the wheels, 
and drops them thence through the teeth to the 
ground, in rows of from 7 to 14 inches distant ; 
and it follows the plough, and is itself followed 
by a small wooden roller, which covers the seeds 
and supplies the place of a harrow. The Hindoos, 
after depositing the seed in a similar way, use a 
kind of subsoil plough, which loosens the soil, 
three drills’ breadth at a time, to the depth of 
about 8 inches. About the middle of the 17th 
century, Gabriel Platte described a rude dibbling 
machine, which was formed of iron pins “ made 
to play up and down like Virginal jacks ;” and 
about twenty years later, Worlidge published an 
account of a seed and manure drill of his own 
invention, and Evelyn strongly recommended to 
the attention of Englishmen the sembrador drill- 
plough which had been invented on the Conti- 
nent. See the article Semprapor. At the intro- 
duction of the drill husbandry under Jethro 
Tull, that great improver first attempted to re- 
vive attention to the sembrador, and next in- 
vented sowing machines of his own, and endeay- 
oured to render them fully subservient to his 
system, “ His first invention was a drill-plough 
to sow wheat and turnip seed in drills three rows 
at atime. There were two boxes for the seed ; 
and these, with the coulters, were placed one set 
behind the other, so that two sorts of seed might 
be sown at the same time. A harrow to cover 
