34 
Jethro Tail: his Life, Times, and Teacliing. 
air; dew has both of these substances. The chemistry of 1732 
did not enable him to distinguish between nitre and nitric acid — 
aquafortis — but he did distinguish ' an acid spirit in the air,' 
and ' much of the nature of aquafortis.' Here he was giant 
strides in advance in the knowledge of his day." 
Dews, he thinks, are exhaled from rivers and moist lands, 
and from the expirations of vegetables. Dew is re-exhaled from 
waste ground, but most of that which falls on well-tilled land is 
retained. He well knew that rain-water contains foreign sub- 
stances. Could we compute the quantity of earth — in his mind 
the food of plants — in rain-water, it might correspond to the 
quantity of earth — food of plants — taken off' annually by the 
wheat. Tull experimented on roots with a view to ascertain 
how they absorb food ; he placed plants of mint in plain water, 
salt and water, and partly in both salt and fresh water. Some 
he placed partly in milk, others in a strong infusion of garlic, 
with other constantly varied experiments, and noted the effects 
for his practical object. 
The gases in his day were all confounded under the name 
of air ; he was aware, however, that air passes into the leaves of 
plants, and that without air plants die. Enthusiasm in regard' 
to tillage made Tull appear, as has been observed, to run a-muck 
against farm-yard dung, which, no doubt, with poorly fed animals, 
in Tull's day, was poor stuff; twenty to thirty loads per acre were 
constantly used. He appreciated hand manures, especially peat 
ashes, which he carted twelve miles. He had a considerable 
knowledge in regard to capillary attraction, and the absorptive 
power of finely pulverised earth. 
Tull drilled his turnips in six-feet ridges, sometimes in a 
single, sometimes in a double row, fourteen inches apart, and 
used dung; " it is useful, for turnips have commonly less time 
to grow than other plants." He pleaded earnestly for wide 
intervals between the ridges of wheat, to be horse-hoed. Tull's 
system, as to pickling wheat, is, in many parts of the country, 
followed to this day. He was also well aware of the importance 
of change of seed ; flax-seed, he says, " brought from Holland 
and sown in England will bring as fine flax as there, but the 
very next generation is coarser." 
Tull, according to Wren Hoskyns, did not push his tlieory 
far enough : where his theory halted his practice began to fail.- 
He did not know the object of stirring was to admit freely air 
and water, which contain all the organic elements of vegetation — 
hydrogen, carbon, and anmionia. Had he known this he would 
have avoided the erroneous theory which led to his want of due 
appreciation of the chemical value of manure as opposed to its 
