400 
THE INSTRUCTION OF FARMERS* SONS 
He says, “ A soil of good apparent texture from Lincolnshire 
was put into my hands by Sir Joseph Banks, as remarkable for 
sterility. On examining it, I found that it contained sulphate of 
iron, and I offered the obvious remedy of top-dressing with lime, 
which converts the sulphate into a manure.” 
Now, what is the process by which, as we may suppose, Sir 
Humphrey Davy arrived at the knowledge that the difference 
between this barren soil and other soils of the same appearance, 
consisted in its containing sulphate of iron. By previous in¬ 
struction, he had made himself acquainted w 7 ith the nature of 
soils in general, and with their most usual ingredients, and lie 
proceeded to test for them, one after another, until lie threw in 
the reagent, which forced the latent mischief to shew itself’. 
What can be easier to observe, whether an infusion of anv 
. * . «/ 
kind turns vegetable blues red or not ? But if it does, the infu¬ 
sion contains an acid, and therefore lime, or any alkaline sub¬ 
stance, is a good dressing for it. 
When a piece of paper, moistened with muriatic acid, and 
held over the steam arising from a dunghill, gives out dense 
fumes, it is a certain proof that the decomposition is going too 
far, for it indicates that volatile alkali is disengaged. 
It requires very little labour to observe, whether a soil effer¬ 
vesces by the action of an acid, or whether it burns when heated, 
or what weight is lost by heat; and yet these simple indications 
may convey most valuable information concerning the ingredients 
of the soil. 
If the whole case rested upon these instances, there w r ou d be 
little room to fear refutation ; for they surely prove the applica¬ 
bility of chemistry to agriculture—they prove that many of the 
causes of sterility, and consequently the appropriate remedies, 
may be discovered by its aid. 
Entomology—the Ktiow/edge of Insects .—The first step in 
proof of the utility of this science might be to shew that insects 
do a great deal of harm ; but I shall probably be allowed to 
take that for granted. The destruction of the turnip-crop alone 
is a very serious national evil. Slugs, grubs, and wireworms eat 
the seed in the ground, and other creeping things in the gra¬ 
nary. Flies torment the domestic animals whilst alive, and blow 
their flesh when dead. Caterpillars eat cabbages; and moths 
riddle holes in cloth. Almost every plant has its insect enemy. 
Clover-seed is destroyed by a small weevil (ApionJlavifemora- 
tum) ; Dutch clover by the Apion Jiavipes; peas in the pod by 
the small beetle (Bruchus granarius). The wire worm is the 
grub of the beetle (Elater Segetis). The turnip-fly is properly 
a beetle, a little jumping beetle (Haltica nemo rum). 
The problem, of course, is, how to destroy this legion of ene- 
