On Irrigation in Tasmania . 
89 
water in small shallow saucers placed upon beds of 
perfectly dry straw and brushwood. The first two 
circumstances above enumerated cannot be prevented by 
man, but this third can; and, 'while in the Island, I have 
heard from various persons (who were merely stating 
facts without attempting to construct a theory) such 
statements as seem to admit of no other conclusion than 
that the presence of moisture is completely effectual in 
preventing the crops from being affected by frost—that 
is, in the low country. In the central table land, prob¬ 
ably, the air itself is sometimes below the freezing point 
when the summer is pretty well advanced ; and whether 
moisture would counteract its effect, I have no data to 
judge by: but it is of much less importance than the 
question of the summer frosts in* the low country. One 
gentleman informed me that a piece of marsh land be¬ 
longing to him, which had been particularly subject to 
summer frosts, was irrigated, and since then it had never 
suffered from them; aud another gentleman stated that 
his marsh land only suffered when there had been much 
drought before the beginning of summer : but that if the 
land was saturated with water late in the spring, it never 
was liable to be injured by frosts. 
On the fourth effect mentioned, viz. the destruction of 
the grub and caterpillar, it will be sufficiently obvious 
that a complete soaking of the land must effectually 
destroy these most destructive insects. It is well known 
that English grass is generally destroyed by the grub in 
the third year ; so that ordinarily it is impossible to keep 
land longer than that in pasture, and the importance of 
a remedy for so great an evil is easily perceived. The 
caterpillar also frequently destroys whole fields in a day 
or two : last year it did a great deal of damage to the 
westward of Westbury. Some rich land, in which every 
thing green had been entirely destroyed by the caterpillar 
