102 
the night when the action of the machine was suspended, but 
resumed its vigour, and again stood erect under its renewed 
action. These particulars, on the general correctness of which 
I have every reason to rely, are admirably illustrative of the 
principle, that a relative state of negation in the source of vege- 
tation from beneath, as compared with the positive state of the 
atmosphere, though without any absolute addition to the quan- 
tity of electric matter, is a most material requisite to its origin 
and progress. The general high temperature of the room no 
doubt aided considerably in the process. I lately observed, 
that whereas sprigs of plants inserted in water, from which the 
carbonic acid has been expelled by boiling, appear to perish 
nearly as rapidly as if they had been destitute of moisture: when 
the water is impregnated with an additional quantity of this 
gas they retain their vigour. It appears, therefore, highly pro- 
bable that this gas is essential, or greatly conducive, to the rise 
of the sap, in consequence of the affinity of its oxygen with the 
positive electricity of the atmosphere, while its carbon is sepa- 
rated from it and deposited in the leaf, or conveyed into tlie 
substance of the plant. The electricity of the air, as distin- 
guished from that of vapours and of solar light, has chiefly 
occupied the above remarks. My endeavour has been to show 
that the solar fluid is economised in it, to the exclusion, in a 
great degree, of the action of vapours and of the direct rays of 
light upon the shooting and expanding leaf, for the purpose of 
imparting the first excitement to the germ. The process of 
nutrition, in connection with an increased supply of electric 
matter, as the principle of vitality now becomes indispensable, 
and is accordingly administered in abundance. 
133 Flies to exclude from Houses. It seems to have been 
known to the ancients that the common House Fly (Musca 
domestica) may be deterred from entering apartments simply 
by extending a network of white thread before the openings of 
the room. The Italians sometimes adopt this plan, and for 
fruit houses, or even for wall trees, it may probably be of essen- 
tial sendee. It is further stated in the Transactions of the 
Entomological Society, I, p. 4, that “ if small nails be fixed all 
round the window frame, at the distance of about an inch from 
each other, and threads be then stretched across both vertically 
and horizontally, the apparatus will be equally effectual in ex- 
