from Snails and Slugs. 225 



that that most destructive insect, the Forficula auricularia LinncBus, could 

 not pass from under the barrier (c d) without using its wings. I apprehend 

 they could not hold by their feet to the zinc in its position c d, but would 

 fall to the ground in attempting to pass from d to c. 



The practice of placing small flower-pots, filled with dry leaves, in an in- 

 verted position over the tops of plant-rods is well known, and adopted for 

 capturing these insects. The zinc strap is admirably adapted to bring the 

 same system into practice for the protection of wall trees, thus : suppose, along 

 the edge of the zinc strap next the wall, holes to be made, about an inch in 

 diameter, one, two, or more yards from each other, and these closed bv loose 

 covers, of a shape capable of being easily removed, and of holding dry leaves ; 

 the gardener, by walking round his walls once a day, would be enabled to 

 secure great numbers of this destructive tribe, particularly during the season 

 before they take wing. This arrangement, T believe, would operate thus : an 

 insect creeping up a wall or stem of a fruit tree meets with obstruction at d, 

 and, being prevented from proceeding in that direction, instinctively runs hori- 

 zontally along the angle, in search of an outlet, when it very soon enters one 

 of the openings with its cover full of leaves, the kind of shelter in which it 

 delights ; others follow, until the spaces between the leaves are full. I think 

 this is not too much to expect, for in either direction the angle forms a channel 

 to conduct the current of insects into the very reservoirs where the gardener 

 wishes to find them. I am not certain that the galvanic arrangement operates 

 on these dry animals, but on the moist tribe MoUusca it does powerfully. I 

 must now take leave of the subject, and beg to subscribe myself. 



Sir, respectfully, your obedient Servant, 



Wm. Walker. 



Arthur Aikin, Esq., the Secretary at the Society 

 of Arts, Adelphi, London." 



Sometime before receiving the above communication we had 

 prepared the following paragraph from two articles which ap- 

 peared in the Gardener's Chronicle. 



The sensation of galvanism is produced by placing in contact 

 plates of zinc alternating with plates of copper, with a piece of 

 moistened cloth between each. This forms what chemists call 

 the galvanic battery; and it is by exciting this chemical power 

 in its simplest and feeblest form, that the efficacy of the galvanic 

 protector depends. If a snail or slug be placed on a plate of 

 zinc, to which a narrow plate or strip of copper is fixed near the 

 edge, and the zinc turned over it so as to form a rim of zinc, 

 copper, and zinc, it creeps unmolested on its surface ; but as 

 soon as it touches the rim where the copper is it receives a gal- 

 vanic shock (its moist soft body acting as the moistened cloth 

 above mentioned, and thus forming the galvanic circle complete), 

 and immediately recoils, twisting itself back, and rarely ven- 

 turing a second time to touch the copper, to receive another 

 shock. To protect a crop or plant, then, it is only necessary to 

 have a zinc plate of sufficient length to surround it, of 5 or 6 inches 

 in breadth, with a strip of sheet copper 1 in. broad riveted to the 

 upper part of the strip of zinc, and the zinc turned over it so as 

 to form a rim, as shown in Jig. 37. The plate so prepared is to 

 be set on edge round the bed or plant to be protected. The 

 cost of the plates complete is said to be about 6d. a lineal foot, 



Q 2 



