Fig. 4. represents the trough apparatus invented by Mr Cruickshanks; the plates of zinc and copper arc soldered together, and are then cemented into a wooden frame, leaving intervals between the double plates, to receive the fluid which is intended to act upon the zinc. It is pi ovided with wires at each cud, which are in opposite states of electricity, and may be applied to any substance which it is proposed to subject to its influence.
Fig. 5. represents the battery of Mr Children, which is a combination of the couronne des tasses of Volta and the trough of Cruickshanks. The plates are not in contact, but each pair is connected by slips of metal, and the whole is attached to a beam, so as to be lifted out of the cells at pleasure. The trough and partitions may be formed of either wood or earthen ware, and contain the fluid that is to act on the zinc plates.
Fig. 6. is the apparatus for receiving in separate ves sels the gases which arc evolved by the action of galvan ism upon water. The two small jars have metallic wires inserted at their upper end, one of which is connected with the positive, and the other with the negative extremity of the pile. They are filled with water, and inverted in the same fluid ; and the ends of the wires are so situated, that the gas disengaged from them rises to the top of the jar.
Fig. 7. represents the apparatus in which the gases dis engaged from water may be reconverted into water by the electric spark.
Fig. 8. are the agate cups, connected by amianthus, em ployed by Sir H. Davy in the decomposition of water ; and Fig. 9. are Abe gold cones employed in the same set of ex periments.
Fig. 10. represents the apparatus which Sir II. Davy employed for the decomposition of salts, and the transfer of their constituents. In Fig. I I. we have the combination of three vessels, in which the transfer is exhibited in a more striking manner.
Fig. 12. represents the apparatus for taking the galva nic spark in gases : it consists of a graduated glass tube, into which two wires are introduced, the one which en ters at the side being moveable, and capable of being ap proached to the- other; according to circumstances, they may be tipped with pieces of charcoal, or the wire may be bare.
Fig. 13. is a variation in the form, which may be em ployed over mercury. These instruments were invented by Sir H. Davy.
Figs. 15, 16, 17, 18. The dissected pile employed by De Luc, to illustrate the mode of its action. The shaded part
represents the moistened cloths, and the letters C and Z the copper and zinc plates respectively. In Fig. 15. the pile is continuous, in its usual form; Fig. 16 is the first dissection, Fig. 17. the second, and Fig. 18. the third. 'Fig. 14. is one of the wire stands that are interposed be tween the plates.
Fig. 19. represents the apparatus of M. De Luc : it con sists of two piles connected by a metallic rod at the bottom; between the upper ends is interposed the interrupted wires terminating in water, and to each extremity one of Bennet's electrometers is applied.
Fig. 20. represents the lower limbs of a frog, lying on a plate of metal, while another kind of metal is placed in contact with the spinal marrow ; these two metals arc then connected by a conducting body, and the muscles of the legs are thrown into convulsions.
Fig. 21. is Dr. Bostock's numerical illustration of the effect of the pile; the letters point out the nature of the substances, and the figures indicate the increase of power which the electricity acquires by passing along the instru ment. See Thomson's Annals, iii. 86.
Fig. 22. is an experiment of Mr Singer's, which is sup posed to disprove the hypothesis of electric energies. In this apparatus, each wire will have its ends in the oppo site states of electricity, one positive and the other nega tive.
Besides the references that we have made in the course of the article, the following works and papers deserve to be noticed, either as presenting an interesting view of the gradual progress of the science, or as containing an abstract of the hypotheses that have prevailed at different times.
Pfaff's Dissertation on Animal Electricity, 1793. Monro On Animal Electricity, 1793.
Cavallo On Electricity, vol. iii. 1795.
Halle's report to the French Institute, Journ. Phys. t. 47. 1798.
Cuvier's report, foam. Phys. 52. 1301.
Hachette's report, Journ. Polytechnique, 4. 1801. Report to the French Institute, Ann. de Chinz. 41. 1802. Reports made by Delamatherie in several volumes of his Journ. 41, 46, 48, 50.
Sue's History of Galvanism, 1803.
Cuthbertson's Practical Electricity, 1807.
Carpue's Introduction to Electricity and Galvanism, 1307.
Conversations on Chemistry, 5th conversation.
Some good remarks on galvanism occur in Thomson's History of the Royal Society, in NIurray's System, and in his Elements of chemistry. (x)