358 



GALVANISM GAMA. 



yegativt Eltctrla. 

 Huron. 

 Carbon. 

 Antimony. 

 Tellurium. 

 Colunibium. 

 Titanium. 

 Silicon. 

 OMIIIIJIU. 



H ydrogen. 



Positive Electrics. 

 Zinc. 

 Cadmium. 

 Iron. 

 Nickel. 

 Cobalt. 

 Cerium. 

 Lead. 

 Tin. 



BUrautb. 

 Uranium. 

 Copper. 

 Silver. 

 Mercury- 

 Palladium. 

 Platina. 

 Rhodium. 

 I rid mm. 

 Gold. 



Before concluding this part of the subject, it should 

 he remarked, that in the production of the different 

 effects arising from the operation of galvanism, a 

 different law is observed with regard to each of these 

 effects, according as the structure of the galvanic 

 arrangement varies. Thus, a few metallic plates, of a 

 surface with two or three square feet, will be power- 

 ful in producing heat and light, and will therefore 

 deflagrate metallic leaves placed in the circuit, and 

 illuminate charcoal points vividly ; but the battery 

 which they form will display little power of electrical 

 attraction and repulsion, will have comparatively 

 little effect on sentient organs, scarcely producing any 

 shock, and will act feebly in producing chemical de- 

 composition. Thus the great battery of Mr Children 

 and the deflagrator of Dr Hare, which melted many 

 feet of platina with ease, liad no very remarkable 

 power in effecting decomposition, or in giving shocks. 

 If the same amount of surface, however, as existed in 

 either of these arrangements, had been disposed in a 

 battery, so as to have formed four times the number 

 of plates, the result would have been that the burning 

 effect would have been diminished,while it would have 

 exhibited more evidently different electrical states, 

 and been more powerful hi exciting sensations in ani- 

 mal organs and effecting chemical decompositions. 



4. Theory of Galvanism. The various attempts 

 which have at different times been made to explain 

 the phenomena of galvanism, by the application of 

 the laws which are known to govern those of ordi- 

 nary electricity, have, on the whole, been attended 

 with little success ; and the theory of this branch of 

 philosophy still remains involved in considerable un- 

 certainty. We do not yet understand the nature of 

 that force which originally disturbs the electrical con- 

 dition of the different parts of the voltaic apparatus, 

 and constitutes the primary source of galvanic power. 

 Volta conceived that it proceeds solely from the con- 

 tact of the metals, the interposed solutions operat- 

 ing merely as conductors, by means of which the 

 electricity developed by each pair of plates is con- 

 veyed from one part of the apparatus to the other. 

 But in proportion as a more extensive acquaintance 

 with the phenomena afforded the means of a more ac- 

 curate analysis, the insufficiency of this, which was 

 termed the electrical theory, became more apparent ; 

 and it is now regarded as fully established, that the 

 primary agent in the evolution of electricity, is the 

 force of chemical attraction. This latter view of the 

 subject has led to what may be called the chemical 

 theory of galvanism. The basis of this theory de- 

 pends upon the following facts, namely : That no 

 sensible effects are produced by a combination Jorm- 

 ed of substances which have no chemical action on 

 each other ; that the action of the pile is always ac- 

 companied by the oxidation of the zinc, and that the 

 energy of the pile in producing chemical decomposi- 

 tions and other galvanic effects is in some proportion 

 to the activity of the chemical action within the ap- 

 K>aratus itself To this theory it may be objected that 



the mere contact of substances, without any chemical 

 change whatever, is adequate to the excitement of 

 electricity ; and that galvanism, to an extent capable 

 of decomposing water, may be excited by a galvanic 

 combination in which no chemical action whatever 

 occurs. The third theory, and which was proposed 

 by Sir H. Davy, is intermediate between the two 

 others. It, in some measure, removes the difficulties 

 peculiar to each, by attributing the galvanic excita- 

 tion to the combined influence of the electro-motive 

 powers of the metals, and the chemical action of the 

 liquid. The commencement of the process, it is con- 

 ceived, is that the zinc and copper plates, by their 

 contact, break the electric equilibrium, in the manner 

 supposed by Volta, and, in consequence, the one metal 

 becomes positive and the other negative. All the 

 zinc plates in the series thus become, at the same 

 moment, positively electrified, and all the copper 

 ones negative ; and by means of the conducting fluid 

 with which the cells are filled, the electricity accumu- 

 lates on one side of the battery, and the other becomes 

 as strongly negative. But the quantity of electricity 

 thus excited would be insufficient, as is maintained, 

 for causing energetic action. For this effect the 

 electric equilibrium of each pair of plates must be 

 restored as soon as it is disturbed, in order that they 

 may be enabled to furnish an additional supply of 

 electricity. The chemical substances of the solution 

 are supposed to effect that object in the following 

 manner : The negative ingredients of the liquid, 

 such as oxygen and the acids, pass over to the zinc ; 

 while the hydrogen and the alkalies, which are posi- 

 tive, go to the copper ; in consequence of which both 

 the metals are tor the moment restored to their natu- 

 ral condition. But as the contact between them 

 continues, the equilibrium is no sooner restored, tha 

 it is again disturbed ; and when, by a continuance of 

 the chemical changes, the zinc and copper recover 

 their natural state, electricity is again developed by 

 a continuance of the same condition by which it was 

 excited in the first place. In this way the theory 

 explains why chemical action, though not essential to 

 the first development of electricity, is nevertheless 

 necessary for enabling the voltaic apparatus to act 

 with energy. This theory may be regarded as more 

 probable than either of the former. The chief diffi- 

 culty which is attached to it, is in explaining how the 

 elements come to be evolved in opposite electrical 

 states ; for it has already been remarked, that the 

 opinion that all bodies are naturally, whether com- 

 bined or insulated, in peculiar electric states, is a 

 mere assumption. For the effects of galvanism, on 

 the magnet, see Electro- Magnetism. 



We nave thus concluded our view of what may 

 be regarded as the present state of this important 

 branch of science ; but from the results which have 

 been obtained by recent experiments, it is reasonable 

 to infer that our knowledge on this subject will, ere 

 long, be greatly enlarged. The late researches of 

 Mr Faraday, as well as some of the continental phi- 

 losophers, justify such expectations, and in order to 

 furnish our readers with an account of the most 

 recent discoveries in galvanism, the subject will be 

 again resumed in our article Foltaic Electricity. 



GAMA, VASCO DE, born at Sines, a small seaport 

 of Portugal, of a noble family, discovered the route 

 to the East Indies by sea a discovery of the greatest 

 importance, not only in regard to commerce, but to 

 the civilization and political relations of Europe, and 

 which laid the foundation of the commercial power 

 of Portugal in the Indian seas. As soon as the 

 pupil of Henry the Navigator, Emanuel the Fortun- 

 ate, had ascended the throne, he determined to 

 carry into execution the project of sailing to India 

 round the cape of Good Hope (discovered in 1480. 





