On Chmical Fh'ihsophji 4*? I 



City in one instance and galvanism in another; and what con- 

 Btitutes the apparent difference between them ; — why, for in- 

 st.ince, galvanism exists in a lower state of intensity than elec- 

 tricity in producing shocks ; why it is less rapid in its move- 

 nientSj &:c.; — why again its pov.er of producing chemical effects is 

 so much greater than that of electricity*; why again the colorific 

 rays of the prism produce chemical effects, while the calorific 

 scarcely produce any ; why they are more refrangible than the 

 heat-making rays? — colour and light depending (as will, I 

 trust, be e\ ident when we come to the particular consideration 

 of light) on the partial solution of substances in this power, and 

 that light h tliepkcenomenon attending the ignition and sohUionf 

 or separation and condensation, of matter. So that heat and 

 light may be contrasted with each other, in the same xvay as we 

 have hinted above galvanism and electricity may be contrasted. 

 Hence, as in galvanism, the colorific or light-making rays are 

 those which, in consequence of holding something in solution, 

 are in proportion to this, and the unequal thickness or density 

 of substances, as drops of water, cut glass, knots of glass, a glass 

 prism, &:c. divided in their passage through them, meeting with 

 a greater or less degree of resistance, according to these va- 

 riations of thickness and their own variations of tenuity : and 

 besides this, their chemical relations to each other, or the mutual 

 affinities they exert on each other. It is thus these dfferences 

 of refrangibility, reflection, polarization, &c. are produced, and 

 not by differences in the size of the particles. 



It will from the same considerations also apftear very evident, 

 why I conceive th^t the heating and melting effects which the 

 disengagement of caloric from one body and its transference to 

 another, or that of mixing bodies of different degrees of tempe- 

 rature together, have not correctly ascertained or measured the 

 relative quantities of caloric, or of the quantity they contain or 

 retain in any state. That, consequently, the tables of capacity 

 are in some instances erroneous ; that the heating and melting 

 effects dejjend not merely on its quantity, but also on the time 

 it has to produce ''the effect, whether it is retained, or rapidly 

 escapes in its irresistible, attenuated, and unconfinable form. 



Thus having stated or anticipated in general terms the 

 more particular explanation of the various effects and phasno- 

 tnena which arc produced by one power, it will be necessary that 



♦ See the article Galvanlum, in the Edinburgh Encyclopaedia, where some 

 of the above questions arc stated, as questions which require to be an- 

 swered before we can fully understand the nature of either electricity 

 or galvanism. These questions will, I think, be satisfactorily answered 

 in the next Essay. 



I be 



