1820.] Scientific Intelligence.. 467 



tion of granite, while at the same time the contemporaneous 

 existence of nodules of mica slate and granite in the granitic 

 envelope forms an additional proof to the many others that 

 •granite is not entitled to take precedence in all formations. 



IV. Insular Climate. By the Same. 



I found a fine corroboration of the opinion I gave on insular 

 climate, and which you were so good as to insert in your last 

 ■September number, in the state of the thermometers kept at the 

 Sell Rock, and in the signal station communicatino^ with it at 

 Arbroath. In the former, the range is uniform ; and in the lat- 

 ter, the changes are abrupt and irregular. 



V. Galvanism. By the Same. 



Any facts that can be communicated on the production and 

 operation of this singular and powerful agent seem deser.ing of 

 record, and you will, I dare say, forgive me for adverting to 

 some phenomena which have presented themselves in the course 

 of my experiments, and these may not be altogether unaccept- 

 able to the practical electrician. I constantly use the galvanic 

 triads, for which we are indebted to the ingenuity of that enlight- 

 ened and distinguished philosopher Dr. WoUaston, and a com- 

 parison between this arrangement and the common form of the 

 trough is altogether out of the question, at least in its powers of 

 igniting platinum, and deflagrating the metals, 8cc. 



I use only three instruments in my experiments, each contain- 

 ing 10 porcelain cells, the triads being four inches square. 

 About 4 lbs. of nitrous acid are expended, and I add merely 

 double the quantity of water, which occupies about one-third of 

 the cells, and seems to act much better than when the cells are 

 full to the top. This always affords me a series of most imposing 

 phenomena, and by this arrangement I can ignite 8 to 10 inches 

 of platinum wire of 100th inch diameter to whiteness. When I 

 deflagrate gold, silver, &c. foils, I plunge the extremity of one of 

 the conducting rods into a flat glass dish containing mercury, 

 say a foot diameter, and brush the surface with the foil sus- 

 pended from the other arm. The deflagration is then of the 

 most brilliant description, because the sweep is extensive. 



It is material to have the conducting wires of considerable 

 diameters ; I never use them less than one-eighth of an inch. 



I have elsewhere pointed out the fact that when the plates are 

 heated in a sand-bath, or the acid medium into which the plates 

 are plunged, raised in temperature, there is a decided increase 

 of action, and that the energy is at least renewed by raising the 

 plates, and suspending them for a short period in the atmosphere. 



When nitric acid is used, the rinc alone is corroded, but in a 

 mixture of sulphuric and nitric acids, then both copper and 

 ■zinc are dissolved, and much acid vapour is developed, exceed- 

 ingly annoying to the operator. 



2g 2 



