208 The Central Mass of the Globe in a state of Igneous Fusion. 



On reading these passages, it certainly appeared to me that the pertur- 

 bations thus indicated, as probable consequences involved in the hypothesis 

 in question, were very materially exaggerated, especially in Mr. Lyell's 

 view, and were in a great degree inconsistent with the very conditions 

 which that hypothesis necessarily assumes. 



I by no means wish to pledge myself to a dogged defence of this par- 

 ticular hypothesis ; but still it is surely quite as unphilosophical to argue 

 against an hypothesis without giving it the advantage of a fair examination 

 of its own essential conditions, as it is to maintain such an hypothesis as 

 firmly established, while our evidence must probably always remain so very 

 imperfect and inadequate. I shall shortly therefore invite the attention of 

 your readers to the general conditions of the hypothesis in question, and 

 the conclusions which appear to be logically deducible from these conditions. 

 The temperature of the earth has been ascertained from very numerous 

 and independent observations in deep pits in different countries, to increase 

 as we descend at the rate of about 1° Fahrenheit for every fifty feet, or 

 about 100° Fahrenheit per mile. Now if we suppose that the increase pro- 

 ceeds in any thing like the direct proportion of the depth, rocks of the 

 constitution of basalt, (which melts at forty Wedgwood)* would become 

 fluid at about thirty-three miles, and the more refractory metals, such as 

 iron, nickel, and platina, at about one hundred and fourteen miles of 

 depth. 



Now, on these suppositions, it should seem to follow as the fundamental 

 condition of this hypothesis, that it would represent the crust of the earth 

 as quite solid to the depth of between twenty and thirty miles ; beneath 

 which we cannot conceive that the interior mass would at once become 

 perfectly fluid ; the more probable conclusion must be (on the grounds of 

 the hypothesis) that the first or highest portions would be only rendered 

 to a slight degree viscid, and this viscidity would increase for nearly ninety 

 miles more, before, from the fusion of the more refractory materials, any 

 thing like a perfectly fluid mass would result. Now I need not dwell on 

 the great resistance which such a consistency would oppose to any violent 

 tidal waves, nor how fatal it seems to Mr. Lyell's notion oijets of lava ^ the 

 utmost effect indeed which could be produced in the volcanic vents by the 

 ebb and How of such subterranean tides would be a tranquil elevation of 

 a few feet, unless their effect were aggravated by a configuration of the 

 interior, which seems inconsistent with the views concerning its structure, 

 naturally suggested by the hypothesis. On communicating these views to 

 a scientific friend, far more competent than myself to arrive at just conclu- 

 sions on a subject involving dynamical principles, I received the following 



* I here follow Morreau's Comparative Tabic of the Degrees of Wedgwood's 

 Pyrometer, as related to Fahrenheit's Thermometer. 



