146 G. P. Scrope — On the Internal Fluidity of the Earth. 



globe, seem to be very vague as to tbe meaning they attacb to the 

 word ' fluidity.' Some, like Mr. Hopkins, have used the phrase in 

 its strict mathematical sense, excluding all consideration of internal 

 friction — a sense utterly inconsistent with any conceivable condition 

 effused rock. Others seem to have had in tlieir minds a degree of 

 fluidity which would allow the matter always to find its own level, 

 and yield to pressure by moving in the direction of least resistance 

 with the facility of water in a siphon. A reviewer of Professor 

 Phillips's work in the PaU Mall Gazette of March 10th, even asserts 

 unhesitatingly that Palmieri's novel and recent observations on the 

 seemingly tidal influence of the sun and moon upon the activity of a 

 volcano in eruption, prove that " the lava ocean under Vesuvius 

 must be enormous and comparable in size to the Atlantic or Pacific," 

 because " tidal influence only produces appreciable effect on the 

 largest sheets of water." Surely there is no need of such an as- 

 sumption. If Professor Palmieri's idea of the tidal influence of the 

 attraction of the sun and moon on volcanic activity — in itself extremely 

 probable — be shown by further observations to be correct, it will only 

 amount to a corroboration of that which many years since I put for- 

 ward (and which Sir C. Lyell has adopted) as to the similar influence 

 of varying barometric pressure on the action of Stromboli and other 

 volcanos, whose lava ducts are at the time in open communication 

 with the atmosphere. The elasticity of the steam and other gases 

 contained within or beneath the lava, seizes the opportunity for ex- 

 pansion afforded by diminished atmospheric weight in this case, just 

 as the tidal wave rises through the lateral pressure of the sur- 

 rounding oceanic waters, when its own gravity is reduced by the 

 moon's attraction. In the case of the volcano, there is evidently no 

 need to imagine any lateral movement of highly liquid lava towards 

 the vent, to account for slightly increased flows of lava, or steam 

 explosions at the tidal periods. Nothing, therefore, in M. Palmieri's 

 observations tends to support the hypothesis of the existence of vast 

 oceans, still less of a continuous belt, of fluid matter, beneath the 

 earth's crust — in itself, as I have shown, an improbable supposition. 

 Many facts tend to show that " lava," the only fused rocky matter 

 in nature with which we are acquainted, is, when it issues from the 

 interior of the earth during volcanic eruptions, extremely viscous ; 

 and though some currents are seen to flow down an incline so low 

 as &° or 8° with a velocity of three or four miles an hour, others are 

 so sluggish as to accumulate in bulky masses beside or over the 

 orifice whence they are expelled. If it be suggested that in the 

 depths of the volcano the fluidity of the lava is probably very 

 much greater, owing to its higher temperature, this idea is, I think, 

 inconsistent with many well-known facts, such, for example, as the 

 occasional efflux of liquid lava from the summit of Mauna Loa in 

 Hawaii, while that in the crater of Kilauea at a level of 10,000 feet 

 lower, and only 16 miles distant, remains unaffected. So, also, M. 

 Deville saw on the summit of Vesuvius, in 1856, two closely adjoin- 

 ing minor craters, in one of which a pool of incandescent lava 

 bubbled up, while the bottom of the other, at a lower level by 300 



