THE EARTH’S INTERNAL HEAT.
To the Editor. Sir, —In the short article of Oct. 18, on the earth’s internal heat, as suggested by the thermometer’s registration of the temperature in the shaft of the Magdala Quartz Company, Victoria, the statement is made that “ Science will have to considerably modify her interpretation of the great heat at the bottom of many European mines of no greater depth. ” If none else have done so I would ask you to find room foe a few lines expressive of doubt as to the correctness of the above statement.
In the first place, it may be presumed that the thermometer used in the Magdala shaft was a very good one of the ordinary kind, but it is doubtful, I think, whether the measurements were made by the aid of one of those exceedingly delicate selfregistering instruments which are used by men of science to obtain measurements of the most perfect accuracy. Secondly, the measurements were not taken by experts for the purpose of scientific investigation, and it may therefore be supposed that there was not observed that perfect precision and exact attention to minutiae which characterises the experiments and observations of scientific men.
Thirdly, when measurements are made for the purpose of determining the heat of the interior of the earth it is not (as appears to be the case in the Magdala mine) the atmospheric temperatuie which is measured ; but the temperature of the rocks. Now, the registration given in the article referred to is that of the temperature of the mine office, and with the thermometer suspended 17ft. from the bottom, compared with that in the office on the surface of the ground. Fourthly, in ascertaining the temperature of the rocks, those only which are uniform in substance and form are considered to give data of importance as it is found that the nature of the rock, the dip of the strata, the quantity of contained water and other circumstances will considerably modify the temperature of the rocks in the same locality.
Fifthly, in the article referred to, the temperature at the bottom of the Magdala shaft (83 deg.) is compared with the temperature in the office on the surface of the ground (80 deg.) This, 1 think, shows that the investigation was not carried on by experts, as 1 just now hinted, because it is known that the earth is affected appreciably by the heat of summer and the cold of winter to a depth of 100 ft from the surface, at which depth the temperature is about that of the mean annual temperature of the locality, and it is only the registration of the thermometer below this limit which should be compared, as it is evident that the registration in the office would vary with the seasons ; so that science will not have to considerably modify her views, notwithstanding the manager of Magdala mine. When I began I intended to refer to the terms molten and vaporised as applied to the interior of the earth in the article referred to, with a view to show that the earth is not molten, as used to be supposed, but rigid to the centre ; but I am afraid that I have now made the letter too long. If you find a corner for this, I may trouble you again. The article, which is somewhat misleading, got into your valuable columns, no doubt, inadvertently, and I thought you would be glad to have it corrected. I am, &c., B. J. Wbstbkooke.
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