Penny Blood: Serial Sensation and Working-Class Entertainment — page 31: what you’re looking at

Machine-transcribed from the original scan — historical spelling and the odd misread are preserved.

14 ON UNDERGROUND TEMPERATURE. (CH. I. enclosed in a cylindrical hole within a mass of rock, the rock extending to an infinite distance both sideways and downwards. The water in the bore-hole at any given depth has, in con- sequence of the currents, a temperature which differs from that of the rock on the same horizon at a distance from the hole. This temperature of the water may be higher or lower than that of the rock; but we will suppose it lower, as it will be in the deeper parts of the hole. The rock surface of the bore-hole, being constantly laved by the water, has been brought to the same temperature as the water. It necessarily follows from this that if we could examine the temperatures of the rock at greater and greater distances laterally from the bore-hole, we should find them become higher and higher, and we should have to penetrate to some considerable distance before the increase came to an.end, and when it did so we should feel assured that at last we had reached rock of the true temperature for the depth. The greater might be the difference between the temperatures of the water and the rock in mass, the further we should have to penetrate for that purpose, and this would be furthest in the lower portions. Now suppose the currents interrupted by lowering the geo-thermometer, so that the heat _ ceases to be conveyed away from the rock surface of the bore- hole ; and we will now dismiss the consideration of the effect of the water above and below the disks of the instrument. The heat which flows out of the sides of the bore-hole into the imprisoned water is now no longer conveyed away by the currents, and begins to accumulate there. The rock in the neighbourhood of this water begins to get warmer. The region of the true rock temperature approaches nearer and nearer to the bore-hole, until at last it reaches it, and then, and not until then, the imprisoned water assumes the true temperature of the rock. ‘This process will require time, and that a long time. In the first place, on account of the great capacity of water for heat, it requires much more heat to warm up a volume of water through a given range of temperature than it would require to warm up an equal volume of rock. In the second place, it requires a-long time for the heat to travel through the rock to reach the water. And although the conductivity of rock salt is said to be considerably higher than that of COMIC OOOKS.EO