Penny Blood: Serial Sensation and Working-Class Entertainment — page 24: what you’re looking at

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

cu.1.] ON UNDERGROUND TEMPERATURE. 7 more than a degree Réaumur from the temperature of the water at the same depth, as shown by the first-named thermometer, when the water above and below was not cut off Now, it can hardly be supposed that so great a difference as this really ex- isted simultaneously between the surface of the rock exposed to the water in the bore-hole and the water itself. On the con- trary, it seems evident that the surface of the rock, being ex- posed to the action of the water, must have assumed the tem- perature of the water, whatever that might be, at any given depth. But the water was undoubtedly affected by convection currents, and consequently its temperature was not the same as that of the rock i mass at a distance from the bore-hole. Hence, when the circulation of these currents was stopped by the disks, the surface of the bore-hole would begin to tend towards the true rock temperature. If the water at any depth was warmer than the rock in mass, its temperature would begin to fall when the currents were cut off, and if the water was cooler than the rock it would begin to rise. Let us, then, shortly consider the general effect of con- vection currents as they would affect the water. These currents arise from the circumstance that when water is warmed it expands, and consequently becomes lighter. This expansion is exceedingly small ; yet in a substance of such ex- treme mobility as water it is sufficient to cause the expanded portions to rise, while the denser portions above sink to supply their place. The expanded portions in rising carry their heat up with them, and the cooler portions in sinking reduce the tem- perature of the lower part of the column. If therefore we hada column of water originally warmed towards its lower portion, but not supplied there with fresh accessions of heat, the whole would, if open to the atmosphere, shortly assume an equable temperature throughout. Let us now invoke the aid of a diagram to render our ideas more clear; and suppose the depths in the bore-hole to be measured along the vertical line OX, and let lines drawn at right angles to this represent, in proportion to their lengths, the temperatures at the corresponding depths. Let OA repre- sent the mean temperature of the surface of the ground. Then GONG oOo SS (CO)