ON tJNDERGROTTND TEMPERATURE. 35 



•which is all the more remarkable because the pressure (which tends to make 

 the reading higher) must have increased with the depth. At the bottom, or 

 rather at 3837 feet, being 6i feet from the bottom, the temperature indicated 

 was 105°. Either of these results, taken apart from the other and compared 

 with the surface-temperature, would give a result not improbable in itself. 

 The mean temperature of the air at St. Louis appears to be about 53°. But 

 it seems desirable to avoid publishing calculations till the data are better 

 established. 



Unfortunately the apparatus which was emploj-ed in boring has all been 

 removed, after the insertion of two wooden plugs, with an iron screw at the 

 upper end of each, one at the offset at a depth of 1022 feet, and the other at 

 the offset at the depth of 953 feet, for the purpose of separating the fresh 

 from the salt waters. These plugs were driven in with great force, and can 

 onlj' be withdrawn with the aid of a series of poles and other appliances, 

 such as were used in the boring, w^hich will be rather costly. The poles alono 

 are estimated to cost ^1152, or about ^200. If the plugs were withdrawn 

 (and according to Dr. Stevens there is nothing but the expense to prevent 

 it), the whole well would be available for observation. The Committee will 

 make every effort to prevent so rare an opportunity from being lost. 



The Secretary has also been in correspondence with Messrs. Mather and 

 Piatt of Salford Iron-works, respecting a boring at Moscow, for which they 

 have furnished machinery, and which is to be carried to the depth of 3000 

 feet. They refer to General Helmersen, of the Mining College, St. Peters- 

 burg, as the best authority to whom application can be made for particulars of 

 the Moscow boring as to temperature &e. The Secretary has accordingly 

 written to General Helmersen, endeavouring to interest him in the objects 

 of the Committee, and offering to forward thermometers. No reply has yet 

 been received. 



An element which it is necessary to know with a view to the correct re- 

 duction of our obseiTations, but which in many instances it is difficult to 

 obtain by direct observation, is the mean annual temperature of the ground 

 at or near the surface. Instances frequently occur in which the temperature 

 at the depth of 200, 300, or it may be 500 feet is accurately known, while 

 the temperature in the superincumbent strata can only be guessed at. This 

 is the case at the Kentish-Town Well, and partially at Eose Bridge and 

 Dukenfield Collieries. 



It is very desirable that, in connexion with temperatures at great depths, 

 there should in each locality be an accurate observation at a depth of from 

 50 to 100 feet. At such depths in the solid groimd, before it has been dis- 

 turbed by mining-operations, one observation suffices to give a good approxi- 

 mation to the mean temperature of many years. At depths of 2 or 3 feet it is 

 necessary to observe once a week or so throughout a year in order to get the 

 mean temperature at that depth for that year ; and this may differ by a con- 

 siderable amount from the mean of a series of years. 



In the Eeport of the Scottish Meteorological Society for the quarter end- 

 ing December 1862, there is a comparison of the mean temperature of the 

 air with that of the soil at the depths of 3, 12, and 22 inches at four stations, 

 from observations extending over five years ; and in the Journal of the same 

 Society for the quai-ter ending December 1865, there is a comparison of the 

 temperature of drained and undrained land from one year's observations un- 

 dertaken for this purpose at two stations, and including also a comparison 

 with the temperature of the air. The mean temperature of the air for each 

 day is in these comparisons assumed to be the simple arithmetical mean of 



d2 



