182 report— 1878. 



slow upward flow which supplies the water for this gradual discharge 13 

 favourable to the accuracy of the observations (which have always been 

 taken at the bottom,) by checking the tendency of the colder and 

 heavier upper water to descend and mix with the lower. As bearing on 

 the subject of the disturbance of temperature by the stirring of the 

 water in boring, as well as by the generation of heat in the concussions of 

 the tool, it may be mentioned that the last observation before the month's 

 interruption by the jamming of the tool was o7°'5, at 886 feet, and the 

 first observation after the extraction of the tool, was 57 o- 0, at 898-6 feet ; 

 the former being on May 20th, and the latter on July 1st. The smallness 

 of the difference between these two temperatures seems to indicate 

 smallness of disturbance by the action of the tool. 



It appears from these various circumstances that the observations are 

 entitled to considerable weight, and that the rate of increase of tempera- 

 ture downwards at Liverpool is exceptionally slow. It will be remembered 

 that the rate found by Mr. Fairbairn, at Dukinfield Colliery, in the 

 adjacent county (Cheshire), was also very slow, though not nearly so slow 

 as that indicated by these Liverpool observations. — (See our Report in 

 the Volume for 1870.) 



Mr. E. Wethered, of Weston, near Bath, has also commenced obser- 

 vations in a colliery in that neighbourhood. Mr. J. Merivale, of Ned- 

 derton, near Morpeth, has received a thermometer for observations in a 

 colliery. Mr. J. T. Boot, of Hucknall, near Mansfield, has received a 

 second thermometer (in place of a broken one) for observations in a deep 

 bore, and Mr. Rowland Gascoigne, of the same town, has received one for 

 a similar purpose. 



In the eleven years which have elapsed since the appointment of this 

 Committee, a large amount of useful work has been done, by methods of 

 observation not requiring any elaborate or expensive appliances, or any 

 special training on the part of the observers. 



Two difficulties are encountered in investigating underground tem- 

 perature. We have to contrive instruments which shall truly indicate 

 the temperature at the point of observation, and we* have further to 

 ensure that this temperature shall be the same at the time of observation 

 as it was before the locality was artificially disturbed. 



As regards the first of these difficulties, the Committee have been 

 completely successful, and have largely increased the resources at the 

 command of observers. 



But in regard to the second difficulty, the same amount of success 

 has not been attained. The circulation of water in bore-holes and of air 

 in mines are disturbing elements difficult to deal with. Even such firm 

 plugging as was employed to isolate portions of the water-column in the 

 great bore at Sperenberg cannot altogether remove the error arising from 

 convective disturbance ; for the long-continued presence of water at a 

 temperature different from that proper to the depth affects the tempera- 

 ture of the surrounding rocks, and the temporary isolation of a short 

 column would not abolish this source of error, even if the plugs them- 

 selves were impervious to conduction and convection. 



After the experience which has now been gained of rough and ready 

 methods, it is time to consider the propriety of resorting to a more- 

 special method, which has been more than once suggested, but has 

 hitherto been postponed on account of the additional labour and skill 

 which would be requisite for carrying it out. 



