176 REPORT— 1869. 



thermal conductivities of two metals are as the squares of the foreshorienings 

 in their respective curves of statical temperature. I have not considered my 

 observations sufficiently exact (chiefly on account of the imperfection of the 

 thermometers) to warrant my undertaking the labour of calculating the con- 

 stants of empirical formulae to represent them, but have contented myself 

 with results derived from tracing, libera manu, curves closely representing 

 the result of experiment. 



I may mention, in concluding this provisional Report, that an air-bath has 

 been found preferable to melted solder for heating the bars employed in the 

 cooling experiments, and that the conductivity of copper is so much superior 

 to that of iron that, when a source of heat above 100° C. is employed, the 

 further ends of the 8-feet copper bars require to be kept cold by a constant 

 stream of water. In this case the curve of statical temperature undergoes 

 an ob^aous and easiLv allowed for modification. 



Report of the Committee for the purpose of investigating the rate of 

 Increase of Underground Temperature downwards in various Loca- 

 lities, of Dry Land and under Water. Draivn up by Professor 

 Everett, at the request of the Committee, consisting of Sir "William 

 Thomson, XL.Z>.,F.2?.<S., E.W.Binney, F.R.S.,F.G.S., Archibald 

 Geikie, F.R.S., F.G.S., James Glaisher, F.R.S., Rev. Dr. 

 Graham, Prof. Fleeming Jenkin, F.R.S., Sir Charles Lyell, 

 Bart., LL.D., F.R.S., J. Clerk Maxwell^ F.R.S., George Maw, 

 F.L.S., F.G.S., Prof. Phillips, LL.D., F.R.S., William Pengelly, 

 FR.S., F.G.S., Prof. Ramsay, F.R.S., F.G.S., Balfour Stewart, 

 LL.D., F.R.S., G. J. Symons, Prof. James Thomson, C.E., Prof. 

 Young, M.D., F.R.S.E., and Professor Everett, D.C.L., F.R.S.E., 

 Secretary. 



In the last Eeport it was stated that several small hardy maximum ther- 

 mometers suited for rough work were being constructed by Casella under the 

 direction of the Committee. These instruments have now been in use for a 

 year and have been found to work well. 



Their construction is as follows: — APhiUips's maximum thermometer, about 

 10 inches long, graduated in Fahr. degrees from about 30° to 90°, is her- 

 metically sealed within a glass tube, which is about three-quarters filled with 

 air and one-fourth with alcohol, the thermometer being kept from touching 

 the tube by cork rings. The thermometer thus enclosed is inserted in a 

 copper case for protection, contact between the glass and the copper being 

 prevented by india-rubber. The air within the hermetically sealed tube 

 prevents the great pi-essure which acts upon the exterior of the tube in deep 

 bores fiUed with water from being transmitted to the thermometer within. 

 The use of the alcohol is to lessen the time required for the thermometer to 

 come to the temperature of the surrounding medium. 



The Committee would take this opportunity of stating that they will be 

 happy to supply these instruments to any persons who wiU undertake to make 

 observations of the tempei'ature in borings. 



Mr. M'Farlauc (assistant to iSir AV. Thomson), who furnished for the last Ee- 



