36 REPORT — 1870. 



the maximum and minimum, as indicated by self-registering thermometers 

 4 feet from the ground. From these observations it appears that the mean 

 annual temperature of the soil was in every case rather above that of the air, 

 and that the excess was greater for sand than for undrained clay, and was 

 greater for drained land than for the same land undrained. 



The greatest excess occurred in the case of the 22-inch thermometer at 

 Nookton (Vale of Leven), where both surface and suhsoU are sandy and dry. 

 The five-yearly means at this station were : — 



Air 46-1 ; soil at 3 inches 46-3, at 12 inches 47-3, at 22 inches 48-0, 

 giving an excess of 1-9 for the temperature at the depth of 22 inches as 

 compared with air. 



The smallest excess, in the case of the 22-inch thermometers observed for 

 five years, was at Linton (East Lothian), where it amounted to 0-7 ; but the 

 observations on the effect of drainage gave for the j'^ear of observation an 

 excess of only 0-2 at the depth of 30 inches in light sandy but undrained 

 soil, under a rye-grass crop, at Otter House, near Loch Fyne the corre- 

 sponding excess for drained land of the same kind and in the immediate 

 vicinity being 0-9. 



The mean temperature, at the depth of 3 feet, at Professor Forbes's three 

 stations at Edinburgh, from five years' observations, gave an excess of 0-5.5 

 above the mean temperature of the air at Edinburgh as determined by 

 Mr. Adie's observations. 



Observations on soil temperature in England are much needed ; but the 

 Greenwich observations give an excess of soil above air temperature falling 

 within the limits above quoted, the excess at 3 French feet being 1"7, while 

 at 24 French feet it is reduced to 1°. The soil of which the Observatory 

 Hill is composed, and in which the thermometers are sunk, is dry gravel, 

 and the unusual circumstance of decrease of temperature downward observed 

 in the comparison of the 3-feet and 24-feet thermometers, seems to indicate 

 that the surface of the hill is warmer than the surrounding land. 



In the present state of our knowledge, then, it appears that when the 

 temperature of the earth has been observed at a depth of some hundreds of 

 feet in any locality in Great Britain, and has not been accurately determined 

 at a less deptli, some knowledge of the rate of increase downwards may be 

 obtained by assuming provisionally that the mean temperature of the surface 

 is about a degree higher than the mean temperature of the air, supposing the 

 latter to be known. 



It is to be wished that the "Meteorological Society would, from the ample 

 materials in their possession, publish a map of annual isothermals for Great 

 Britain ; and the objects of this Committee would be greatly furthered by 

 an extensive scries of soil-temperature observations at the depth of about 

 3 feet. 



The Committee are anxious to carry into effect Mr, Hull's proposal (quoted 

 in their last Report) to bore down from the bottom of a deep mine ; and as 

 Hose-Bridge Colliery appears to be an eminently suitable locality for such an 

 operation, the Secretary has consulted Mr. Bryham respecting its practicability 

 and probable cost. Mr. Brj'ham's reply is that there would be no difficulty 

 in carrying out the proposal at Rose Bridge, that to make preparations and 

 bore 300 feet would, on a rough estimate, cost £150, and that the second 

 300 feet would probably cost about the same sum. 



The Committee would earnestly appeal to the liberality of the Association 

 to enable them to put this design in execution ; and they would remark that 

 the sooner it is carried out, the more valuable the results obtained will be, as 



