REMARKS ON SURFACE TEMPERATURE. 



117 



In further elucidation of this subject, observations were made during 

 August and September on the cooling effect of radiation from the lead cover- 

 ing the roof of our Museum. The results noted by Mr. Newcombe, as com- 

 pared with those in the shed adjoining in which our thermometers are hung, 

 were as follows : — 



o o 



The mean minimum of 24 nights in August was in shed 58-0 on lead 51 '5. 



30 „ September „ 50-8 „ 43-9. 



Showing an average cooling effect of 6-5° in August, and 6-9° in September. 



The minima of the nights on which the difference was 8o or more were : — 



Aug. 16 Shed 60 Lead 52 Sept. 2 Shed 54 Lead 46 



The influence of radiation in this case is not materially different from 

 that on grass, but the conduction of heat from the earth is much more 

 direct in the latter situation and renders exact comparison difficult. 



This conduction, as a condition of different soils, was, many years ago, 

 submitted to elaborate inquiry by Mr. Whitley ; and the results are recorded 

 in the Journal of the Bath and West of England Society, (Vol. Ill, pages 

 136, 137). Of these valuable and interesting observations I must content 

 myself with a very brief summary. They were made at Alverton, near Truro, 

 the seat of the late Mr. W. M. Tweedy, who kindly furthered them. Four pits 

 about 2 feet deep and 2 feet wide were dug in good healthy garden loam. 

 The first was filled with pure fine siliceous sand ; the second with garden 

 loam ; the third with yellow clay from the clay- slate ; the fourth with well 

 worked peat. The bulb of the thermometers was placed 4 inches below 

 the surface, in the centre of each pit ; and another thermometer was placed 

 in the same manner under the turf of the short grass of the lawn. The 

 thermometers were read in the morning when the temperature of the soil 

 was lowest, and again in the evening when it was highest. The table has 

 been deduced from all the observations, and is the result of about 5000 

 readings of the thermometers. The record extends from April 1852 to August 

 1853. The garden loam shewed a power of receiving and retaining heat 

 superior to that of any other naked soil. Siliceous sand did not come up to 

 the expectations formed of it. Clay maintained a bad preeminence for 

 coldness, but improved, by the good drainage, in the second year. The tem- 

 perature of the Peat was nearly equal to the garden loam, although naturally 

 wet and cold. 



As illustrative of the several seasons, I may give the results for Novem- 

 ber in the former year, and for February, April, and August in the latter :— 



I 3 



