64 Dr. H. Franklin Parsons on 



range of only 21.1°, as against a range of 34 -1° at 1 ft. and 72° 

 in the air. 



4. That the movement of the 4 ft. thermometer was much 

 more equable than that of the 1 ft. one ; the former exhibiting 

 few fluctuations, and never a difference of so much as 3° between 

 the readings of successive weeks, whereas the latter exhibits 

 many ups and downs, and sometimes differences of over 7° in 

 successive weeks. 



5. That in its movement the 4 ft. thermometer lags behind 

 the 1 ft. one, being below it in spring and summer, and above it 

 in autumn and winter. 



The results, so far as they go, are in accordance with the 

 vastly more extended observations made at Greenwich Observa- 

 tory during the 27 years (] 847-73), and at depths ranging from 

 one inch to 8 metres =25-6 ft. The results of these observations 

 are shown as monthly means on another diagram. 



The mean yearly temperature of the air during the period 



was 49-43° 



Of the earth at one inch depth, 51-97° 



„ „ 3-2 ft. „ 51-19° 



„ 6-4 ft. „ 51-69° 



„ 12-8 ft. „ 50-89° 



„ 25-6 ft. „ 50-56° 



The movement of the temperature at one inch depth was 

 nearly parallel to that of the air, but it was higher throughout 

 by 2° in winter and 3° in summer. At the greater depths the 

 movement of the temperature was retarded in proportion to the 

 depth. Thus, while the highest monthly mean in the air was 

 attained in July, that of the earth at 3-2 ft. was attained in 

 August, at 6-4 ft. in August and September, at 12-8 ft. in 

 September and October, and at 25-6 ft. in November and 

 December. Conversely, the lowest monthly mean was attained 

 in the air in January, at 3-2 ft. depth in February, at 6-4 ft. 

 depth in February and March, at 12-8 ft. in March and April, 

 and at 25-6 ft. in May and June. Thus, owing to the bad con- 

 ducting properties of the earth, the annual heat-wave takes four 

 or five months to reach to a depth of 25 ft. 



The temperature also becomes more equable in proportion to 

 the depth. Thus, while the monthly means of the air tempera- 

 ture vary through a range of 24°, those of the thermometer at 

 3-2 ft. range through 21°, at 6-4 ft. through 15°, at 12-8 ft. 

 through 9°, and at 25-6 ft. through little more than 3°. At a 

 greater depth it may be expected that we should meet with a 

 practically equable temperature, unaffected by the seasons, and 

 not far distant from the mean temperature of the locality. 



Our distinguished member, Mr. Baldwin Latham, tells me 

 that he has for a number of years made observations with earth 



