EIGHT YEARS OF THE NEW EARTH-THERMOMETERS. 291 



Now the old thermometers had greater increases; thus, taking the period 1856-60 — 



when t x = +0°-89, tf= + 0°-60, f= + 0°-26, and £ 4 = 0. 



Their depths were indeed rather greater than those of the new Thermometers; but 

 even if we reduce these results by simple proportion to the lesser depth of the new 

 Thermometers, the above increases only become— 



for old ^ = 0° 74, t 2 = 0°-50, ^ = 0°-15, and * 4 = 0. 



Hence this is the first decided difference of results between the old and the new 

 Thermometers; or the new ones have less increase of readings for the same increase of 

 depth; and as it was never shown why the old ones had so much rise of temperature, the 

 result is so far rather satisfactory for the strength, and capacity to resist pressure on the 

 bulbs, of the new ones. 



But there is a greater apparent difference in the absolute temperatures indicated for 

 the earth-crust on the Calton Hill by the two sets of instruments. For the new Earth 

 Thermometers give for the mean of the annual means from 1880 to 1887, 



new £ 1 = 46°'29, £ 2 = 45°-93, ^ = 45°'83, and t i = A5°-77; 



while the old earth Thermometers in the last 5 years, 1856-60, of their complete existence 

 (Shaving been broken by the frost in the severe winter of 1860-1) gave, when reduced 

 to the slightly lesser depths of the new earth-Thermometers, 



* 1 = 47°-28, £ 2 = 47°'04, £ 3 = 46°'69, and £ 4 = 46°-54. 



But when further reduced to the colder temperature of the earth-surface at the epoch 

 of 1880-7, that is by o, 76 — as given by the smaller publication of the Meteorological 

 Society of Scotland, per the Registrar General of Births, Deaths, &c, in Scotland— -for 

 the " Towns " stations only, by the successive annual means of mean shaded air tempera- 

 ture, taken out for each component year, of the two groups of years concerned; the 

 derived, or old 



t 1 becomes = 46°-52, i 2 = 46°-28, £ 3 = 45°-93, and £ 4 = 45°78, 

 in plaee of, as the new 



* 1 = 46°'29, £ 2 = 45°-93, £ 3 = 45°-83, and £ 4 = 45°77, 

 or the differences are reduced to 



£' = 0°-23, £ 2 = 0°-35, £ 3 = o '10, and ? 4 = 0°'01, 

 where the old and the new earth-thermometers agree to 0°'01 at the surface of the 

 ground, but disagree to nearly 0°*30 at the lower thermometers; in the direction however 

 of indicating an abnormal excess of apparent temperature, but perhaps of real bulbs 

 bending in, for the older instruments. A result very probably to be considered creditable 

 to the late deceased optician, Thomas Wedderbtjrn ; but raising some special questions 

 in the future as to the increased means required of testing the index errors of even the 

 deepest Thermometers from time to time in some absolute instrumental manner, in spite 

 of their being buried more than 20 feet deep. 



