SUPPLEMENTARY REPORT ON METEOROLOGY. 73 
of different observations on the rate of progress of heat into the 
soil, especially as depending on its geological character, a com- 
pact sonorous sandstone transmitting heat at the rate of one 
foot in four days, whilst in loose sand (the same ingredient) it 
required 6:2 days. The following tables illustrate the varying 
retardation and proportionate diminution of amplitude (or range) 
at different depths*. 
s8 
a Maximum. Minimum. Range. 
Se 
eae ee eel Bayt d Delos bye ifs te dowiasne ed BS oa | Sab Babe tenes tecgt 
Ki Trap. Sand. Sandst. Trap, | Sand. Sandst. Trap. ;} Sand, | Sandst. 
3 | Aug. 5| Aug. 2| Aug, 7 || Mar. 6] Feb. 28! Feb. 23 ||9° -67c|11°-03c|9° -67c 
6 | Sept. 1| Aug. 25| Ag.19 | Mar. 20 | Mar. 22 Mar. 3 \6° "12 | 8°-05 |7° -68 
12 | Oct. 15| Oct. 8] Sept.14 || Apr. 25 | Apr. 22 | Mar. 26 |/2° -85 | 4°-03 |5° -01 
24 | Jan, 6} Dec.31| Nov. 6 | July 15} July 1} May 12 |/0°-75 | 1°-00 |2° -20 
102. What we have now stated respecting annual variations of 
temperature, is found to be true, mutatis mutandis, for diurnal 
ones. Theory shows that the depth at which periodic fluctua- 
tions sensibly vanish should be (ceteris paribus) as the square 
roots of their periods, and this is found to be nearly the case in 
point of fact; the diurnal oscillation being nearly as insen- 
sible at a depth of three or four feet, as the annual one is at nine- 
teen (or / 365) times the depth, or at 60 or 70 feett. M. Que- 
telet has made a most extensive series of observations at small 
depths, and he finds the diurnal heat-tide to penetrate at the 
rate of 1 decimetre (4 inches) in 2°8 hours nearly, in the month 
of Marchf. 
103. We now hasten to state a few other conclusions which 
have been attempted to be drawn from the very important class 
of observations of which we have recently spoken. Did we 
possess, in the actinometer or any other instrument, the 
means of measuring the actual force of sunshine in any place at 
a given moment, insuperable difficulties would yet arise to the 
determination of the very important questions, “‘’To what extent 
does the direct solar influence actually contribute to produce 
the climate we enjoy?” and “ What would be the temperature 
of our globe without the sun?’’ It is difficult or impossible 
for us to take cognizance of the perpetually fiuctuating amount 
of solar heat, and to sum up the discontinuous amount of it du- 
‘ting the year, allowing for intervals of darkness, atmospheric 
_ * These numbers are (excepting the epochs of minima, which are but two 
years) amean of three years. The temperatures are centigrade. 
+ Quetelet, wt supra, p. 72. { Ibid, p. 68. 
