COMPLETION OF THE NEW ROCK THERMOMETERS. 639 
And yet, in the first portion of my reply, it is not merely I that speak, but 
far more the spirit of that grand scientist of Scotland in the last generation,— 
JAMES Davip Forses. He, in his deep and earnest studies of nature, 
desired to obtain numerical expressions for certain Natural Philosophy 
constants ; such as, given the summer heat, the winter cold, and the daily 
variations on the surface of the ground, together with the physical rock 
below,—at what rate do those temperatures and variations of the same 
travel downwards towards the centre; the results being required accurate to 
the hundredth of a degree Fahr., and a fraction of a day as to time. 
The only mode of correctly ascertaining these data free from very large 
and possibly ruinous disturbances, was then well considered to be, the having 
thermometers large enough to allow of their bulbs being set in the heart of 
the rock, at every required depth, viz. 3, 6, 12, even 24 feet, while their scales 
were on the surface of the ground. 
The necessary expense was therefore most willingly incurred, though in 
the economical days of forty and more years ago; together with the labour of 
observing for many seasons. Not only too the Observatory set of thermo- 
meters, but two other sets like it, one at the Craigleith Quarry, and the other 
at the then Experimental Gardens. And these measures proved successful ; 
for the problem was at length solved by them; in a manner and with a 
completeness too, not only to satisfy Professor Forses himself,—after whose 
passing over a scieutific field, there was little enough left for any one else to 
glean—but to well content the Royal Society, Edinburgh, also. For the 
Society printed the Professor’s noble Memoir on the subject in their 
Transactions for 1845-46 (Vol. X VI.), and crowned it with a prize. 
Soon after the above clenching event, the other two sets of thermometers 
were reported broken ; and the question then came before me, in my official 
capacity at the Royal Observatory,— what shall be done with the one 
remaining set of rock thermometers there ? 
After consulting with Mr ALEXANDER WALLACE, the Assistant-Astronomer, 
who had carried out, under my predecessor, THomMAs HENDERSON’S, supervision, 
all the previous observations for Professor Forses from the first,—I decided 
that they should continue to be observed; largely because I believed them to 
be the best set of rock-thermometers in the world, and also because there is 
still an immense deal connected with the temperature of man’s planetary abode, 
which he has not mastered yet. So the observations were continued without a 
break, and before long another practical use did appear for them ;—thus,— 
The Transit Instrument in the Royal Observatory, Edinburgh, had been 
known to my predecessor to be affected with an annual fluctuation of level 
from East to West, nearly in accordance with the readings of a small thermo- 
meter under the floor of the building ; and there was a belief in the community 
