TRACT 26.

MEAN DENSITY OF THE EARTH.

6S

to that of water, of sand, of clay, of chalk, of stone, or ofsome of the metals ? For, according to the matter, or differ-ent sorts of matter, of which it is formed, and according as itis constituted with or without large vacuities, its mean densitymay be greater or less, and that in a degree which is not cer-tainly known. A considerable degree of accuracy in thispoint could perhaps only be obtained by a close examinationof the internal structure of the hill. • And the easiest methodof doing this would be to procure holes to be bored, in seve-ral parts of it, from the surface to a sufficient depth, after themanner that is practised in boring holes to the coal mines fromthe surface of the ground ; for by such operation it is knownwhat kind of strata the borer has passed through, togetherwith their dimensions and densities. The proper mean amongall these would be the mean density of the hill, as comparedto water, or to any other simple matter; and thence we shouldobtain the comparative density of the whole cr.rth with respectto water. But, in the present instance, we must be satisfiedwith the estimate arising from the report of the external viewof the hill; which is, that to all appearance it consists of anintire mass of solid rock.

The following is an extract of a letter from a learnedgentleman, Mr. Duncan Macara of Fortingal, who wrote theaccount of the parish in which the mountain is situated, torthe use of Sir John Sinclair’s Statistical Work. “ As to themountain, says Mr. Macara, I have been at the top of it, andround the bottom frequently, but have not observed any thingparticular on it, that was not to be found in the mountains altaround, some of which arc higher than it. I have seen gen-tlemen, who made natural history their study, who were ofthe same opinion, and they examined it narrowly. On thenorth side it is covered with moss, generally about two orthree inches, on which grows heath, and in some parts a littlegrass. On the south and west are cairns, of large and smallstones, up to the summit. How they came to be so high, isa question, if an earthquake was not the cause. The stone,of which the mountain seems to be one solid mass, is the same