THE FIGURE OF THE EARTH. 31 



Hutton on Shehallien, near Blair- Athol, in Perthshire ; to 

 the comparison of pendulum lengths on a plain lying at an 

 elevation of 6000 feet and at the level of the sea (as for 

 instance Carlini's observations at the Hospice of Mont Cenis, 

 and Biot and Mathieu's at Bordeaux); and lastly to the deli- 

 cate and thoroughly decisive experiments undertaken in 1837 

 by Reich and Bailey with the ingeniously constructed torsion- 

 balance which was invented by John Mitchell and subse- 

 quently given to Cavendish by Wollaston. 26 The three 

 modes of determining the density of our planet (by vicinity 

 to a mountain mags, elevation of a mountainous plateau, and 

 the balance) have already been so circumstantially detailed 

 in a former part of the Cosmos (vol. i, p. 158), that it only 

 remains for us to notice the experiments given in Reich's 

 new treatise, and prosecuted by that indefatigable observer 

 during the interval between the years 1847 and 1850. 27 



chytic dome of Chimborazo. South-south-east of this mountain, near 

 the Indian village of Calpi, lies the volcanic cone of Yana-urcu, which 

 I carefully investigated in concert with Bonpland, and which is cer- 

 tainly of more recent origin then the elevation of the great dome- 

 shaped trachytic mountain, in which neither I nor Boussingault could 

 discover anything analogous to a crater. See the Ascent of Chimborazo 

 in my Rhine Schriften, Bd. i, s. 138. 



26 Baily, Exper. with the Torsion Rod for determining the mean density 

 of the earth, 1843, p. 6; John Herschel, Memoir of Francis Baily, 

 1845, p. 24. 



07 Reich, Neue Versuchemit der Drehwage, in iheAlkandl. dermathem. 

 physischen Classe der Ron. Sdchsischen Gesellschaft der Wissenschaften zu 

 Leipzig, 1852, Bd. i, s. 405, 418. The most recent experiments of my 

 respected friend Professor Reich, approximate somewhat more closely 

 to the results given in Baily's admirable work. I have obtained the 

 mean 5.5772 from the whole series of experiments: (a) with the tin 

 ball and the longer thicker copper wire, the result was 5.5712, with a 

 probable error of 0.0113; (b) with the tin ball, and with the shorter 

 thinner copper wire, as well as with the tin ball and the bi-filar iron 

 wire, 5.5832, with a probable error of 0.0149. Taking this error into 

 account, the mean in (a) and (b) is 5.5756. The result obtained by Baily, 

 and which was certainly deduced from a larger number of experiments 

 (5.660), might indeed give us a somewhat higher density, as it obviously 

 rose in proportion to the greater lightness of the balls that were used 

 in the experiments, which were either of glass or ivory. (Reich in 

 Poggend. Annalen, Bd. Ixxxv, s. 190. Compare also Whitehead Hearn 

 in the Philos. Transact, for 1847, pp. 217229.) The motion of the 

 torsion balance was observed by Baily by means of the reflection of a 

 acale obtained from a mirror, which was attached to the middle of th 



