x 
Proceedings of the British Association. 333 
this view. The result obtained by him tended to confirm it very 
unequivocally ; and so did another series, made the same year in 
Dolcoath mine, by John Rule, Jr. one of the superintendents. 
Many other individuals have since at the request of Mr. F., carri- 
ed on similar observations in different mines, all showing that the 
subterranean temperature increases in some proportion to the 
pth of the stratum. The tables of observations given in the 
Report confirm Mr. F'ox’s previous views, that the rate of increase 
is not so considerable at deeper excavations as at those which 
are shallower.—Mr. Eaton Hodgkinson read a paper on the tem- 
perature of the earth in the deep mines near Manchester.—Prof, 
Forbes thade his report on the temperature and conducting pow- 
ers of different strata. The results agree substantially with those 
reported by him last year. 
Sir D. Brewster read a report on the Phenomena and cause of 
musce volitantes. As this paper was illustrated with several draw- 
ings, and contained minute experimental details, it is not easy to 
give a popular account of it. The following are the principal re- 
sults. 1. In persons of all ages, and with the most perfect eyes, 
transparent filaments or tubes exist in the vitreous humor, and at 
different distances from the retina. 2. These filaments float in 
the vitreous humor, moving about with the motion of the head. 
3. These filaments are seen by means of their shadows on the 
retina, and are most distinctly visible in divergent light, their 
shadows being bounded by fringes produced by diffraction or in- 
Hexion. 4, The real musce, resembling flies, are knots tied, as 
were, on these filaments, and arising from sudden jerks or mo- 
Hons of the head, which cause the long floating filaments to 
*verlap and run into knots. 5. By making experiments with the 
in all positions, and determining the limits of the motions 
of the muses, by measuring their apparent magnitude, and pro- 
ducing double images. of them by means of two centres of di- 
Vergent light, the author was able to determine their exact place 
0 the vitreous humor, and to ascertain the important fact that 
the Vitreous humor in the living human eye is contained in cells 
- limited magnitude, which prevent any bodies which they con- 
0 from passing into any of the adjacent cells. The author 
ee with the following observations: ‘I have welt thus 
ong on the Subject of musce volitantes, not only because it Is an 
sd ." one, but also on account of its practical utility. Mr. 
7 My NO. 2.—Jan.—-March, 1841. © 43 
