Philosophical Transactions, 167 
10. A Letter from John Pond, Esq., Astronomer Royal, to Sir 
Humphry Davy, Bart., P.R.S., relating to a derangement in 
the Mural Circle, at the Royal Observatory. 
This letter is dated “‘ November, 1821,” and as the amount 
of the error, and the correction which should be applied to the 
observations made within the two preceding years, have been 
already stated by the Astronomer Royal, in the Preface to the 
Greenwich Observations for 1820, it is not necessary to enter 
into the history of the derangement of the mural circle, which 
Mr. Troughton has long ago rectified. 
11. On the Finite Extent of the Atmosphere. By William Hyde 
Wollaston, M.D., V.P.R.S. 
After adverting to the hypothesis of the limited divisibility of 
our atmosphere, and to that of its unlimited expansion, Dr. 
Wollaston observes, that, in the former case, it may be pre- 
sumed to be peculiar to our planet, but, in the latter, to per- 
vade all space, where it would not be in equilibrio, unless the 
sun, moon, and planets possessed their respective shares of it, 
condensed around them in degrees dependent upon the force 
of their respective attractions, except where other kinds of matter 
or unknown powers may be supposed to interfere. He then 
remarks, that though we have not the means of ascertaining 
the extent of our own atmosphere, those of other planets are 
nevertheless objects for astronomical investigation, and that it 
deserves consideration whether, in any instance, a deficiency 
of such matter can be proved ; and whether, from this source, 
any conclusive argument can be drawn in favour of ultimate 
atoms of matter in general. From observations of the passage 
of Venus near the Sun, in superior conjunction in May, 1821, 
made by Dr. Wollaston and Captain Kater, for three days and 
a half before and after the conjunction, no retardation of the 
passage of the planet, such as would occur from increasing re- 
fraction, could be perceived, and in consequence no evidence 
obtained of the existence ofa solar atmosphere. Dr. Wollaston 
then mentions the occultation of Jupiter’s satellites by the body 
of the planet, the approach of which, instead of being retarded 
by refraction, is regular, till they appear in actual contact ; 
here, therefore, it is evident there is not that extent of atmo- 
sphere which Jupiter should attract to himself from an infinitely 
divisible medium filling space ; the universal prevalence, there- 
fore, of such a medium cannot be maintained. On the contrary, 
all the phenomena accord with the supposition, “ that the 
earth’s atmosphere is of finite extent, limited by the weight of 
ultimate atoms of definite magnitude, no longer divisible by 
repulsion of their parts.” 
