June 21. 1861.
Dear Tyndall.
I find an account of the comparative retardation of the Pendulum in Hydrogen Gas and Atmospheric Air in the Phil Trans. for 1829 p 227. (Expt Feby 9 & 10)1—I made similar experiments in other gasses, but cannot at the moment refer to the account of them. (Olefiant Gas2 was one of those experimented upon.)
On the subject of the facts of the solar diurnal magnetic variation you will find the facts tolerably lucidly stated in the Introduction to the 2d vol of the St Helena Obsns p.p. cxvii to cxxi.3
You asked me some time ago about the annual variation of the Total magnetic force of the Earth.
You will find in page CXXIV of the 3d vol. of the Toronto Obsns,4 the results showing that at that station in the Northern hemisphere the Total Force is decidedly greater in the months of November to February than in May to August—And in the 1st vol, Hobarton p. lxxxvi5 the conclusion that at that station in the Southern hemisphere the Total Force is also greater from October to February than from May to August. The latter conclusion was drawn from the Obsns which I possessed when that vol. was printed: I have subsequently received more from Hobarton, and have them now preparing for publication.
I purpose to enter then more fully into the question as regards Hobarton, tho’ I have no reason to suppose that the conclusion will be other than the one referred to in vol. 1—but it will probably be in my power to state somewhat more precisely for Hobarton (as I have done for Toronto) the approximate precise value of greater intensity of the Earths Magnetism in December than in June.
faithfully yours | Edward Sabine.
RI MS JT/1/S/23
RI MS JT/1/TYP/4/1320
in the Phil Trans. for 1829 p 227. (Expt Feby 9 & 10): E. Sabine, ‘On the Reduction to a Vacuum of the Vibrations of an Invariable Pendulum’, Phil. Trans., 119 (1829), pp. 207–35.
Olefiant Gas: ethene, a gas that was of great interest to Tyndall in his radiant heat experiments, as it was a strong absorber of heat.
Introduction to the 2d vol of the St Helena Obsns: Observations made at the Magnetical and Meteorological Observatory at St. Helena with discussions of the observations at St. Helena, The Cape of Good Hope, The Falkland Islands, Carlton Fort in North America, and Pekin. Vol. II. 1844 to 1849 (London: Longman, Brown, Green, and Longmans, 1860), pp. cxvii–cxxi.
3d vol. of the Toronto Obsns: Observations made at the magnetical and meteorological observatory at Toronto in Canada. Vol. III. 1846, 1847, 1848 (London: Longman, Brown, Green, and Longmans, 1857), p. cxxiv.
1st vol, Hobarton: Observations made at the magnetical and meteorological observatory at Hobarton, in Van Diemen Island and the Antarctic Naval Expedition. Vol. I. Commencing with 1841. With abstracts of the observations from 1841 to 1848 inclusive (London: Longman, Brown, Green, and Longmans, 1850), p. lxxxvi. Sabine appears to have given an incorrect reference. Variations in the Total Force are described on pp. lxvii–lxxii.
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