My dear Sir –
I send you Secchi’s2 original paper,3 but will beg you to have the kindness to return it as soon as you have satisfied yourself that the diagram in the Phil Mag. is the same as in the Corr. Scien.,4 and the text the same.
The diagram5 does not appear to be well suited t[o] assist the conception; but of this I am & can be but an indifferent judge, because I am so familiar with the facts themselves – I take Secchi’s illustration to be this –
At Toronto (T) the end of the needle acted upon is (according to his view) the upper end or S. Pole – The sun in his progress from E. to W. (East to West) causes the S. pole of the needle to be at 20″ to the West of its mean position; at 2″ to the East; at 9½″ to the West; and at 15½″ to the East of its mean position.
At Hobarton6 (H) it is the N Pole (there the upper pole) which is acted upon, and the sun in his progress from E to W causes there the N. Pole to be to the East of its mean position at 20″; to the west at 2″; to the East at 9½, and to the west at 15½.
I repeat the illustration does not help me; but it possibly may others whose minds are in the state of Secchi’s – About the facts however there is no difficulty (at least I hope not because I am there the responsible party) – He gives my statement in my own words,7 and you or any one finds any difficulty in understanding these, pray tell me so.
You say that ‘the arrow head is what we call the North Pole of the needle’. I say nothing against that in a general way, but certainly Secchi does not [1 word illeg] his arrows to a needle at all. An index hand projecting from the vertical SW, to the right at Toronto and to the left at Hobarton at 20″, &c, would not have misled, as the arrow appears to have done.
If the arrows are to be regarded as needles, then the point of the arrow indicates at each station the pole which he conceives to act upon – i.e. the upper pole; i.e. the S. at Toronto, and the N. at Hobarton.
It is all clear in Secchi’s mind because his mind is imbued with his hypothesis.
Sincerely yours, | Edward Sabine.
RI MS JT/1/S/14
RI MS JT/1/TYP/4/1304
[6 November 1854]: LT’s typescript includes the date of 6 November 1854, though the original letter was not dated.
Secchi’s: Pietro Angelo Secchi (1818–78), an Italian astronomer and Jesuit priest, who served as Director of Observatory of the Collegio Romano from 1850 until his death. He was a pioneer of spectroscopy who focused much of his work on the sun.
original paper: see ‘Sulla maniera di determinare la flesione dei tubi nei grandi strumenti astronomici’, Corrispondenza Scientifica in Roma 3 (1855), pp. 209–21; 261–67. It had appeared in the July issue of the Corrispondenza Scientifica in Roma and was translated for the Phil. Mag. as, ‘On the Periodical Variations of Terrestrial Magnetism’, Phil. Mag. 8:53 (November 1854), pp. 385–99.
Corr. Scien.: Corrispondenza Scientifica in Roma was an Italian scientific journal.
The diagram: the diagram Sabine spoke of appeared on p. 394 of Secchi’s article (see n. 3).
Hobarton: Hobarton (now Hobart), Tasmania, Australia.
gives my statement … words: pp. 394–5 of Secchi’s article (see n. 3) quotes from E. Sabine, Observations Made at the Magnetical and Meteorological Observatory at Toronto in Canada, 2 vols (London: Longman, Brown, Green, and Longmans, 1845), vol. 1, p. 14.
Please cite as “Tyndall0997,” in Ɛpsilon: The John Tyndall Collection accessed on