13 Ashley Place S. W. | Jan[uar]y. 11th 1861
Dear Tyndall.
If I understand you right you wish to show your class1 the way in which the motions of the magnet are recorded in our observatories by eye-observation.
And you purpose to exhibit to them first the motions of the magnet themselves, by reflecting a Dubosc lamp2 on a skreen3 from a mirror attached to the magnet—so far so well.
Your subject will then lead you into two divisions—First you will show them how the image of a scale which is fixed to the Telescope, & illuminated, is reflected by the mirror onto the field of the Telescope & so read off. This is Gauss’s4 original plan, and is used by us whenever the disturbances occur of so large amount as to make the substitution of a collimator & lens affixed to the magnet instead of a mirror an inadequate apparatus by reason of the collimator scale going beyond the limits of the field of the telescope, as it does sometimes even in England. You should therefore exhibit also a magnet furnished with a collimator scale & lens,—one of the 12 or 15 inch magnets will exhibit this very well, and will be quite comprehensible, by your explanation, without looking into the telescope—You will find the whole process by collimator minutely described by Lloyd in the Report of the Com. of Physics of the R.S. 18405—and the whole process of Gauss’s mirror method in the Sci Mem vol. 2. p. 37.6
I fear that I am forming a very uncertain notion of what your precise purposes are. But you must be more particular in defining your own purposes to enable me to help you more effectually, which I should delight in doing.
I think you will find a spare 12 or 15 inch magnet fitted with collimator & lens, & a telescope at Kew—& you will also find, a small magnet and a mirror, & a telescope furnished with the scale. Brooke7 has also (I doubt not) both if you do not find them at Kew.
Sincerely yours | Edward Sabine
RI MS JT/1/S/19
RI MS JT/1/TYP/4/1314
your class: probably Tyndall’s students on his course of general physics at the School of Mines.
Dubosc lamp: Louis Jules Duboscq (1817–86), instrument maker and inventor of the Duboscq lamp, an arc lamp. Tyndall bought these for demonstrations in his lectures. See, for example, letter 1646.
skreen: screen.
Gauss’s: Carl Friedrich Gauss (1777–1855), German mathematician and astronomer. Gauss was the first director of the Göttingen observatory in Germany, and was one of the principal figures in the international programme to systematically study the Earth’s magnetic field. Gauss developed a mathematical theory which correlated the data collected onto a model of the Earth’s internal magnetic structure. His theory rejected the notion, which had been previously held by Sabine, that the Earth’s magnetism could be explained by two magnetic axes, both in motion. Gauss also invented what he called the magnometer, an early type of magnetometer which measured the direction and strength of a magnetic field.
described by Lloyd in the Report of the Com. of Physics of the R.S. 1840: in the section entitled ‘Terrestrial Magnetism’ in the Royal Society’s Report of the Committee of Physics, including Meteorology on the objects of Scientific Inquiry in those Sciences (London, 1840), pp. 1–37.
Gauss’s mirror method in the Sci Mem vol. 2. p. 37: R. Taylor (ed), Scientific Memoirs (London: Richard and John E. Taylor, 1841), vol. II, p. 37.
Brooke: probably Charles Brooke (1804–79), surgeon and inventor of measuring instruments. He was a FRS from 1847, and President of both the Meteorological Society (1865–67) and the Royal Microscopical Society (1863–4 and 1873–4). Brooke was best known for his inventions of self-recording instruments, such as barometers, thermometers, psychrometers, and magnetometers which were adopted at the observatories at Greenwich, Paris, Toronto, and Cambridge, Massachusetts. These instruments would automatically register variations by means of photography (ODNB). See, for example, C. Brooke, ‘On the Automatic Registration of Magnetometers, and Other Meteorological Instruments, by Photography’, Phil. Trans., 137 (1847), pp. 59–77.
Please cite as “Tyndall1759,” in Ɛpsilon: The John Tyndall Collection accessed on