Queenwood College, | Stockbridge, | Hants. | 30th. July 1851
Dear Sir,
It would have afforded me great gratification to have made these magnetic experiments1 before you; but as the destinies seem disposed to deny me this pleasure, I take the liberty of forwarding you a few substances2 which you perhaps will be good enough to suspend in the magnetic field when your leisure permits.
No.1.3 contains two cylinders of bismuth; between the flat poles one sets axial, the other equatorial. Between the pointed poles when near, the former sets equatorial also, but on withdrawing the poles to a distance from each other it turns into the axial position. In this case the principal cleavage is transverse to the axis of the cylinder, as you can prove by trial with a knife; and I believe you will conclude that the cause of its setting equatorial between the near poles is due to the fact that the tendency of the mass to pass from stronger to weaker places of magnetic force overcomes the directive power of the crystal. If the mass were a sphere the powerful cleavage would always set equatorial, between both points and flat faces. This turning towards the axial line, as you are aware, is attributed by Plücker to a triumph of magnetism over diamagnetism; but I think you will see that it is on account of the more equable condition of the magnetic field permitting the directive action of the crystal to assert itself.
No.2. contains two bismuth plates; the magne-crystallic axis is perpendicular to the flat surface of each, but it will set equatorial. This has been brought about by compression between two plates of copper in a hard vice. Before compression the magne-crystallic axis set in both cases strongly axial.
No.3. contains a plate of compressed wax; it is diamagnetic, and the line of compression sets equatorial, thus causing the plate to set its length from pole to pole.
No.4. contains a crystal of carbonate of iron, and a model of the same, formed from the crystal when pounded into dust and sifted through linen. I think you will see that the deportments of both are so far similar as to be suggestive of a common origin. The dough from which the model is made was compressed in the direction of the optic axis.
No.5. contains a prism of carbonate of iron artificially made. suspended from the centre of one of its sides it will set axial – change the point of suspension 90° in the equatorial plane; it will set strongly equatorial. Between the near points, when they are not too strongly excited the prism suspended as in the latter case will set axial, between the distant points it will turn into the equatorial position. This is the phenomenon which Plücker attributed to the triumph of the optic axis force at a distance in the case of tourmaline, idocrase, and other magnetic crystals. In explanation of this I will merely say, that when the prism sets equatorial between the excited poles, the mass of dough from which it was taken was compressed in the horizontal line perpendicular to the axis of the prism – the line of compression sets axial and hence the prism itself equatorial. With regard to the turning round I believe you will see the analogy between this case and that of the bismuth cylinder, the one being recession and the other approach.
No.6. contains a bit of shale; suspended from one of its edges it sets axial, from the edge adjacent, it sets equatorial. This is similar to Plücker’s first experiment with the plate of tourmaline. I had a much finer piece of shale to show this experiment but it has unfortunately got broken.
It is with considerable reluctance that I introduce any personal affair of mine to your notice, and yet I am induced to do so at present. I returned from Germany, as you are aware, a few weeks ago and entered a situation here. I am teacher in this college and when our work commences I expect to be occupied about 7 hours a day. My salary is £150 a year, rooms in the college and board; and I find the Principal and his family willing to do all they can to render my life agreeable. The institution is a private one, and with regard to its durability I am unable to utter a word. The boys whom I have to teach are young, and I shall be engaged with them at the lower mathematics, such as Euclid, Algebra perhaps to quadratic equations, and a little trigonometry, and elementary physics. I shall have to lecture twice a week, but to suit my audience must confine myself to elementary matters. There is danger in retrogression in such a position, and there is also the everlasting consciousness of want of permanency. I think this is a sufficient account of my present position.
In the last two numbers of the Athenaeum4 I find an advertisement stating that in the university of Toronto there are 6 professorships now vacant at the annual salary of £350 Halifax currency;5 one of these is the professorship of Natural Philosophy It occurred to me as I read the advertisement that I ought to make application for the post, and after turning this matter round in my mind I concluded that the wisest plan would be to solicit your advice, and this conclusion was confirmed by my friend Dr. Francis of the Philosophical Magazine. Nobody can be more sensible than I am how slender are the grounds upon which I can justify this liberty, and had I been left to my own unaided cogitations I should hardly have attempted it. But to return; if both choices were before me I should prefer remaining in this country to going to Canada – not that I lay stress upon locality any further than that I like to be near men of science. But I dont know my chances in England and hence I think it unwise to allow an opportunity like the present to escape me. To settle myself down at Queenwood, even granting it permanent, would be to sacrifice an object for which I have battled harder than anybody knows, and that is to approve myself a worker in science. Seven hours plus meal times and other contingencies, plus the time to depolarize the intellect6 after having been engaged with other matters is a heavy subtraction from the day. I ask your counsel in this state of things – something doubting I must confess, for I know I have no right to expect it – I have already written to Magnus and Poggendorff7 for testimonials so that if you advise the step I shall be ready to take it promptly.
I remain dear Sir | Most faithfully & respectfully yours | John Tyndall
Prof. Faraday F.R.S. | &c &c
RI MS JT/2/12/4009–4012
Transcript Only
these magnetic experiments: letters 0501, 0506 and 0507 all refer to experiments performed or described in presentations by Tyndall at the Ipswich BAAS meeting. The letters do not make clear what experiments Faraday missed and when Tyndall had performed or expected to perform them. Given Faraday’s interests, the experiments must have related to his presentation ‘On Diamagnetism and Magnecrystallic Action’, a paper Faraday attended (letter 0501).
forwarding you a few substances: the substances described in the succeeding experiments, No. 1, two cylinders of bismuth and so on, to No. 6, the bit of shale.
No. 1: In the transcript, the six numbered paragraphs are formatted as hanging paragraphs but not consistently. We have made the formatting consistent.
last two numbers of the Athenaeum: letter 0504, n. 3.
Halifax currency: see ‘Note on Money’.
depolarize the intellect: Tyndall had learned to use physical metaphors for mental processes from his teacher, John Conwill (see Volume 1).
written to Magnus and Poggendorff: letters missing. Tyndall mentioned the same requests in letter 0504.
Please cite as “Tyndall0505,” in Ɛpsilon: The John Tyndall Collection accessed on 27 April 2024, https://epsilon.ac.uk/view/tyndall/letters/Tyndall0505