From Thomas Archer Hirst   Decr 24th/55

Broughton | Dec^r 24^th/55

My dear John,

Thanks for your kind brotherly letter¹ which I read several times over. No failings of yours will ever overshadow my remembrance of you or ever affect the relation which always has and I am sure always will exist between us. I am almost sorry I ever mentioned your occasional manner of argument seeing you have thought so much about it. I do not think I should have done so had I alone noticed it, but within the last six months I have spoken to three or four people about you, good enough people in their way although incapable of seeing much further than mere failings, and I felt rather sorry to hear them express opinions or rather attribute qualities to you which were far below you. For my own part I am always too conscious that whatever you have to say is well worth hearing and considering to think much about the manner in which it is said. I know your heart and your motives far too well, to let any peculiarity of manner annoy me. But I might as well tell you that I have heard some of these good people² call you conceited, vain, pretentious and so forth. They do so it is true because they are unable to appreciate your character and are only able to fasten on a few superficial peculiarities of the same, and they are only worth listening to except for the purpose of attending to such little peculiarities of manner which if liable to misinterpretation had better be altered than not. But I have already bothered you too much about so trivial a subject. I should say there is not one of us who is not similarly talked about and with far more justice. The fact is I meet with so few who are not great admirers of you and I am so anxious that every body should be so that these few exceptions caused me to think more than usual about such scandal, and perhaps set me on the alert to see if there was any ground for their objections. As far as I am concerned I hope you will continue to be the same John Tyndall to me as you always were, I hope the welding will never weaken and that the conviction that you have in me as firm a friend as ever will cheer you as you grow older. For myself I am proud of your strength and of your successes. You may rest assured every new victory of yours is closely watched by me and rejoiced over as if it was my own. Go on John and God bless you.

The memoir³ you have sent me is a valuable one and in my opinion well worth publication in the Phil. Mag. Is it similar to the one you have sent to the R. S.? After reading it over carefully I have only one or two suggestions to make. I think it would be best to be a little more explicit or complete on page 13. I would take more pains to shew that a disc

[Figure XVI]

suspended from its centre a behaves as if it were a neutral body with a magnet or diamagnet placed along its axis bc. For as you have shewn this is a very important point. In your fig 2 you only consider two directions through the crystal. I think it would be better to mention all the intermediate directions.

If the magnetization along any line through a crystal is greater the less the angle it makes with the line of greatest magnetization. Then by comparing any two lines hi and jk equally inclined to the direction of the resultant of magnetic force it is clear that the magnetization along hi would be greater than along jk because the angle hab is less than the angle kab. The same being true of all lines in the quadrants daf and gae when compared with the corresponding lines in the quadrants fae and dag. The couples acting on the former would be greater than those acting on the latter and the crystal would turn as if a resultant couple were applied to the axis bc.

The explanation of Faraday’s experiment with the sulphate of iron turning on a silken axis is very good indeed. With reference to your fig. 9 it would be best to state that the centre of the sphere ought to be placed nearly in the line of motion of the pole n. As far as the disposition shewn by your figure is concerned your explanation is very clear and precise, but it may possibly be thought to depend too much upon the figure by which the eye is apt to be misguided with respect to directions when actual distances are not given or plotted to a scale. With respect to the explanation referring to your fig. 10. It would be more complete if you were to mention the effect of the pole N on the other axes in the bar besides the extreme one ns. It is true by so doing your explanation would be more complicated, but it would be more satisfactory to your readers to know that you had considered the effect of the pole on all parts of the bar.

The memoir is an exceedingly interesting one and as usual very clearly written, it is very pleasing to see how all Faradays and Plückers results paradoxical as they appeared fall under the general & simple rule.

Yours affectionately | T. A. Hirst.

RI MS JT/1/H/221