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James Clerk Maxwell
   
 
DOCUMENTI 
 
Lettera a LEWIS CAMPBELL
6 luglio  1849
 
 TO LEWIS CAMPBELL, Esq.

                                                                      Bannavie, 6th July [1849].
 

This being a wet night, and I having exhausted my travelling props, set to to write to you about what I can  recollect of my past history. It is curious that though the remembrance of ploys remains longer than that of home  doings, it is not so easily imagined after a short interval.

By imagining is here meant bringing up an accurate image of thoughts, words, and works, and not a mere  geographical summary of voyages and travels.

But to the point. Perhaps you remember going with my Uncle John Cay (7th Class), to visit Mr. Nicol in Inverleith    Terrace. There we saw polarised light in abundance. I purposed going this session but was prevented. Well, sir, I    received from the aforesaid Mr. Cay a "Nicol's prism," which Nicol had made and sent him. It is made of     calc-spar, so arranged as to separate the ordinary from the extraordinary ray. So I adapted it to a camera lucida,   and made charts of the strains in unannealed glass.

I have set up the machine for showing the rings in crystals, which I planned during your visit last year. It answers   very well. I also made some experiments on compressed jellies in illustration of my props on that subject The   principal one was this:—The jelly is poured while hot  into the annular space contained between a paper   cylinder and a cork: then, when cold, the cork is twisted round, and the jelly exposed to polarised light, when a   transverse cross, x, not +, appears with rings as the inverse square of the radius, all which is fully verified. Hip!

     etc. Q.E.D.
 
 

But to make an abrupt transcision, Forbes says, we set off to Glasgow on Monday 2d; to Inverary on 3d;   to Oban by Loch Awe on 4th; round Mull, by Staffa and Iona, on (5th), and here on 6th. To-morrow we intend    to get to Inverness and rest there. On Monday perhaps? to the land of Beulah, and afterwards back by Caledon.   Canal to Crinan Canal, and so to Arran, thence to Ardrossan, and then home. It is possible that you may get a  more full account of all these things (if agreeable), when I fall in with a pen that will spell; my present instrument
partakes of the nature of skates, and I can hardly steer it.

There is a beautiful base here for measuring the height, etc., of Ben Nevis. It is a straight and level road through a   moss for about a mile that leads from the inn right to the summit.

It is proposed to carry up stones and erect a cairn 3 feet high, and thus render it the highest mountain in Scotland.

During the session Prof. Forbes gave as an exercise to describe a cycloid from top of Ben Nevis to Fort William,  and slide trees down it. We took an observation of the slide, but found nothing to slide but snow.

I think a body deprived of friction would go to Fort William in a cycloid in 49·6 seconds, and in 81 on an inclined   plane. I believe I should have written the greater part of this letter to Allan Stewart, but I know not where he is, so   you get it, and may read it or no as you like.

We will be at home between the 15th and 22d of this month, so you may write then, detailing your plans and   specifying whether you intend to come north at all between this and November, for we would be glad if either you   or Bob would disturb our solitude.