124 JAMES CLERK MAXWELL. [CHAP. V. 



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 -f- , 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, 1 ' as 

 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 lona, 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. 



1 See below, p. 138, 1. 2. Forbes was extra-precise in articulation. 

 Hence the spelling. 



