runs.  Brunel and other people had arrived in the night.  And we have been to Darlington and back, with a large party in our experimental train.  George Arthur Biddell rode on the engine as representing me.  But the side wind was so dreadfully heavy that, as regards the wants of the case, this day is quite thrown away.  We have since been to lunch with Vernon Harcourt (Mrs Harcourt not at home) and then went with him to look at the Cathedral.  The Chapter-house, which was a little injured, has been pretty well restored:  all other things in good order.  The Cathedral looks smaller and lower than French cathedrals.  Now that we have come in, the Lord Mayor of York has just called to invite us to dinner to-morrow.—­I propose to George Arthur Biddell that he go to Newcastle this evening, in order to see glass works and other things there to-morrow, and to return when he can.

I think that I can persuade Barlow to stop to see the experiments out, and if so I shall endeavour to return as soon as possible.  The earliest day would be the day after to-morrow.

* * * * *

The following extract is from a letter written to Mr Murray for insertion in his Handbook of France, relating to the Breakwater at Cherbourg, which Airy had visited during his journey in France in the autumn of this year.

ROYAL OBSERVATORY, GREENWICH,
1845, Oct. 8th.

My opinion on the construction I need not say ought not to be quoted:  but you are quite welcome to found any general statement on it; or perhaps it may guide you in further enquiries.  To make it clear, I must speak rather generally upon the subject.  There are three ways in which a breakwater may be constructed. 1.  By building a strong wall with perpendicular face from the bottom of the sea. 2.  By making a bank with nothing but slopes towards the sea. 3.  By making a sloping bank to a certain height and then building a perpendicular wall upon it.—­Now if the 1st of these constructions could be arranged, I have no doubt that it would be the best of all, because a sea does not break against a perpendicular face, but recoils in an unbroken swell, merely making a slow quiet push at the wall, and not making a violent impact.  But practically it is nearly impossible.  The 2nd construction makes the sea to break tremendously, but if the sloping surface be made of square stone put together with reasonable care there is not the smallest tendency to unseat these stones.  This is the principle of construction of Plymouth Breakwater.  In the 3rd construction, the slope makes the sea to break tremendously, and then it strikes the perpendicular face with the force of a battering ram:  and therefore in my opinion this is the worst construction of all.  A few face-stones may easily be dislodged, and then the sea entering with this enormous force will speedily destroy the whole.  This is the form of the Cherbourg Digue.

From this you will gather that I have a full belief that Plymouth Breakwater will last very long, and that the Digue of Cherbourg, at least its upper wall, will not last long.  The great bank will last a good while, gradually suffering degradation, but still protecting the Road pretty well.