My dear Father,

I received the book this morning & have just turned over the pages & looked at the wood-cuts.¹ I am rather disappointed to see how carelessly they are printed; they are not comparable to the proofs I saw at home. I notice a slight mis-statement Fig 149 was not from a photo. And surely 147 was not either² Fig 162 there was a photog. but so blurred that I drew the left hand one almost entirely from the plant as I believe. The right hand one was drawn entirely from nature.³ If I am not right in my memory of this I shall be enormously surprized & especially I remember the right hand fig. of 149 because it was the hardest one which was done entirely from nature. However this is all very unimportant.

I have been going on with ripple-marks & can now produce them in a flat bath with almost the regularity of a mathematical figure with wave lengths varying from perhaps 3 or 4 inches to $\frac{1}{2}$ inch.⁴ I can produce no ripple mark with currents & I believe that when ripple is produced along with current the current must be slow & wave motion must be going on on the surface   I find a rough formula for wave length of ripple-mark as a multiple of the greatest velocity of the water relatively to the sand in the oscillatory motion. Also no ripple is produced if this max: vel: is less than $\frac{1}{2}$ a ft per sec. & again none if greater that 1.2 ft per sec. There is a marked tendency to sort the sand along the crests of the ripples.

I am inclined at present to think it is a complex affair partly depending on the rates at which different sized grains acquire the velocity of the water moving past them & partly on my previous theory of the sand being elongated   I fancy I shall be able to reduce my apparatus so as to make absolutely regular ripples. They already are good. I got the other day 66 ripples round the bath with only one partially broken. The more I see the more I think Lyell utterly wrong.⁵

I am in despair about my astronomy. I am in this position that I must refer to my theory in its bearing on the solar system as a whole that I can not make any problem which shall reasonably represent the case & that I must write a sort of general discussion which will I fear be very unsatisfactory & will be more speculative than I like, and moreover I fear the outcome of the whole to any one who does not read thoro’ly will be more unfavourable to the theory than I am convinced it sh^d. be.⁶

I have been rather better for about a week now & have worked spasmodically. My cold, quà cold, has much subsided, tho’ it is at me pretty vigorously in the usual way.

Arthur Balfour has been here for a few days, but he had’nt got very much politics to tell.⁷ I dined last night at Horaces & met Miss Gladstone & afterwards we went to the Amateur Dramatic play.⁸ We went down in the tram-car in an awful crowd with Ida sitting on Miss G’s lap, & then walked on thro’ the rain   We had a fearful storm of wind & rain last night, all night thro’. & only stayed at the play for two or three acts. It was’nt at all good & I had seen it before—.

A.B. wants Horace to do another little job at Whittinghame but I don’t think it will be much—⁹ It is something wh H. had suggested before.

I am dining at F. Balfour’s tonight to meet Evans (J. E’s son) who is come back from Bosnia & Ragusa for a short visit in England. I think you read his book.¹⁰

Your affec. son | G H Darwin