Dear M^r Whewell.—

Will you have the kindness to answer me the following question. If you would tell me whether I am right or wrong, when we meet at the Geological Council, I should be very much obliged.— I have been much interested on the subject of earthquake waves.— it appears to me, that all that happens is merely a consequence of a common undulation travelling from a little distance in the offing; after stating this case, I have added the following sentence, which I inferred from what you said on this subject at Cambridge, but whether right or quite wrong I do not know.— “In every wave does not the upward impulse of the particles, lessen the lateral pressure both behind and in advance; and in consequence as the undulation travels onward, must not the fluid in advance fall below the general level by as much as, the summit of the wave rises above it?”

I have one other question; I have reason to believe that the superficial parts of solid rock are more fractured than any other part, during an earthquake.— When a solid mass is made to vibrate, is there any particular tendency to fracture, on the surface, where the vibrations pass from the solid mass to the surrounding air, or water?— I though you would allow me to ask you these questions on paper, as you are generally so busy at the Council.—¹

I received your signature, for which I am much obliged,² I hope on Monday it will be handed over either to L^d. Minto³ or to the Chancellor of the Exchequer.—⁴

Believe me | Yours very truly | Chas. Darwin

36 Grt Marlborough St.— 18^th. June.—