466 Life and- Letters of Francis Galton
modulus) is formed on A'B'. Now I open the trap doors, successively; the shot in each vertical compartment rushes down and forms its own exponic hillock, and we have already seen what
the sum of them will be. The ratio of the moduli of these heaps is self-evident (they vary as the square root of the indices which vary directly as the length of passage of the shot). For
my Royal Institute lecture, I shall simply go into generalities to show what Reversion, etc., mean and how a law is possible, and shall hang up the formulae, but not speak a word about them. Affectionately yours, FRANCIS GALTON.
To GEORGE DARWIN, EsQ.
The substance of this letter appears in Galton's R. I. Lecture of Feb. 9, 1877: see Vol. 111A, pp. 6-11.
42, RUTLAND GATE, S.W. July 14, 1877.
DEAR STOKES*, With reference to our land meteorology, would you kindly consider and advise on the following point (which notwithstanding first appearances really falls within that branch). It is, what form of mechanical indication or registration would best convey "sea-disturbance"? I presume what is wanted the most is some idea of the ship-wrecking or
* Later Sir George G. Stokes.