Miscellaneous correspondence and some related papers on pure mathematics and other subjects. The correspondents include, among others, E. Sabine, R. Mallet, H.A.E.A. Fayé and E. Grey. The material covers investigations by A. de Morgan into series; consecutive fractions; laws of thought; the surface area of crumpled wire; a geometrical theorem; partial differential equations; the term 'probable area'; computations of the logarithm of m/n and e[Pi]and e2[Pi); squaring the circle; the movement of Saturn's rings; geocentric latitude; pendulums; Airy's walking experiment; a French paper on tachometers; earthquake wave velocity; the velocity of sound; a lunatic's explanation of cholera; computations for a wave; and F. Zantedeschi's paper on capillary action.