Erratum

ADDITIONS AND CORRECTIONS. Page 135, last line but two, for $\sigma \frac{dx}{dt}$, read $\sigma \frac{dx_o}{dt}$ one, for $\sigma \frac{dy}{dt}$, read $\sigma \frac{dy_o}{dt}$ , for $\sigma \frac{dz}{dt}$, read $\sigma \frac{dz_o}{dt}$ 141, line 1, for $\sigma' \rho^o \cos \lambda^o \sin (c^o - n)$, read $\sigma' \rho^o \cos \lambda^o \sin (c^o - n)$ 151, — 1, for $\frac{(r^2 - r'^2)^2}{(r + r')^2}$, read $\frac{(r^2 - r'^2)^2}{(r + r')^2}$ 180, — 9, for $\sigma' \rho^o \cos \lambda^o \sin (c^o - n)$, read $\sigma' \rho^o \cos \lambda^o \sin (c^o - n)$ 399, line 11, for perfectly, read perfectly flat 18, for S, read S' 22, for s, read s', and for rs, read rs' 402, table, col. 3, for $4^\circ 37'$, read $3^\circ 37'$ 403, line 12, for Ms'Nt, read Ms'Nt' 487, — 3, at the word iodine, add the following note: I am obliged to M. Courtois for the iodine employed in these experiments, who, with great liberality, furnished me with a considerable quantity.