Errata

ERRATA. Page. Line. 72. 2. for communicated read communicated 77. 12. for mercury removed without causing this to rise read remove without causing the mercury to rise 81. 9. for smaller towards the middle read larger towards the middle 391. — the last line, for — read + 403. 12. for — 54 read — 46 408. 3. from the bottom, for $\frac{rn+m}{n}$ read $\frac{n}{rn+m}$