Chapter XVI

.) for ordinary scientific observations. It has a projecting ledge, _B_, to carry off rain from the instruments, the slab, _A_, being erected vertically. The hygrometer is placed at _E_, with the vase of water at _F_. An alcohol minimum thermometer is represented at _C_, in the position most favourable to its certain action; and at _D_ is shown one of Negretti & Zambra's maximum thermometers, the position of which may be more nearly horizontal than there exhibited, although a slight depression of the bulb-end of the frame is desirable, but not necessary, as this thermometer can be used in any position.

##