The indications of a barometer being dependent on the relative movements of the mercurial column, the scales here described are intended to afford a simple means for the necessary comparative observations.

Referring to the diagram, it will be seen there are the usual scales on both sides of the tube divided into inches and tenths; outside these are movable pieces - indices - arranged to be moved up or down, and be held where placed by a flat spring behind each. Across the center of the indices is a line lettered "Settled," and other lettering is as shown, which is. however, entirely arbitrary. One of these indices is labeled "For To-day," and the other "For To-night."

Fig. 169 - The scale in place.

In use the day index is set with the "settled"' line even with the top of the mercurial column at 9 o'clock in the evening; the night index being set in the same way at 9 o'clock in the morning each day. The reading of either index holds good until the time arrives for setting the other index, and then remains an indication of the general barometric tendency for the preceding twelve hours.

These indices, used as described, take the barometer somewhat out of the scientific class, and place it on a plane where it may become of everyday popular interest and utility.

It is known that rising barometer generally means improved weather conditions, while falling barometer indicates the opposite; but the direction of the wind should be considered in connection with the barometric indications; as changing barometer with a given wind may indicate simply an approaching change of temperature, while with a different wind the change would be of a general character. The changes which follow a rapid rise or fall of volume, though likely to be very marked, are not usually very lasting.

Daily observations of a barometer and the general weather conditions will be found most interesting and instructive when assisted by these handy "indices."