Maximum and minimum thermometers are used to record the daily maximum
and minimum temperatures. Fig. 46 shows a typical maximum and minimum
thermometer used for giving the extremes of temperature. One side of the
thermometer has a scale reading, beginning at the top, from 60° below
zero to 140° above zero. This is the scale used when determining the
coldest temperature reached during a day. The other side of the
thermometer has a scale marked from 70° below zero, beginning at the
bottom and reading up, to 130° above zero. On this side the maximum heat
reached during the day is recorded. There is a small metal piece in the
tubes, one on each side, and as the mercury pushes ahead or recedes, the
small index is left at the lowest point reached in one tube and at the
highest point reached in the other. The small metal piece is drawn back
to the level of the mercury by means of a small magnet.