The bulb is almost wholly filled with alcohol, which acts as the principal thermometric fluid and has the advantages of a high coefficient of expansion. The thermometer bulb and the stem of the thermometer up to a point convenient for graduation, are filled with mercury. In the drawing the mercury is represented by the heavy black marking in and just above the small bulb. The peculiar construction at this point is for the purpose of retaining the mercury about the point of the slender capillary stem inside the bulb and preventing the entrance of alcohol into the stem when the thermometer is horizontal. In order to register the maximum and minimum temperatures a short column of alcohol is placed in the upper portion of the stem, above the mercury, and within this are arranged two small steel indexes, so constructed that they will not slide in the tube of their own weight, but are easily pushed upward by the mercury column or pulled downward by the top meniscus of the alcohol column. The indexes are set by means of a small magnet, the one being drawn down upon the top of the mercurial column and the other raised up against the meniscus of the alcohol column. The rise of the mercury carries its index upward, leaving it to register the highest point reached, while the alcohol meniscus withdraws the other index and leaves it at a point representing the minimum temperature. It remains only to mention that the graduations are fixed in the usual way, having reference only to the positions of the mercurial column. Beyond the highest point supposed to be reached by the mercury, say about 120°, the graduations are extended in an arbitrary manner. The scale numbers represent temperatures by the mercurial column and are continued in regular sequence beyond the 120°. On this plan the readings for minimum temperatures are on a purely arbitrary scale and are converted into true degrees of temperature by use of a table prepared for each thermometer, which table embodies as well all the corrections for instrumental error. The arrangement of the alcohol columns above the mercurial column and the indexes are shown enlarged at one side of the illustration. The readings of the maximum temperature are made from the bottom end of the index next to the mercurial column. The minimum temperature is the reading of the top of the uppermost index. Thus in the figure the maximum temperature indicated is 76.5°, and the minimum 125.7°, which, by reference to the table of correction for this thermometer, No. 10, is found to be 53.3°.