METEOROLOGY AND CLIMATOLOGY. 
13 
mark 50° * 2, if nearly one-third of the way to the next mark 50° * 3, if 
almost half-way 50° * 4, exactly half-way 50° * 5, a little more than half¬ 
way 50° * 6, about two-thirds of the way 50° * 7, if nearly up to the next 
mark 50°*8, and if just lower than the mark of 51° it is 50 o, 9. The eye 
soon becomes accustomed to estimating these distances. 
In using a thermometer below zero, the observer must .pay attention 
to the change in the direction of reading the scale, the fractions of a 
degree counting downward from the degree mark instead of upward 
from it, as in readings above zero. Readings below 
the zero of the scale are distinguished in recording 
them by prefixing the minus sign. The annexed figure 
shows the reading of two thermometers graduated 
to fifths of a degree, one showing a temperature 
of 1°’4, the other of -l 0, 4 The importance of 
remembering that the scale is inverted at the zero 
point is of course greater in the case of a Centigrade 
thermometer, where the zero is at the freezing point 
of water. 
Care of Thermometers .—Mercurial thermometers will 
always be employed for ordinary purposes in places 
where the temperature is not likely to fall to - 40°: 
i.e., everywhere except in the polar regions and the 
interior of continents north of 50° N. These thermo¬ 
meters are very strong and are not easily broken 
except by violence. The one vulnerable part is the ^ , v d' 
bulb, which is of thin glass and filled with heavy ^ 
mercury. Hence, in carrying thermometers, care has Scale above and 
to be taken to protect the bulb from coming in contact below Zero. 
with any hard object. The best way to carry an 
unmounted thermometer is in a closed brass or vulcanite tube with a 
screw top, the inside of the tube being lined with india-rubber and pro¬ 
vided with a cushion of cotton-wool for the bulb to rest on. If the 
thermometer is mounted in a wooden frame it should be secured in a 
box so that the frame is firmly held and the bulb projects into a vacant 
part of the box, which may be lightly filled with cotton-wool or provided 
with a deep and well-padded recess. Every thermometer which is not 
graduated above 120° should have an expansion at the top of the tube 
