us allowing the end of the capillary to be drawn
out. Reheat again until the liquid rises to the top of the tube, then
seal by means of the blowpipe flame. The thermometer is now finished
except for graduation; this is dealt with on page 75.

_An Alarm Thermometer._--A thermometer which will complete an electric
circuit when a certain temperature is reached may be made by sealing an
electrode in the bulb and introducing a wire into the top, which in this
case is not sealed. Naturally, this thermometer will be filled with
mercury. There is considerable difficulty in filling such a bulb without
causing it to crack.

Several elaborations of this form are made, in which electrodes are
sealed through the walls of the capillary tube, thus making it possible
to detect electrically the variation of temperature when it exceeds any
given limits.

_An Enclosed or Floating Thermometer._--The construction of this type of
thermometer is shown by _h_ and _i_, Fig 11. It is made in the following
stages:--A bulb is blown on the drawn-out end of a thin-walled tube as
shown by _h_. A small bulb is blown on the end of a capillary tube,
burst, and turned out to form a lip which will rest in the drawn-out
part of the thin-walled tube but is just too large to enter the bulb.
The capillary tube is introduced and sealed in position, care being
taken to expand the joint a little. The thermometer is filled and the
top of the capillary tube closed by the use of a small blowpipe flame. A
paper scale having the necessary graduations is inserted, and the top
of the outer tube is closed as shown by _i_.

_A Maximum and Minimum Thermometer._--If a small dumb-bell-shaped rod of
glass or metal is introduced into the capillary tube of a horizontally
placed, mercury-filled thermometer in such a position that the rising
mercury column will come in contact with it, the rod will be pushed
forward. When the mercury falls again the rod will be left behind and
thus indicate the maximum temperature attained. If a similar
dumb-bell-shaped rod is introduced into an alcohol-filled thermometer
and pushed down until it is within the alcohol column, it will be drawn
down by surface tension as the column falls; but the rising column will
flow passed it without causing any displacement; thus the minimum
temperature will be recorded.

Six's combined maximum and minimum thermometer is shown by _b_, Fig. 11.
In this case both maximum and minimum records are obtained fr