THE 
fall of the thermometer, and therefore at- 
tempts have been made to make them mark 
the greatest degree of heat and cold, in the 
absence of the observer. We will notice 
one, intended to show the greatest degree 
of heat. AB, fig. 6, is a glass tube, with 
a cylindrical bulb, B, at the lower end, and 
capillary at the other, over which there is a 
fixed glass ball, C. The bulb, and pait of 
the tube, are filled with mercury, the top 
of which shows the degrees of heat. The 
upper part of the tube, above the raercniy, 
is filled with spirit of wine ; the ball, C, is 
likewise filled with the same liquor, almost 
to the top of the capillary tube. When the 
mercury rises, the spirit of wine is also 
raised into the ball, C, which is so made 
that the liquor cannot return into the tube 
when the mercury sinks ; ot course, the 
height of the spirit in the ball, added to 
that in the tube, will give the greatest de- 
gree of heat. To make a new observation, 
the instrument must be inclined till the li- 
quor in the ball cover the end of the capil- 
lary tube. 
In 1782, Mr. Six proposed another self- 
registering thermometer. It is properly a 
spirit of wine thermometer, though mercu- 
ry is also employed for supporting an in- 
dex : ab (fig. 7) is a thin tube of glass six- 
teen inches long, and five-sixteenths of an 
inch calibre; cde, and fgb, are smaller 
tubes, about one-twentieth of an inch cali- 
bre. These three tubes are filled with highly 
rectified spirit of-wine, except the space be- 
tween d andg, which is filled with mercury. 
As the spirit of wine contracts or expands 
in the middle tube, the mercury falls or 
rises in the outside tubes. An index, such 
as that represented in fig. 8, is placed on 
the surface, within each of these tubes, so 
light as to float upon it: A: is a small glass 
tube, three-fourths of an inch long, herme- 
tically sealed at each end, and inclosing a 
piece of steel wire nearly of its own length. 
At each end, I m, of this small tube, a short 
tube of black glass is fixed, of such a diar 
meter as to pass freely up and down within 
either of the outside tubes of the thermo- 
meter, c e, or fh. From the upper end of 
the index is drawn a spring of glass to the 
fineness of a hair, and about five-sevenths 
of an inch long ; which, being placed a lit- 
tle oblique, presses lightly against the inner 
surface of the tube, and prevents the index 
from descending when the mercury de- 
scends. These indexes being inserted one 
into each of the outside tubes, it is easy to 
jiuderstand how tliey point out the greatest 
THE 
heat or cold that has happened in the ob- 
server’s absence. When the spirit of wine 
in the middle tube expands, it presses down 
the mercury in the tube, hf, and conse- 
quently raises it in the tube, eo j conse- 
quently, the index on the left hand tube is 
left behind, and marks the greatest cold, 
and the index in the right hand tube rises, 
and marks the greatest heat. 
The common contrivance for a self-regis- 
tering thermometer, now sold in most of 
the London shops, consists simply of two 
thermometers, one mercurial, and the other 
of alcohol, (fig. 9) having their stems hori- 
zontal ; the former has for its index a small 
bit of magnetical steel wire, and the latter 
a minute thread of glass, having its two ends 
formed into small knobs, by fusion in the 
flame of a candle. 
The magnetical bit of wire lies in the va- 
cant space of the mercurial thermometer, 
and is pushed forward by the mercury 
whenever the temperature rises, and pushes 
that fluid against it ; but when the tempe- 
rature falls, and the fluid retires, this index 
is left behind, and consequently shows the 
maximum. The other index, or bit of glass, 
lies in the tube of the spirit thermometer 
immersed in the alcohol : and when the spi- 
rit retires, by depression of temperature, 
the index is carried along wdth it, in appa- 
rent contact with its interior surface ; but, 
on increase of temperature, the spirit goes 
forward and leaves the index, which there- 
fore shows the minimum of temperature 
since it was set. As these indexes merely 
lie in the tubes, their resistance to motion 
is altogether inconsiderable. The steel in- 
dex is brought to the mercuiy by applying 
a magnet on the outside of the tube, and the 
other is duly placed at the end of the co- 
lumn of alcohol, by inclining the whole in- 
strument. 
THERMOSCOPE, an instrument show- 
ing the changes happening in the air with 
respect to heat and cold. The word ther- 
moscope is generally nsed indifferently with 
that of thermometer, though there is some 
difference in the literal import of the two ; 
tlie first signifying an instrument that shows, 
or exhibits, the changes of heat, &c. to the 
eye ; and the latter, an instrument that 
measures those changes ; on which founda- 
tion the thermometer should be a more ac- 
curate thermoscope, &c. 
THESIS, a general position which a per- 
son advances, and offers to maintain. In 
colleges it is frequent to have placards, con- 
