for computing the Astronomic Refraction. 25 
These two branches of philosophy are apparently very distinct 
from each other, and separated by boundaries that do not 
at first sight appear even to approximate. It is therefore 
pleasing to discover a case wherein one of them is capable of 
affording assistance to the other; as it shows their mutual de- 
pendence, and consequently the advantages of cultivating and 
improving at the same time all the departments of human know- 
ledge. 
By consulting Dr. Thomson’s valuable Treatise of Chemistry, 
vol. i. p. 494, on the expansion of atmospheric air, we read as 
follows : 
“From the experiments of Dalton and Gay-Lussac it ap- 
pears that all gaseous bodies whatever undergo the same ex- 
pansion by the same addition of heat, supposing them placed 
under similar circumstances. Gay-Lussac found that air by be- 
ing heated from 32° to 212°, expanded from 1000 to 1375 parts 
under a pressure =0°76 of a metre (=29°92152 English inches) . 
Mr. Dalton found that 1000 parts of air, heated from 55° to 
212°, expanded to 1325 parts. He found also, that the ex- 
pansion of air is very nearly equable; or that the same increase 
of bulk takes place, by the same addition of caloric, at all dif- 
ferent temperatures. The expansion from 95° to 1334°, was 
167 parts; and from 1334 to 212 it was 108 parts. He has 
also shown that the expansion of air follows a regular geometric 
progression, if we suppose that mercury expands as the square 
of the temperature from the freezing point: and he has rendered 
it probable, that the expansion of water and mercury is as tle 
square of the temperature of each, reckoning from their respec- 
tive freezing poimts. He finds, if this law be supposed, that 
the expansion »f water and mercury corresponds: hence he in- 
fers, that all liquids follow the same law; or that they expand 
as the square of the temperature, from the freezing point of 
each.” 
If we reduce these experiments to the same standard, and 
then bring their results into one point of view, they will be as 
follows : 
First : M. Gay-Lussac found that air by being heated from 
32° to 212° expanded from 1000 parts to 1375 parts. ‘There- 
fore for 180 degrees it expanded makes of the whole: consequently 
as 180: 7: Js a = 0:002083 the expansion for each 
degree of the thermometer when taken throughout the whole 
extent of the scale from the freezing to the boiling point. 
Secondly: Mr. Dalton found that air when heated from 55° 
to 212° expanded from 1000 to 1325 parts: therefore, as 
157: 
‘ 
