xiv Historical Sketch of the Physical Sciences, 1818. 
lass. Every kind of glass tried was found to dilate the same. 
The dilatation of iron, copper, and platinum, was determined by 
fixing rods of these metals of known weights in the centre of a 
glass tube, shut at one end, and filled with mercury. The tube 
was then heated to different temperatures, and the expansion of 
the mercury ascertained by the quantity of it driven out of the 
tube. It is obvious that the volume of mercury driven out is 
equal to the dilatations of the mercury and the metal, minus the 
dilatation of the glass. The following table exhibits the absolute. 
dilatations of these bodies. 
Absolute dilatation of 
Temperature 
centigrade. Glass. Iron, Copper. Platinom. 
= aes —__—_—— owe | eee _ 
100 wise LEXA TIS aris 
200 at | 
300 | STE za7 OU tos. |. eva. 
2. Dilatation of Steam and other Vapours.—Last year has 
produced a valuable set of experiments upon the expansion of 
steam and the vapours of sulphuric ether, alcohol, naphtha, and 
oil of turpentine, when exposed to various temperatures. These 
experiments were made by Dr. Ure, of Glasgow, and have been 
published in the Philosophical Transactions for 1818. This 
subject had already attracted the attention of Gay-Lussac and 
of Dalton. But these philosophers did not carry their experi- 
ments beyond the boiling point of water. Dr. Ure’s experiments 
were contrived with considerable ingenuity ; and if they were 
oa peat with the requisite attention to precision, were calcu- 
ated to yield results sufficiently aceurate. His method was to 
vonfine a given bulk of vapour in the shut end of an inverted glass 
syphon of the requisite length. This end was surrounded by oil 
which was raised to the requisite temperature by means of an 
Argand lamp. Then mercury was poured into the open end of 
the syphon till the bulk of the vapour was reduced to its initial 
bulk. The height of mercury in the tube gave directly the elas- 
ticity of the vapour at the temperature observed. The great 
difficulty in experiments of this nature is to lute the vessel con- 
taining the oil round the glass syphon so as to prevent the oil 
from leaking out. There is also considerable difficulty in keep- 
ing the oil at a fixed temperature till the requisite quantity of 
mercury be poured into the tube, I instituted a set of experi- 
ments in somewhat a similar manner; but with a different object 
in view, a good many years ago. 1 found that tolerably accurate 
results were obtained when three persons were employed at once 
namely, one person to regulate the temperature of the oil, and to 
ascertain the bulk of the vapour; one person to pour in the 
mercury into the open ed of the syphon; and one person to 
