on some of the leading Doctrines of Caloric, &c. 183 
' mencement ; then, after receiving one increment of caloric, it 
will be become 1000—1=999. Since the next unit of that. di- 
vellent agent will have to combat only this diminished cohesive 
force, it ‘will produce an effect greater than the first, in the 
proportion of 1000 to 999; and so on in continued progression. 
That the increasing ratio is, however, greatly less than Mr. Dal- 
ton maintains, may, | think, be clearly demonstrated. 
According to his table of equal increments of temperature, 
vol. i. p. 14, New System, we have the following intervals, cor- 
responding to the five successive intervals of 90° on our scale. 
From 32° to 122°, to 212°, to 302°, to 392°, to 482°. 
Intervals by Fahr. of 96°, 90", 90°, 90°, 90°. 
True intervals by Dalton, 1029-4 77°96 63°°9 55°%7 50°5 
The relative inequality of these intervals is deduced, from 
Mr, Dalton’s law, that “all pure homegeneous liquids, as water 
and mercury, expand from the point of their congelation, or 
greatest density, a quantity always as the square of the tempera- 
ture from that point.” He regards the law as resulting from the 
constitution of liquids, and therefore not applicable to solid 
bodies. This is indeed implied in its enunciation. In p. 43, 
after assigning reasons, he states, ‘ that for all practical purposes 
we may adopt the notion of the equable expansion of solids.” 
Now J am prepared to prove, either, that the expansion of 
solids partakes of the above inequability of liquids, which nobody 
imagines, and for which no reason, even hypothetical, can be 
assigned ; or, which is the only alternative, that homogeneous 
solids, and mercury, proceed almost exactly, pari passw, in their 
rates of expansion by heat. 
The experiments which justify this assertion were made by me 
about five years ago, and were then exhibited to many of my 
chemical friends, as also in my public lectures; but a wish to 
render the series more complete, has induced me to withhold 
them from the public eye, till requisite leisure could be afforded 
for this purpose. They were performed with a pyrometer of 
peculiar construction, in an oblong trough filled with melting 
ice: a strong bar of Swedish iron was placed, from which pro- 
jected at right angles four inflexible iron arms, attachable by 
powerful screws to any part of the bar. The arms nearest the 
extremities of the bar carried each a fine micrometer micro- 
scope, made by that admirable artist Mr. Troughton. ‘The other 
two arms were incurvated downwards at their extremities, which 
supported a metallic or other rod. This was fixed by two 
pinching screws at one end, but lay loose on a friction roller at 
the other. The loose end bore an elevated index. ‘The curvature 
‘of these two arms was such as to allow their extremities, with 
the attached rod, to be plunged beneath the surface of oil or 2 
avout 
