2 Improvements in Physical Science ‘Jan. 
own bulk of each must be erroneous. Finally, M. de Saussure 
found that different liquids absorb the gases in different orders: 
thus naphtha absorbs more of olefiant gas than of nitrous oxide, 
while essential oil of lavender absorbs more of nitrous oxide than 
of olefiant gas. This can only be ascribed to the agency of che- 
mical affinity. Finally, he ascertained by experiment, that Mr. 
Dalton’s opinion respecting the quantity of gas disengaged, when 
water saturated with one gas is brought into contact with another 
gas, is inaccurate. It would appear, therefore, from these experi- 
ments of De Saussure, that Mr. Dalton’s theory is errroneous in 
every particular. 
If, HEAT. 
No new discovery respecting heat, so far as I know, has been 
made during the course of last year. Mr. Davenport, has, how- 
ever, written a very complete refutation of some objections that 
had been started against M. Prevost’s theory of radiant heat; and 
M. Prevost himself has given us a very short but clear outline of 
his theory, which has been adopted, I believe, by almost all the 
chemical philosophers of the present day. Both of these papers 
will be found in the Annals of Philosophy; the first in the fifth, 
and the second in the sixth volume of that work. M. Prevost’s 
outline of his theory being very short, it may be expected that I 
should give it here, It is in substance as follows: 
1, Heat is a discrete fluid, every particle of which moves rapidly 
ina straight line. These particles go one in one direction and 
another in another; so that every sensible point of the hot space is 
a centre from which depart, and to which arrive, rows of particles 
or calorific rays. 
2. Every calorific ray, which a body sends by emission or by 
reflection, only replaces another ray, which would take the same 
direction if the body were withdrawn. This is to be understood of 
a hot place where heat radiates. If the intercepting body is of the 
same temperature with the place, the ray which it replaces is equal 
to itself; if not, this ray or row of particles, is more or less abund- 
ant in heat. ; 
3. A reflector in a place of uniform temperature sends neither 
more nor fewer calorific rays than another body. 
4, It follows from this: 1. That in a place of uniform tempe- 
rature, a reflector of whatever form does not affect a thermometer 
subjected to its influence, 2. That if it reflect rays emanated from 
a body more or less hot than the place, it will raise or depress 
respectively the thermometer subjected to its influence. 
In the last volume of the Edinburgh Philosophical Transactions, 
published during the summer of 1815, there is a paper by Dr. 
John Murray, Lecturer on Chemistry in Edinburgh, on the Dif- 
fusion of Heat at the Earth’s Surface. This ingenious gentleman 
had started the following objection to the Huttonian theory, which 
he considered as fatal to its truth. If a central fire existed in the 
earth, as Hutton supposes, from the very nature of heat it could 
