334 On the Expansion of Elastic Fluids, 
FPostscript.—In the foregoing account of the instrument of Mr. 
Brooke, it has been assumed that the arm of the cylinder is con- 
nected directly with the hour hand of the time piece, making it 
therefore revolve once in twelve hours. The effect of this arrange- 
ment is, that when the paper is left on for twenty-four hours, we 
have two traces, which sometimes intersect in such a manner, as 
to make it difficult to distinguish to which revolution portions of 
them are due. ~The writer has recently succeeded, by a very 
simple arrangement, in making the cylinder revolve but once in 
twenty hours, and thus remedying this inconvenience. ‘T'wo 
small grooved wheels mounted on a light frame, one having a di- 
ameter exactly double that of the other, are connected by a piece 
of fine silk twist. ‘The smaller one being then connected with 
the hour hand, by a crank, and the larger one with the cylinder, 
it is evident that the object is effected. 
is reduces the time scale to six-tenths of an inch for one 
hour, which is fully equal to the scale that has been generally 
adopted in the engraved diagrams of term day and other move- 
ments, and is considered large enough for almost every purpose 
to which diagrams can be applied, while it gives great facility to 
comparisons, and a much more distinct representation of the di- 
urnal curves. 
Arr. XX XIIL.—Jnfluence of the known Laws of Motion on the 
Expansion of Elustic Fluids ; by Eur W. Buaxe. 
Tar under the controlling influence of the known laws of 
motion, elastic fluids must expand according to some definite and 
invariable law, is an obvious truth and one which has often been 
recognized by mathematicians. But the determination of that 
law isa problem which hitherto, it is believed, has not been 
solved. There are many interesting points in mechanics and 
physics, in relation to which the present state of knowledge 1s 
imperfect, which depend for their correct and complete develop- 
ment, in part at least, on a solution of this problem. It is there- 
fore a poiut of some interest to science. It is our purpose in this 
article to solve this problem ; and we shall do so by employing @ 
method similar in part to that employed in solving the problem 
of the propagation of pulses in elastic media, ii ser., vol. v, p. 37; 
of this Journal. 
