390 Scientific Intelligence —Mechanical Philosophy. 
perehelium would suffer only a periodical change; and that the 
nodes and the inclination of the orbit would not be altered. In the 
case of Encke’s comet, the first two effects have been decidedly 
produced, and there are two circumstances to facilitate the calcula- 
tion ; the first is, that this comet is always seen in the same point of 
its orbit, and near to its perehelium ; and the second, that its orbit is 
subjected only to very slow alterations. Both these circumstances 
permit the supposition that the times of revolution (at least for some 
periods) diminish by an equal quantity, so that their diminution may 
be considered as proportional to the square of the times ; the period- 
ical variation of the perehelium may also be neglected without incon- 
venience. M. Encke supposes, with Newton, that the ether or re- 
sisting medium, is diffused through all space; that its density dimin- 
ishes in the inverse ratio of the square of the sun’s distance, and that 
the resisting force is always proportional to the square of the actual 
— velocity of the comet.— Quar. Jour. Jul.—Sep. 1829. 
i: Breen: Active. Molecules.—Mr. Holland, the inventor of a 
presi sold by Carey of the Strand, has inclosed some of the’ 
particles described by Mr. Brown, as active molecules, between glass 
and talc, closing the whole hermetically, so as to exclude, as much 
as care could do, all interference of external causes. Notwithstand- 
ing this, the motion continued equally vivid even after ten days. The 
lens used had a focus of the thirtieth of an inch; and the particles 
were obtained, as we understand, from gamboge.—Jdem. 
3. Destruction of Vermin in ships, by steam.—By letters from In- 
dia, it appears that the application of steam has been found wonder- 
fully us in Cleansing ships from vermin, and especially the 
white ant. A steam-boat (the Comet) was placed alongside a mer- 
chant vessel, and steam from its boiler conveyed by a very simple 
system of pipes, into the hold of the latter, the apertures to which 
were closed as well as they could be. The operation was continued 
for several hours, and there is no reason to believe that it was not ef- 
fectual, and will prove a valuable process in the navy. ~ Besides the 
direct object of cleansing the ship, another advantage accrued, from 
the discovery of every leaky place existing, by the oozing of the wa- 
ter through them, in which way leaks were made manifest, that could 
: _ not be found out otherwise. ‘The expense is said to be very mode- 
=a id itis further stated to be the only process at present known, 
