254 Report of Chemistry and 
of small dimensions. Let them be heated 
red hot, and rubbed over in that state 
with wax. This substance will close the 
pores of the metal which the fire has di¬ 
lated, and thereby preclude the action of 
the oxigen of air upon it. For other iron 
implement machines, &c. not susceptible of 
the above process, a similar effect may be 
obtained from varnish, discovered after six 
years research, by M. Lampodius, pro¬ 
fessor of chemistry, at Freyburg in Saxony. 
This varnish is not to be heated ; it resists 
the action of humid air, and even that of 
acid vapours. It is made in the manner 
following:—Reduce an ounce of plomba- 
gine (lead and silver ore) or ambracite to 
an impalpable powder; mix with it four 
ounces of sulphate of lead and one ounce of 
sulphate of zinc ; add to this gently (or a 
little at a time) a pound of varnish pre¬ 
pared with linseed oil—heat the whole to 
boiling. This varnish will close up the 
pores, &c. very speedily. The sulphate 
of lead is prepared by putting a dissolu¬ 
tion of acetate of lead into twelve ounces 
of water, with a dissolution of seven 
ounces of sulphate of soda (Glauber’s salts) 
into fourteen ounces of water. The preci¬ 
pitate from this mixture is a sulphate of 
lead, to be filtered, edulcorated and dried. 
The Annales Maritime$ report the dis¬ 
covery of a new method to determine the 
latitude, by a single non-meridian height, 
deduced from two other heights taken in a 
very short space of time. 
The Mnemosyne , a Finland Journal, 
makes mention of a singular stone, (there¬ 
in called meteorological) in the northern 
part of the province, which serves there 
as a sort of public barometer. At the 
approach of rain it takes a black or 
greyish black colour, and w hen the wea¬ 
ther changes to fair, it becomes covered 
with white spots. It is probably an ar- 
gillous substance, containing rock salt, or 
ammoniac, or saltpetre, and absorbing 
more or less of moisture, as the atmosphere 
is more or less charged with it. In the 
latter case, the saline particles erystalis- 
ing, will become visible to the eye and 
form the white spots. 
Capt. Henry Kater, F.R.S. has pub¬ 
lished the following notice respecting a 
volcanic appearance in the moon :— £< On 
Sunday evening, the 4th February, I ob¬ 
served a luminous spot in the dark part of 
the moon, which I was inclined to ascribe 
to the eruption of a volcano. The tele¬ 
scope used was an excellent Newtonian of 
6j: inches aperture, with a power of 74. 
The moon was exactly two days old, and 
the evening so clear, that 1 was able to 
discern the general outlines in the dark 
part of her disc. Her western azimuth was 
about 70°, and her altitude about 10 de¬ 
grees. In this position at 6 hours 30 
minutes, the volcano was situated (esti- 
Experimental Philosophy. [Oct \ 7 
mating by the eye) as in the accompanying 
sketch [distant from the northern limb of 
the moon about one-tenth of her diameter.] 
Its appearance was that of a small nebula 
subtending an angle of about three or four 
seconds. Its brightness w as very variable 
a luminous point, like a small star of the 
6th or 7th magnitude, would suddenly ap¬ 
pear in its centre, and as suddenly disap¬ 
pear, and these changes would sometimes 
take place in the course of a few seconds. 
On the evening of the 5th, having an en¬ 
gagement which prevented my observing 
it myself, I arranged the telescope for two 
friends, who remarked the same phcenome- 
na as the night before, but in an inferior 
degree, partly perhaps in consequence of 
the evening not being so favourable. On 
the 6th I again observed it; it had cer¬ 
tainly become more faint, and the star-like 
appearance less frequent. I could see it 
very distinctly with a power of 40. As the 
moon approached the horizon, it was visi¬ 
ble only at intervals when the star-like ap¬ 
pearance took place. On the same evening 
I had the pleasure of showing it to Mr. 
Henry Browne, F.R.S. I regret that I had 
no micrometer adapted to my telescope; 
but I have reason to believe the distance 
of the volcano from the edge of the moon 
was about one-tenth of her diameter, and 
the angle it formed this evening with a line 
joining the cusps w r as about 50°. I remarked 
near the edge of the moon, a well-known 
dark spot, from which the volcano was 
distant, as nearly as I could estimate, 
three times its distance from the edge of the 
moon. In a map of the moon published by 
Dr. Kitchener (and which is the best small 
map with which I am acquainted,) there is 
a mountain sufficiently near the situation 
of the volcano, to authorize the supposition 
that they may be identical. On the 7th I 
could still see the volcano, and the occa¬ 
sional star-like appearance ; but I do not 
think it was sufficiently perceptible to have 
been discovered by a person ignorant of its 
precise situation. I aminclined however'to 
think, that the difficulty of seeing it is rather 
to be f attributed to the increased light of the 
moon, than to the diminished action of the 
volcano. The spot in which I observed the 
volcanic appearance is that named Aristar¬ 
chus. This spot was particularly examined 
by Hevelius, who calls it Mons Porphyrites, 
and w'ho considers it to be volcanic. If his 
drawings are to be relied upon, it has un¬ 
dergone a considerable change in its ap¬ 
pearance since his time. Sir William Hers- 
chel has recorded in his Philosophical 
Transactions an observation of three vol¬ 
canoes, which he perceived in the moon, 
April 19. 1787, at 10k 36% sidereal time. 
One of these, which he says showed “ an 
actual eruption of fire or luminous matter,” 
was distant from the northern limb of the 
moon 3' 57"* 3, the diameter of the burning 
part 
