306 Natural-Philosophical Collections. 
has observed and calculated the oppositions of Saturn in 1817, 1818, 1822, 1823, 
and 1825, as well as those of Jupiter in 1818 and 1826. The object of these ob- 
servations is to perfect the astronomical tables by the comparison of the places 
calculated from observation, with the places of the planets calculated after the 
tables. The memoirs of M. Tarkhanoff furnish data worthy of attention, as 
they rectify many errors in the table with relation to the centre of the sun. Dur- 
ing a voyage round the world with the expedition commanded by Captain Was- 
silief, during the years 1819-1822, our astronomer observed at Rio Janeiro, 
five occultations of stars by the moon. For want of corresponding observations 
to render the determination of the longitude of Rio Janeiro independent of the 
errors of the lunar tables, he has chosen, with this view, the occultation of An- 
tares, as appearing to promise the most exact result, seeing that the star has 
passed almost by the centre of the moon. During the same voyage, M. Tark- 
hanoff determined the longitude of the port of Honorouro, in the island of Wa- 
gou, and corrected that of the port of Petropanlosk. 
On the action of the Solar Rays on the Nitrate of Silver, when dissolved in 
common Water; by M. Vogel.—_M. Hermbstedt was the first who attributed 
to a gaseous principle which is found in water, the property of causing the nitrate 
of silver, when in contact with it, to become red; an opinion admitted by MM. 
Kriiger, Pfaff, and other chemists. 
M. Zimmermann of Giessen, attributed the peculiarity to a vegeto-animal mat- 
ter, to which he gave the name of Pyrrhine. These different opinions led M. 
Vogel to make some experiments. He took two tubes of glass, in which he 
placed two cylinders of beech-wood, one with the bark and the cther without. In 
six months, they had become black and were covered with a gelatinous matter ; the 
liquors did not give any precipitate with the salts of iron, or with gelatine. There 
was, therefore, neither gallic acid, nor tannin ; but with the nitrate of silver they 
gave a liquid which, on being exposed to the solar rays, became red, and in some 
days lost its colour and left a deposit of a black powder. Chlorine and iodine 
entirely destroyed the colour of the solutions. All waters, in which there had 
been infnsed wood, soil, pure fibrin or blood, gave a red colour when they were 
exposed to the sun, and when nitrate of silver was added. 
_. Hence, M. Vogel thinks that Pyrrhine, to which this property has been at- 
tributed as a distinctive character, ought not to occupy a particular place amongst 
the principles of the vegetable kingdom.—Journ. de Pharmacie. 
Observations made by means of a new Telescope.—In a Boston journal it is 
related that an ingenious artist of Providence has recently constructed a telescope, 
of seven feet, on a new principle, by means of which he has been able to reflect 
upon a white screen, placed in a dark chamber, the image of the sun reduced to 
the size of a globe of eight feet in diameter. He states that his astonishment was 
exceeding when he perceived that each of the spots, to the number of nine, which 
exist at this time on the surface of the sun, was found distinctly depicted on the 
screen, to the degree that he could ascertain all their movements, considered in 
their diverse and sudden variations. He says that he could clearly perceive that 
these spots were immense volumes of smoke, which seemed to issue from many 
volcanoes ; and, as they appeared occasionally to pass out forcibly from craters, 
above which they sometimes formed thick clouds, and were sometimes dissipated, 
he considers this phenomenon as an explanation of the rapid changes which these 
spots undergo. He observes, that the emanation of so great a quantity of gas 
from the interior of the body of the sun, would preduce that brilliant and dazzling 
appearance which its atmosphere possesses. This theory may accord little with 
the opinion of other learned men who have made observations on the same subject ; 
but the author firmly relies on the solidity of his hypothesis. With the same in- 
strument, which he has constructed, he has also examined the moon, and he 
seems to be convinced that this planet is covered with snow and perpetual i ice. He- 
feels assured that the spots which are observed on its surface are iey seas, and the 
