Scientific Intelligence. 187 
membrane, distinct, and rather thicker than natural. 'The retina was 
unchanged ; the solid body within was marked by the same depres- 
sion which had been observed externally. It was of a pale white 
color, and was internally of a cellular texture, like the cancelli of the 
long bones. The crystalline was indurated and of a yellowish white 
color ; the optic nerve was wasted.—Idem. 
9. Zoological Weather’ Glass. (Mag. of Nat. Hist. IV. 479.)— 
At Schwitzengen, in the post house, we witnessed for the first time, 
what we have since seen frequently, an amusing application of zoo- 
logical knowledge, for the purpose of prognosticating the weather. 
Two frogs, of the species Rana arborea, are kept in a glass jar about 
eighteen inches in height, and six inches in diameter, with the depth 
of three or four inches of water at the bottom, and a small ladder 
reaching to the top of the jar. On the approach of dry weather the 
frogs mount the ladder, but when wet weather is expected, they de- 
scend into the water. ‘These animals are of a bright green, and in 
their wild state, here climb the trees in search of insects, and make 
a peculiar singing noise before rain. In the jar they get no other 
food than now and then a fly, one of which we were assured, would 
serve a frog for a week, though it will eat from six to twelve in a day, 
if it can getthem. In catching the flies, put alive into the jars, the 
frogs display great adroitness.—Idem. . 
ARTS. 
1. Manufacture of Red Crayons, for Drawing.—Pulverize a 
certain quantity of hematite in porphyritic or other hard mortar, ming- 
ling it with filtered water, so as to reduce it to an impalpable powder. 
This is to be diluted with a sufficient quantity of water to allow the 
finest portions of the mixture to pass through a fine seive, placed 
over a vessel of water. The liquid holding the hematite in suspen- 
sion, is agitated and left in repose for twenty four hours; the water 
is then decanted cautiously, and the fine powder remains at the bot- 
tom. This is to be incorporated with gum = isinglass, in 
proportions, varying according to the use to which the crayon 1s to 
be stoked viz: 1. For — of a tender quality, which leave large 
marks, eighteen grains of dry gum arabic, to one ounce of well pre- 
pared hematite. 2. For harder crayons, destined for small delicate 
strokes, twenty two grains of gum to one ounce of powdered hematite. 
