Page:The American Cyclopædia (1879) Volume VII.djvu/307

 FLYING SQUIRREL FOG 299 Pallas) is about 10 in. long, of which one half is the tail ; the color above is light yellowish brown, the tail being rather smoke-colored, and white beneath ; the fur, as in all the spe- cies, is very soft and fine. It is a nocturnal animal, rarely appearing until sunset, at which time its gambols and graceful flights may be often seen in places frequented by it ; the large eyes indicate its habits, which make it rather an uninteresting pet, as it is lively only at night ; it is harmless and gentle, and soon be- comes tame, eating the usual food of squirrels. There is nothing resembling the act of flying in its movements, as we see in the flying fish ; it sails from a high to a lower point, a distance of 40 or 50 yards, and when it wishes to alight the impetus of its course enables it to ascend in a curved line to about one third of the height from which it descended ; running quickly to the top of the tree, it redescends in a similar manner, and will thus travel a quarter of a mile in the woods in a few min- Flying Squirrel (Sciuropterus Hudsonius). utes without touching the earth. Flying squir- rels are gregarious, six or seven being found in a nest, and considerable numbers in the same hollow or artificial cavity, associating with bats and other nocturnal animals ; the food consists of nuts and seeds, buds, and even meat and young birds. They produce from three to six young at a time, and have two litters in the southern states, in May and September. This species extends from tipper Canada and northern New York to the extreme southern limits of the United States, east of the Missis- sippi. The northern flying squirrel (P. or S. Hudsonius, Gmel.), found from Maine to Min- nesota and to the north, is considerably larger ; the length of the head and body is 8 in. and the tail 5 ; the color above is yellowish brown, mixed with cinereous, the hair lead-colored at the root, beneath white. It is common in Lower Canada; in the Lake Superior copper region, in the new and remote mining loca- tions, where rats and mice have not yet pene- trated, this species lives familiarly in the waljs of the log cabins, coming out at night in quest of food, and sometimes committing sad havoc among the miner's scanty stores. Other Ameri- can species are the P. or 8. alpinus (Rich.), from the Rocky mountains, resembling the last, but a little larger, and the membrane having a straight border; and the P. or 3. Oregonensis (Bach.), in Oregon and California, about the size of the northern species, with' a very broad membrane. The European species (P. or 8. volans, Linn.), found in Siberia, Po- land, and Russia proper, is a little larger than the 8. volucella, whitish gray or cinereous above, and white below ; it lives wholly on trees, eating the tender shoots of resinous and other trees. The species of pteromys inhabit- ing India and its archipelago attain a larger size than any of the preceding. The taguan (P. petaurista, Pall.) is as large as a half-grown cat; the male is bright chestnut above, and red beneath ; the female brown above, whitish below. There are several species in Java, of which the best known are the P. genibarlis (Horsf.) and P. sagitta (Perm.). The former is remarkable for the radiated disposition of long slender bristles on the sides of the head ; though living in a hot climate, the fur is thick and downy ; the general color is gray above, with a tawny tint on the back, and white be- neath ; it is about as large as the common red squirrel. The second species, like the first, is rare, and lives principally on fruits ; the color is brown above and white below. Several other species are described. FOERSTER, Wilhelm, a German astronomer, born at Griinberg, Silesia, Dec. 16, 1832. He studied in Berlin and in Bonn, where he graduated in 1854. He became second assis- tant at the Berlin observatory in 1855, first as- sistant in 1860, professor in 1863, and direc- tor of the observatory in March, 1865. He is prominently connected with the most impor- tant astronomical periodicals, and secretary of the astronomical society, and since the close of 1868 has been at the head of the commission for establishing German weights and measures upon a metrical basis. FOETUS. See EMBKYOLOGY. FOG, a body of aqueous vapor in the atmos- phere, like the clouds seen in the sky above, but distinguished from them both by its posi- tion and by the manner of its formation. A large class of clouds result from the diminu- tion of temperature produced by the elevation and expansion of moist air, and a small class is due rather to the cooling of the air by radiation in a horizontal direction to bodies of cooler air ; while again a very important class arise from the radiation of heat verti- cally into the cold interstellar regions. To these simple causes also must be attributed the formation of a large class of fogs. On the other hand, the peculiar feature in the origin of a number, and especially of the heaviest