Another of these caves is near the North Mountain, in the county of Frederick, on the lands of Mr. Zane. The entrance into this is on the top of an extensive ridge. You descend 30 or 40 feet, as into a well, from whence the cave then extends, nearly horizontally, 400 feet into the earth, preserving a breadth of from 20 to 50 feet, and a height of from 5 to 12 feet. After entering this cave a few feet, the mercury, which in the open air was at 50°, rose to 57° of Farenheit's thermometer, answering to 11° of Reaumur's, and it continued at that to the remotest parts of the cave. The uniform temperature of the cellars of the observatory of Paris, which are 90 feet deep, and of all subterranean cavities of any depth, where no chymical agents may be supposed to produce a factitious heat, has been found to be 10° of Reaumur, equal to 54½° of Farenheit. The temperature of the cave above mentioned so nearly corresponds with this, that the difference may be ascribed to a difference of instruments.
At the Panther Gap, in the ridge which divides the waters of the Cow and the Calf Pasture, is what is called the Blowing Cave. It is in the side of a hill, is of about 100 feet diameter, and emits constantly a current of air of such force, as to keep the weeds prostrate to the distance of 20 yards before it. This current is strongest in dry frosty weather, and in long spells of rain weakest. Regular inspirations and expirations of air, by caverns and fissures, have been probably enough accounted for, by supposing them combined with intermitting fountains; as they must of course inhale air while their reserviors are emptying themselves, and again emit it while they are filling. But a constant issue of air, only varying in its force as the weather is dryer or damper, will require a new hypothesis.[1] There is another Blowing Cave in the Cumberland Mountain, about a mile from where it crosses the Carolina line. All we know of this is, that it is not constant, and that a fountain of water issues from it.
The Natural Bridge, the most sublime of Nature's works, though not comprehended under the present head, must not be
- ↑ See Musschenbroek, § 2,604.
