under the railway bed. There is another suspension bridge across the
Niagara river at a distance of only about fifty rods from the falls,
on the American side. This is only for carriages and foot travel. It
was finished in 1869. It is 1,190 feet long from cliff to cliff, 1,268
feet from tower to tower, and 190 feet above the river, which at this
point is a little over 900 feet in width.


THE SPEED OF SOUND.--It has been ascertained that a full human voice,
speaking in the open air, calm, can be heard at a distance of 400 feet;
in an observable breeze a powerful human voice with the wind is audible
at a distance of 15,840 feet; the report of a musket, 16,000 feet; a
drum, 10,560 feet; music, a strong brass band, 15,840 feet; very heavy
cannonading, 575,000 feet, or 90 miles. In the Arctic regions
conversation has been maintained over water a distance of 6,766 feet. In
gases the velocity of sound increases with the temperature; in air this
increase is about two feet per second for each degree centigrade. The
velocity of sound in oxygen gas at zero C. is 1,040 feet; in carbonic
acid, 858 feet; in hydrogen, 4,164 feet. In 1827 Colladon and Sturm
determined experimentally the velocity of sound in fresh water; the
experiment was made in the Lake of Geneva, and it was found to be 4,174
feet per second at a temperature of 15 degrees C. The velocity of sound
in alcohol at 20 degrees C. is 4,218 feet; in ether at zero, 3,801; in
sea water at 20 degrees C., 4,768. By direct measurements, carefully
made, by observing at night the interval which elapses between the flash
and report of a cannon at a known distance, the velocity of sound has
been about 1,090 per second at the temperature of freezing water.


DESCRIPTION OF THE YELLOWSTONE PARK.--The Yellowstone National Park