year. References: Bulletins of the Department of Agriculture and of the State Experiment Stations.
Blind Fishes. The caves of the United States are inhabited by six species of fish with imperfect eyes. Five of them have rudimentary eyes, and in one the eyes are very degenerate. They belong to the family Amblyopsidæ. They are small fishes related to minnows. Their senses of hearing and touch are highly developed and enable them to capture prey. The formation of these blind animals is an interesting problem. They respond negatively to the stimulation of light, and doubtless they sought the caves voluntarily instead of being carried in by accident. There are also blind fishes in the depths of the ocean and in dark places along the shores. See Eigenmann in the Pop. Science Monthly, vols. LVI and LVII, 1900.
Block and Tackle, a combination of
fixed and movable pulleys, employed to
BLOCK AND TACKLE
secure what
engineers call a large
“mechanical advantage.”
There are
various forms, of
which that
represented in the figure
will serve as a type.
Here one rope
passes over each
of the pulleys. And
since each movable
pulley gives a
mechanical advantage
of two, it is evident
that with the block
and tackle shown
in the figure one is
able to exert a force
nearly six times as
great as without its
aid. If no energy
were used up inside
the mechanism, one
could lift exactly
six times as much
with as without the
tackle. It should
be carefully observed that one secures no
gain in energy by this device. The energy
stored up in a lifted mass is always a
little less than the energy required to lift
it, whether a block and tackle be used or
not.
Block System, a system of signals at intervals along a line of railroad, intended to decrease the danger of accident. The system of telegraphing the arrival of a train from station to station, used in England as early as 1839, may be quoted as its origin. It was first introduced into the U. S. in 1876 by the Pennsylvania railroad. In general the block system divides a line into sections, upon each of which only one train is admitted at a time. The system of giving staffs, a staff being given to a train by a station-master only when one has been returned by the train previously upon that section, is a variety of block system which is adapted only to single lines. The serious accidents which occur upon American railroads have led to an agitation for the compulsory use of the block system, which is universal in England but not in America. To keep the sections clear for any one train it adds the additional safeguard of an interval of space to the universal practice of an interval of time between trains. The expense of the block system is sometimes lessened by automatic devices for block signals which minimize the direct manipulation of levers by signalmen.
Blockade, in naval warfare is the shutting up of a port of a country, cutting off communication with the outside world. It is effected by stationing sufficient numbers of ships off the ports to make entrance impracticable. Neutral powers, because the interference with their commerce injures them, must be fully notified of the blockade by the state that attempts it. Then endeavors to deal with the ports blockaded become contrary to the law of nations, and attempts to trade with such ports render ships and cargoes liable to confiscation. But if blockades are to be binding on neutrals, they must not merely be blockades on paper or blockades by proclamation. They must also be physically effective. Among famous blockades are that of the European coast from Denmark to Italy in 1807-8, when Napoleon was fighting England; the Crimea in 1854-6 by England, France and Sardinia; the coast of the Confederate States by the Federal Government during 1861-5; Cuba by America in 1898; and Venezuela by Britain, Germany and Italy in 1903.
Bloemfontein (blo͝om′fŏn-tĭn′), capital of the late Orange Free State (now the Orange River Colony), in South Africa. Here, before the outbreak of the Boer War of 1899-1901, was held the conference between President Kruger of the late Transvaal Republic, and the British High Commissioner of South Africa, Sir Alfred (now Lord) Milner. The conference met May 30, but separated June 5, 1899, without having come to any agreement. The State joined the burgher republic of the Transvaal in the war with Britain, and the capital (Bloemfontein) was entered and occupied by the British under Lord Roberts, March 13, 1900. The population is 33,900, of which more than 15,000 are whites and the rest natives.
Blood, the circulating fluid of animals. It is a nutrient fluid of varied composition. In the course of its circulation it is continually giving nourishment to the tissues
