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Rh of socialism as a difference of method: but it will be seen that this difference of method arises from ,a far more fundamental divergence in outlook and philosophy. The methods of the communists are not comprehensible save in relation to the whole philosophy of The Communist Manifesto.

Communist Organization. From the above considerations certain conclusions follow as to the role and character of the communist party in any country. The fully organized com- munist party, it is stated, is to be the " advance guard " of the working class, never regarding itself as separate from the working class, always working in and through existing working-class organizations on the plane of the struggle of the moment, but always coordinating and giving conscious direction to the differ- ent aspects of the working-class struggle with a view to the larger ultimate issue. For this purpose it must be based on the strictest internal discipline, and on severe conditions of membership; but this internal strictness of theory and discipline must be ac- companied by an external policy of revolutionary opportunism which is in contrast with the usual " purism " of the revolution- ary sect. This is the explanation of the alternate charges of " doctrinairism " and " opportunism " which are levelled by other socialists against the communist party. This discipline is ultimately international in character, because the struggle is regarded as international. To the communist the International is more than a coming-together of sympathetic parties in a common struggle: it is the union of different divisions in a single army, each with its own tactical problems, but all with a single ultimate directing centre. For this reason an absolute ultimate authority is vested in the International Executive, subject to the World Congress. This authority of the International is regarded as of particular importance, not only for the immediate struggle, but as the nucleus of future international authority in the World Soviet Republic.

Bibliography. The classic statements of communism are con- tained in the writings of Marx and Engels : in particular, The Com- munist Manifesto by Marx and Engels (1848); The l8th Brumaire (1852); Capital (1867); The Civil War in France (1871) and the Critique of the Gotha Programme (1875) by Marx; and The Origin of the Family, Private Property and the State (1884) by Engels. The Life and Teaching of Karl Marx by Max Beer (1918, English translation 1921), gives a valuable short summary of his theories. The controversial literature of Marxism is very extensive, and would need a special bibliography. The most important documents of modern communism are the writings of Lenin, especially The Stale and Revolution (1917) and Left Comtmmism, an Infantile Dis- order (1920) ; the writings of Trotsky, including The Russian Revolution to Brest Litovsk (1918); Bukharin's Programme of the World Revolution (1920), and other writings of the Russian leaders; and the publications of the Communist International, including the Congress Manifestoes (1919 and 1920), the Theses and Statutes of the Communist International (1920) and the monthly organ The Communist International. Presentations by English workers of communist theories may be found in R. W. Postgate, The Bolshevik Theory (1920) and E. and C. Paul, Creative Revolution (1920). For criticisms of communist theories see Karl Kautsky, The Dictatorship of the Proletariat (1919) ; J. R. Macdonald, Parliament and Revolu- tion (1919), and Bertrand Russell, The Practice and Theory of Bolshevism (1920). (R. P. D.)

COMPASS (see 6.804). In view of the large extension of the field covered by the term " compass " due to the introduction of the " Gyro Compass " and its adoption for navigational pur- poses, it is essential to define exactly what is meant by a word which is being very loosely applied to instruments of no practical navigational value.

The compass is an instrument designed to seek a certain definite direction in azimuth and to hold this direction perma- nently. For use in navigation, a compass must satisfy the follow- ing practical requirements:

Magnetic. When disturbed should return to within 1 of the above direction within 2 minutes of time.

Gyroscopic. When disturbed or started should return to within 1 of the above direction within 3 hours.

Magnetic Compass. The description given in the earlier article may be taken as generally applicable to the magnetic compass of the present day; a very great extension, however, in the use of the "liquid " type for nautical purposes has since taken place, while for aeronautical use the liquid compass is essential. The

British Admiralty compass department now occupies the " Compass Observatory " at Langley, Bucks., and deals with compasses of all types both for the Admiralty and Air Ministry. A comprehensive museum is now attached to the observatory. Gyro Compass. The gyro compass is an instrument in which use is made of the rotation of the earth and the properties of a rapidly spinning body to indicate some fixed direction relatively to the earth. Up to the present the only successful models have been definitely North-seeking, and all such compasses consist essentially of:

1. A wheel mounted so as to be capable of spinning rapidly with- out vibration about its axis and also free to point that axis in any direction.

2. A gravity control of some description which restricts the tilting freedom of the axis of the wheel.

Modern gyro compasses differ somewhat in the mechanical devices by which the degrees of freedom of the axis are obtained and in the methods adopted to provide the gravity control; but they are all the practical outcome of experiments made in 1852 by Foucault to demonstrate the rotation of the earth by means of a gyroscope. Edward Sang, of Edinburgh, had described in 1836 how this could be done, but he did not actually carry out the experiment. Much later, in 1884, Lord Kelvin exhibited a model gyro compass before the British Association. Early in the present century the development of submarines called for a non-magnetic type of compass, and fortunately the advance in electrical and mechanical science made it possible for Dr. Anschutz to utilize this pioneer work and evolve the first prac- tical gyro compass. In this instrument a single gyro was used and both the tilting and the azimuthal freedoms were obtained by attaching to the gyro case a float supported in a bath of mercury. A full account of this compass and the elementary mathematical theory of it is to be found in Crabtree's Spinning Tops and Gyroscopic Motion. The chief objection to this com- pass was its failure to function correctly if the ship was rolling, especially when on a quadrantal course. This intercardinal rolling error was, for some time, a stumbling-block to further progress, but in modern gyro compasses it is almost non-existent.

Anschutz in 1912 brought out a very different instrument which was adopted by the German navy. In this model three gyros are used in place of the single one of the earlier model, the two extra gyros having been introduced to overcome the rolling error.

About the same time, the Sperry Co. of New York put on the market their gyro compass. The first model was found, on trial, to be subject to rolling error and this necessitated an alteration in design, a small gyro-pendulum, called the floating ballistic, being introduced. This compass, in its modified form, was very largely used by the British and Allied navies during the war.

More recent types are the Brown, Carrie and Twin Sperry. The first is an entirely British-made compass and has many novel features; in particular, the device used to obtain the azi- muthal freedom and the gravity control. It is small and light, the whole as fitted in the binnacle weighing about 15 pounds.

Certain very important modifications of the Sperry compass were developed by the Admiralty compass department as a result of war experience, especially the mercury control attach- ment invented by Commander G. B. Harrison, O.B.E., and Mr. A. L. Rawlings; this simplifies the construction of the com- pass, reduces its cost and makes it more efficient, particularly in bad weather (fig. 4).

The most important constants of the Anschutz, Brown and Sperry wheels are as follows:

Radius of Rate of Mass Gyration Spin in in Ib. in inches. r. p. m.

Anschutz ..... 6 1-85 20,000

Brown. . : . ... 4i 1-57 15,000

Sperry 50 4-62 8,600

Precession.- So far as gyro-compass work is concerned the phenomenon of precession may be described in the following manner. If a torque is applied to a free gyro in any plane passing through the gyro-axis then the axis will precess in a plane perpendicular to the plane of the torque and also to the plane of the