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COMPRESSION

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Originally appearing in Volume V06, Page 813 of the 1911 Encyclopedia Britannica.
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COMPRESSION , in See also:

astronomy, the deviation of a heavenly See also:body from the spherical See also:form, called also the " See also:ellipticity." It is numerically expressed by the ratio of the See also:differences of the axes to the See also:major See also:axis of the See also:spheroid. The compression or " flattening " of the See also:earth is about 1/298, which means that the ratio of the See also:equatorial to the polar axis is 298:297 (see EARTH, FIGURE OF THE). In See also:engineering the See also:term is applied to the arrangement by which the exhaust See also:valve of a See also:steam-See also:engine is made to See also:close, shutting a portion of the exhaust steam in the See also:cylinder, before the stroke of the See also:piston is quite See also:complete. This steam being compressed as the stroke is completed, a See also:cushion is formed against which the piston does See also:work while its velocity is being rapidly reduced, and thus the stresses in the mechanism due to the inertia of the reciprocating parts are lessened. This compression, moreover, obviates the See also:shock which would otherwise be caused by the See also:admission of the fresh steam for the return stroke. In See also:internal See also:combustion engines it is a necessary See also:condition of See also:economy to compress the explosive mixture before it is ignited: in the See also:Otto See also:cycle, for instance, the second stroke of the piston effects the compression of the See also:charge which has been See also:drawn into the cylinder by the first forward stroke.

End of Article: COMPRESSION

Additional information and Comments

Compression can also relate to data. The compression of data relates to the removal of redundencies in the binary representation of a set of information. Common compression algorithms include Jpeg, Mpeg and MP3. MP3 is considered more as the subtraction of irrelevent data as opposed to true compression. This would give us two definitions of compression. 1) A compression where a set of data could be transformed into a smaller (cardinally-speaking) set where it is possible to re-instate the data to its original form, and 2) A compression where irrelevant information is subtracted but it would not be possible to re-instate the original set but where no measureable loss of information is percieved. Perfect compression of data would be the compression of data into the minimum possible transmittable bit set, that can be reconstituted into its original form. Perfect compression has so far eluded mankind. Although this is not a mathematically proven fact, it is widely accepted that perfect compression is not possible. Perfect compression is equivalent to perfect secrecy, the only model of perfect secrecy that exists today is the VERNAM cipher, which is not perfect compression.
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