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Webster 1913 Edition

Noun.

[

Meso-

logarithm

: cf. F.

mésologarithme

(Math.)

A logarithm of the cosine or cotangent.

[Obs.]

Kepler. Hutton.

Noun.

[Gr. middle, and logarithm.]

A logarithm of the co-sines and co-tangents.

The former is called by Napier an antilogarithm, the latter a differential.

mesologarithm ‎(plural mesologarithms)

(mathematics, obsolete) A logarithm of the cosine or cotangent.
- Johannes Kepler
  […] the antilogarithm of the greatest inclination is added to the mesologarithm of the argument, and thus the sum will be the mesologarithm of the argument of the reduction.