lossary Of The Principal Scientific Terms Used In The Present Volume

(I am indebted to the kindness of Mr. W.S. Dallas for this Glossary, which has been given because several readers have complained to me that some of the terms used were unintelligible to them.

Mr. Dallas has endeavoured to give the explanations of the terms in as popular a form as possible.)

ABERRANT. — Forms or groups of animals or plants which deviate in important characters from their nearest allies, so as not to be easily included in the same group with them, are said to be aberrant.

ABERRATION (in Optics). — In the refraction of light by a convex lens the rays passing through different parts of the lens are brought to a focus at slightly different distances —