Note 112 — ON SOME PHENOMENA ATTENDING THE FLIGHT OF PROJECTILES.[110]

The German phrase is Schlierenmethode, by which term the method is known even by American physicists. It is also called in English the "shadow-method." But a term is necessary which will cover all the derivatives, and so we have employed alternatively the words striate and differential. The etymology of schlieren, it would seem, is uncertain. Its present use is derived from its technological signification in glass-manufacturing, where by die Schlieren are meant the wavy streaks and imperfections in glass. Hence its application to the method for detecting small optical differences and faults generally. Professor Crew of Evanston suggests to the translator that schlieren may be related to our slur (L. G., slüren, to trail, to draggle), a conjecture which is doubtless correct and agrees both with the meaning of schlieren as given in the large German dictionaries and with the intransitive use of our own verb slur, the faults in question being conceived as "trailings," "streakings," etc.—Trans.