[Footnote 112: 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._] ON INSTRUCTION IN THE CLASSICS AND THE SCIENCES.[113] Perhaps the most fantastic proposition that Maupertuis,[114] the renowned president of the Berlin Academy, ever put forward for the approval of his contemporaries was that of founding a city in which, to instruct and discipline young students, only Latin should be spoken. Maupertuis's Latin city remained an idle wish. But for centuries Latin and Greek _institutions_ exist in which our children spend a goodly portion of their days, and whose atmosphere constantly surrounds them, even when without their walls. For centuries instruction in the ancient languages has been zealously cultivated. For centuries its necessity has been alternately championed and contested. More strongly than ever are authoritative voices now raised against the preponderance of instruction in the classics and in favor of an education more suited to the needs of the time, especially for a more generous treatment of mathematics and the natural sciences. In accepting your invitation to speak here on the relative educational value of the classical and the mathematico-physical sciences in colleges and high schools, I find my justification in the duty and the necessity laid upon every teacher of forming from his own experiences an opinion upon this important question, as partly also in the special circumstance that in my youth I was personally under the influence of school-life for only a short time, just previous to my entering the university, and had, therefore, ample opportunity to observe the effects of widely different methods upon my own person.