Classes.  There are about as many twins in the births of thought as of children.  For the first time in your lives you learn some fact or come across some idea.  Within an hour, a day, a week, that same fact or idea strikes you from another quarter.  It seems as if it had passed into space and bounded back upon you as an echo from the blank wall that shuts in the world of thought.  Yet no possible connection exists between the two channels by which the thought or the fact arrived.  Let me give an infinitesimal illustration.

One of the Boys mentioned, the other evening, in the course of a very pleasant poem he read us, a little trick of the Commons-table boarders, which I, nourished at the parental board, had never heard of.  Young fellows being always hungry—­Allow me to stop dead-short, in order to utter an aphorism which has been forming itself in one of the blank interior spaces of my intelligence, like a crystal in the cavity of a geode.

Aphorism by the Professor.

In order to know whether a human being is young or old, offer it food of different kinds at short intervals.  If young, it will eat anything at any hour of the day or night.  If old, it observes stated periods, and you might as well attempt to regulate the time of highwater to suit a fishing-party as to change these periods.  The crucial experiment is this.  Offer a bulky and boggy bun to the suspected individual just ten minutes before dinner.  If this is eagerly accepted and devoured, the fact of youth is established.  If the subject of the question starts back and expresses surprise and incredulity, as if you could not possibly be in earnest, the fact of maturity is no less clear.

—­Excuse me,—­I return to my story of the Commons-table.—­Young fellows being always hungry, and tea and dry toast being the meagre fare of the evening meal, it was a trick of some of the Boys to impale a slice of meat upon a fork, at dinner-time, and stick the fork holding it beneath the table, so that they could get it at tea-time.  The dragons that guarded this table of the Hesperides found out the trick at last, and kept a sharp look-out for missing forks;—­they knew where to find one, if it was not in its place.—­Now the odd thing was, that, after waiting so many years to hear of this college trick, I should hear it mentioned a second time within the same twenty-four hours by a college youth of the present generation.  Strange, but true.  And so it has happened to me and to every person, often and often, to be hit in rapid succession by these twinned facts or thoughts, as if they were linked like chain-shot.