had been removed from the floorings had by that time been neatly replaced, and, in the case of the lower one, covered by the carpet, the removal of which had caused so much commotion in Randolph’s room on the fatal day.  Hester Dyett would have been able to notice and bring at least one of the apertures forward in evidence, but she fainted before she had time to find out the cause of her fall, and an hour later it was, you remember, Randolph himself who bore her from the room.  But should not the aperture in the top floor have been observed by the class?  Undoubtedly, if its position was in the open space in the middle of the room.  But it was not observed, and therefore its position was not there, but in the only other place left—­behind the apparatus used in demonstration.  That then was one useful object which the apparatus—­and with it the elaborate hypocrisy of class, and speeches, and candidature—­served:  it was made to act as a curtain, a screen.  But had it no other purpose?  That question we may answer when we know its name and its nature.  And it is not beyond our powers to conjecture this with something like certainty.  For the only “machines” possible to use in illustration of simple mechanics are the screw, the wedge, the scale, the lever, the wheel-and-axle, and Atwood’s machine.  The mathematical principles which any of these exemplify would, of course, be incomprehensible to such a class, but the first five most of all, and as there would naturally be some slight pretence of trying to make the learners understand, I therefore select the last; and this selection is justified when we remember that on the shot being heard, Randolph leans for support on the “machine,” and stands in its shadow; but any of the others would be too small to throw any appreciable shadow, except one—­the wheel, and-axle—­and that one would hardly afford support to a tall man in the erect position.  The Atwood’s machine is therefore forced on us; as to its construction, it is, as you are aware, composed of two upright posts, with a cross-bar fitted with pulleys and strings, and is intended to show the motion of bodies acting under a constant force—­the force of gravity, to wit.  But now consider all the really glorious uses to which those same pulleys may be turned in lowering and lifting unobserved that “ball of cotton” through the two apertures, while the other strings with the weights attached are dangling before the dull eyes of the peasants.  I need only point out that when the whole company trooped out of the room, Randolph was the last to leave it, and it is not now difficult to conjecture why.