s may
be found; it must show what experiments are to be performed by each
student at a given time; it must give information as to the place in the
laboratory where the apparatus is deposited; it must show to the
instructor what experiments have been performed by each student; it must
prevent the assignment of the same experiment to two students; it must
enable the instructor to assign the same experiment to two or more
students; it must form a complete record of what has been done, what
work is incomplete, and what experiments have not yet been assigned; it
must also be so arranged that new experiments or sets of experiments may
be exhibited.

+------+---+---+---+---+---+---+---+---+
| | A | B | C | D | E | F | G | H |
+------+---+---+---+---+---+---+---+---+
| 1 | * o o * o o o o |
| 2 | * o * * o o o o |
| 3 | + * * * o o o o |
| 4 | + o * * o o o o |
| 5 | o + * * * * o o |
| 6 | o + * * o * o o |
| 7 | o o + * o o o o |
| 8 | o o o + * o o o |
| 9 | o o o * + o o o |
| 10 | o o o o o + o o |
| 11 | o o o * o o + * |
| 12 | o o * * o + + + |
| 13 | o o * o o o o o |
| 14 | o o * o o o o o |
| 15 | o o + o o o o o |
| 16 | o o + + * o o * |
+--------------------------------------+

A, B, C, etc., are cards upon which are the names of students. 1,
2, 3, etc., are cards like the one described in the article. The
small circles (o) represent unassigned experiments. The black
circles (*) (slate nails) represent work done. The caudate circles
(+) (brass nail) represent work assigned.

The indicator consists of a plank of any convenient length and breadth.
The front surface is divided into squares of such size that the pegs may
be introduced and withdrawn with ease. At each corner of the squares
holes are bored into which nails may be placed. There is a blank border
at the top and another on the left side. At the top of each vertical
column of holes is placed a card holder. This is made of light tin
turned up on the long edges--which are vertical--and tacked to the
board. Opposite each horizontal row of holes