to be able to name, _instantly_, the _Adjunct_ assigned to any
Compartment named in the right-hand column of the following Table.

Also he ought to be able to name, _instantly_, the _Compartment_
assigned to any Adjunct named in the left-hand column.

To make sure of this, he had better put the book into the hands of some
genial friend, while he himself has nothing but the blank Diagram, and
get that genial friend to question him on this Table, _dodging_ about as
much as possible. The Questions and Answers should be something like
this:--

pg025
TABLE I.

.----------------------------------------.
| _Adjuncts_ | _Compartments, or Cells,_ |
| _of_ | _assigned to them._ |
| _Classes._ | |
|------------|---------------------------|
| x | North Half. |
| x' | South " |
| y | West " |
| y' | East " |
|------------|---------------------------|
| xy | North-West Cell. |
| xy' | " East " |
| x'y | South-West " |
| x'y' | " East " |
.----------------------------------------.

Q. "Adjunct for West Half?"
A. "y."
Q. "Compartment for xy'?"
A. "North-East Cell."
Q. "Adjunct for South-West Cell?"
A. "x'y."
&c., &c.

After a little practice, he will find himself able to do without the
blank Diagram, and will be able to see it _mentally_ ("in my mind's eye,
Horatio!") while answering the questions of his genial friend. When
_this_ result has been reached, he may safely go on to the next Chapter.

pg026

CHAPTER II.

_COUNTERS._

Let us agree that a _Red_ Counter, placed within a Cell, shall mean
"This Cell is _occupied_" (i.e. "There is at least _one_ Thing in it").

Let us also agree that a _Red_ Counter, placed on the partition between
two Cells, shall mean "The Compartment, made up of these two Cells, is
_occupied_; but it is not known _whereabouts_, in it, its occupants
are." Hence it may be understood to mean "At least _one_ of these two
Cells is occupied: possibly _both_ are."

Our ingenious American cousins have invented a phrase to describe