´ a minute: thus, 50´ is 50 minutes; ´´, ´´´, ´´´´, denote seconds, thirds, and fourths; and the same characters are used where the progressions are by tens, as it is here by sixties.
∺ the mark of geometrical proportion continued, implies the ratio to be still carried on without interruption: as, 2, 4, 8, 16, 32, 64 ∺ are in the same uninterrupted proportion.
√ When used without a figure above it, indicates the square root, and is called the radical sign. Any other root is expressed by the index figure placed above the sign. √16 is the square root of 16, ∛27 the cube root of 27, &c.
≅ difference equal.
∹ the difference, or excess.
Q or q, a square.
C or c, a cube.
QQ, the ratio of a square number to a square number.
In algebraical work, authors should be very exact in their copy, and compositors as careful in following it, so that no alterations may be necessary after it is composed, the over-running of this kind of matter being troublesome and costly.