Then say, I shall now take the letter away, and wish you to shew me concave and convex on one of your fingers; when they will bend the forefinger and point them both out on it.

Go on with the other letters in the same way: shew them the vowels after the consonants and analyze each one.

For example, A is formed of two inclined lines and a horizontal line to join them in the centre; and the top of that letter is an acute angle, and were a line placed at the bottom it would be a triangle.

A brass letter may be moreover shewn to be a substance: its properties may be described as hard, smooth, bright, &c., and its coming from the mineral kingdom may be noticed, and thus the instruction may be indefinitely varied.
The _power_ of letters may then be pointed out.

Ask them to spell M R, and they will give you the sound of R, or something like it, and so in reference to other letters.