The reason that the different characteristics of tracks are not observed by the untrained eye is not because they are so very small as to be invisible, but because they are--to that eye--so inconspicuous as to escape notice. In the same way the townsman will stare straight at a grouse in the heather, or a trout poised above the gravel in the brook, and will not see them; not because they are too small, but because he does not know what they look like in those positions. He does not know, in fact, what he is looking for, and a magnifying glass would in no wise help him. To the man who does not know what to look for, the lens may be a hindrance, because it alters the proportions to which his mind is accustomed, and still more because its field is too limited.--Youth's Companion. LESSON I This lesson is intended to teach the code or key. Attention is called to the mathematical regularity of its construction, which will enable the teacher to demonstrate it in a very simple manner. First write the column of numbers from 1 to 24. Then opposite number 1 place five red circles in a row. Under the last one in this row, and on a line with number 2 place a blue circle, and continue alternating red and blue down the column. Then under the 4th red circle in the 1st row place another red one, then two blue ones, alternating 2 reds with 2 blues down the column. In the 3rd column the reds and blues alternate in sets of four; in the 2nd column, in sets of eight, and in the 1st column, in sets of 16. Since only 24 combinations are necessary, the last eight of the possible 32 have been omitted. Now opposite these 24 combinations place the letters of the alphabet in regular order, remembering that I and J, U and V are used interchangeably. To facilitate the use of the code the red and the blue circles may be designated by small _a_ and small _b_ respectively. The right hand section of this lesson gives the code worked out on this plan and makes future reference easy. In all the succeeding lessons one form (whether it be blocks, beads, yarn or what not) will be called the _a_ form, and the other will be called the _b_ form. On account of the nature of the code, the _a_ forms always predominate; and in getting together materials for this work, the teacher should be guided accordingly. [Illustration: