Words in a language being made up simply of combinations of letters, it is clear that as long as only two differences are available, words can be built up by making the proper combinations according to the code. Any differences will do, and to this fact are due the possibilities for the exercise of the thinking powers, imagination, and skill on the part of children in this work. Lesson VI, for example, combines elements of instruction and play in an interesting manner. The transmission of words and sentences can be accomplished even without the use of objects, for two different motions of the fingers or hands will do; likewise two different sounds--in fact any differences perceptible to any of the five senses can be used. "Wig-wagging" as used by the U. S. Army Signal Service is based upon this Cipher. Thus many games can be planned which will have an educational value in training to a higher efficiency every faculty the child possesses. The lessons have been arranged in a sequence according to their increasing order of complexity, leading up gradually to the presentation of the possibility of sending hidden messages in an open communication without arousing any suspicion as to the presence of anything secret. In Lesson XIV the phrase "Biliteral Cipher" is made to contain the hidden word "Key" by the use of a capital letter for the _a_ form and a small letter for the _b_ form. Of course the differences between the _a_ form and the _b_ form can be made much less apparent than the differences between capital and small letters; in fact the differences can be made so small that they would be imperceptible to the casual observer, but it still would be possible to distinguish them. It is in this phase of the work that accuracy and care in the formation of letters may be taught, not only in script or handwriting, but also in printing, both of which are now fast becoming lost arts. Cipher writing, if properly taught, will give practice in penmanship that will be interesting and not onerous to children. The adaptability of the Biliteral Cipher to the manifold uses to which it can be put makes its pedagogical possibilities far-reaching; and the field for the exercise of the faculties of both teacher and pupil, parent and child, is one of the broadest, most instructive and entertaining that has ever been opened to the little folks of primary age. Any further information which the instructor may care to secure will be furnished on application to the Riverbank Laboratories. Dorothy Crain TRAINING THE EYE TO SEE That the faculty of sight needs training will be admitted by every reasonable person, but how best to give the eye this advantage is a question which has never been settled. An English hunter, the author of a book on Norway, gives some interesting hints upon the matter: