THE POPULAR SCIENCE MONTHLY.
have been well prepared, and which approach more or less to the level of his own; but to teach a class of little boys, to realize their difficulties and to appreciate their ignorance, to understand the perplexity which oppresses them in the presence of statements long since axiomatic to ourselves, require a mature and versatile intelligence, a mind which can communicate childish knowledge as readily and as joyously as it solves recondite problems; a combination of rare gifts with long and conscientious training.
And thus it is that the zeal for scientific teaching and the gathered scientific experience of the last fifteen years have only issued now in the books which form the subject of our notice. Scientific class-books hitherto have been either too difficult or too easy. They have been unavailable for beginners without the intervention of a practical teacher; or, in their effort to be popular and simple, they have abdicated half their value as instruments of educational discipline. In these books both extremes are avoided. Every stage of their teaching is based upon experiment; no law is enunciated till it has been proved. From first to last the student finds himself in immediate contact with Nature. His empirical knowledge of external things is systematized; simple every-day phenomena reveal to him their principles and rationale; he walks forth with a new eye to discern the meaning and the beauty of familiar sights and sounds, and with a mind upon the stretch for fresh discoveries. And, on the other hand, no previous training is essential to the teacher who adopts them as his guide. Any man, ignorant even of the first principles of chemistry and physics, yet fairly dexterous and intelligent, who will patiently master the books, and try each experiment for himself, is in a position to transmit their contents successfully and clearly. The officer may lecture to the soldiers of his regiment, the clergyman to the artisans of his parish, the national school-master to the children of his school. Managers of schools, deterred as yet from including science in their course through lack of teachers and of text-books, will find their difficulty removed. ... We tender them our hearty thanks for work which marks a stage in the advance of scientific education. Its lingering progress hitherto has been owing to. the want, not of zealous champions, but of united action. The labors of its advocates are now beginning to converge. The leaders of science and the leaders of education are drawing close together—on the one side eager to impart, on the other ready to receive, ad vice and guidance. By the publication of these books the most serious of the obstacles which have kept them separate is removed.
Length of Guns.—General Morin, in a discourse delivered before the Paris Academy of Science, noted this curious circumstance, that, though different kinds of powder may give equal speed to a projectile, they may differ very much from one another in the pressure they exert upon the walls of the cannon. He further remarked that all the grades of powder that have been tested undergo entire combustion, and consequently produce all their effect in pieces whose length is 12 times their calibre. But yet the greater part of the field-pieces in use have a length equal to 30 times their calibre. They might be cut down, therefore, without prejudice to their efficiency, and thus their portability would be increased.
Late Researches on the Gastric Juice.—The gastric juice of the human stomach has lately been made a subject of special study by Dr. Leube, of Erlangen, who gives the fruits of his work in an elaborate paper read at the recent Rostock Congress. He obtained the juice for his experiments by means of a tube introduced into the gullet. The gastric juice obtained from the stomach, empty and cleansed by an injection of water, is slightly acid, doubtless owing to the irritation caused by the injection and the contact of the instrument. Its digestive power is weak. In the course of his experiments with this fluid, Leube found that cheese is digested more rapidly than the albumen of a boiled egg, and the latter more rapidly than the albumen of a raw egg.
Experiments made with quassia demonstrate that this substance does not exert any special exciting action upon the secre-