over a number of years. This is not surprising, for the rate of flow of air is fairly critical. If the pump is not working fast enough the candle goes out; if too fast, the flame is sucked off the wick.
OT+-
FILTER PUMP
If a control experiment is performed without the candle alight, there is no measurable gain in weight in three minutes; that is, the gain is not due to absorption of atmospheric moisture and carbon dioxide. JAMESA. WENDEN CATERHAM SCHOOL SURREY, ENGLAND
Opportunity Knocking
To the Editor: I often think i t a pity that people set up such formidable objectives for teaching the sciences when they can be so simply expressed in the single word opportunityopportunity to study for a short time a subject +at can give our students understanding and appreciation of men and things in relation to themselves and others, and often there comes so great an appreciation of science itself that some of these seek a larger opportunity and decide they want or need more of these essential science facts. They are tomorrow's doctors, nurses, technicians, engineers, and scientists. GRETAOPPE
For a n Heuristic Presentation of Chemistry
To the Editor: May I offer a word of appreciation for Professor Babor's recent article on "The Sequence of Topics in General Chemistry?" I am gratified to note that Dr. Babor has gone back on the current vogue and has reverted to the older, less "logical" hut more teachable order of topics. I go even a little further. There is a thLory, sometimes called "Heuristic," that the developing individual human mind tends to pass through the same stages of concept and comprehension that the human race, as a whole, has followed-just as the human embryo passes through the rudimentary stages of biological evolution. I know of no serious effort to prove this theory: yet it is certain that the average adolescent does not think logically. Any teacher who has investigated the actual ways in which students finally achieve comprehension is likely to be astonished a t the curiously involved, inverted, and "back-door" or "intuitive" thought paths of the learner. It seems more than plausible that the average student will grasp the developing theory of any science more naturally and easily if the topics are presented in the historical order of their discovery. Lowry's "Historical Introduction to Chemistry" is an attempt in this direction. Not many of the fundamental theories of science have been discovered by the method of pure, logical induction. Proust proved the law of definite proportions, and had before him sufficient data to demonstrate the law of multiple proportions-the "logical" foundation of quantitative atomic theory-yet it never occurred to him to apply his figures to atoms. Dalton, groping around in the vast region of his imagination for some workable picture of the mechanical structure of gases, stumbled "intuitively" upon the idea of assigning fixed weights to elementary atoms; perceived that the idea would explain Proust's figures; saw, also, that if his idea was correct, there would have to be a law of multiple proportions, and proceeded to "discover" the law. The "logical" foundation of present-day chemistry is electronic, atomic-structure theory. Several able teachers have published texts starting from that viewpoint. In some cases, however, in the later editions of their books, they have felt constrained to revert to atoms and molecules as provisional fundamental entities of chemistry and put electronic chemistry one or two hundred pages further on. Any method, of course, can be taught with a degree of success if the teacher is enthusiastic about it, and has teaching ability. But a t least some highly intelligent and progressive teachers have abandoned their earlier ambitions and gone back to a less "logical" but apparently more practical order of topics. . . . GLENWAKEHAM
