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PHYSICAL GEOGRAPHY IN THE UNIVERSITY.
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ful an analysis as is given to the forms of the land; but they cannot be traced here for lack of space.

Illustrations of the deductive scheme.—However much the advance of a deductive scheme of study may be aided by reference to concrete illustrations during its progress, its statement should be abstract, in order to emphasize the essentially deductive side of the study. It is difficult to follow such a method without artificial airds. Hence, in discussing the theory of the tides, a model of certain theoretical tidal circles was introduced for the convenience of definition and argument. It was found to be an effective aid in reaching certain geometrical consequences that follow from the rotation of the earth on an axis that is not coincident with the axis of the tidal circles. This model was an illustration of the same order as the diagrams employed in text-books on geometry. In the same way, a series of some thirty rough paper reliefs, constructed several years ago to illustrate a course of lectures to teachers under the auspices of the Boston Society of Natural History, are introduced to aid in giving clearness to the conception of the geographical scheme. They are roughly made; hardly better than blackboard diagrams, except in having three dimensions; yet they certainly serve a good purpose as aids in following deductive statements. Being two or three feet in length and yet light enough to handle easily, they are frequently brought into the lecture room, although they are used chiefly in the laboratory, where they can be examined and described deliberately. Nearly all the points thus far mentioned are illustrated in one way or another by these models; but I can here give account of only a few of them.

While occupied with the first considerations of the cycle and its systematic variations of relief, both in intensity and variety, use is made of three simple models, which are found to be of particular value in fixing the fundamental ideas. The first shows a broad upland, traversed by a main river with a few branching streams, all in valleys of the canyon type. The form of the second is well diversified, there being about as much of lowland in its wide open valleys as there is of upland on its well separated

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