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minimum, and design the parts so as to attain the highest sensibility. The best relays are sensitive to the current of one ordinary dry cell acting through a resistance of 150,000 ohms.

One of the special features of the Slaby-Arco system is the tuning or syntonising of the receiving with the transmitting circuit. It is shown mathematically and confirmed by experiment that the total length of an oscillating wire correspond to half the wave-length of oscillations; each half of the wire or antenna is the fourth of a wave-length. Each wire excited by a sparking circuit has certain defined oscillations to which the electric waves it sends out into space correspond. These waves set up oscillations in the receiving antenna by induction. This receiving wire, from its size and length, is suited to a given kind of oscillation. If this be the same as that of the transmitting wire, it responds much more readily. The more complete the tuning the more complete the action. The tuning is accomplished by means of syntonising coils of wire and condensers. If the tuning is very accurate, multiple telegraphy from the same receiving antenna is possible, each system being tuned to its own transmitting circuit. Slaby was the first to give publicity to this form of multiple telegraphy. In December, 1900, he received two messages simultaneously from one common antenna. The wave-length of the first system was 640 m., distance 9.3 mi.; the second 240 m., distance 2.5 mi. A simultaneous recording of seventy-two words per minute was received.

For long-distance telegraphy Count Arco has devised a portable syntonning coil, by means of which perfect syntonism can be obtained without effecting other relations.

Although tuning will not prevent entirely interference by other systems, it is as yet the principal means of obtaining non-interference in wireless telegraphy.




The apparatus ordinarily used consists of an assemblage of parts similar to the one in the drawing, the length of air column being varied by raising or lowering the reservoir. I place the water supply stationary, above the tube (t), which is closed at bottom with a double perforated rubber stopper, through which pass two tubes of glass or brass, one of which is connected to funnel (f) with rubber tubing, the other to dish for holding water. Both tubes are closed with pinch-cocks marked p. c. in drawing.

The operator sits in front of apparatus with (p. c. 2) in left hand, and (p. c. 1) in right, and eye in line with the water level. He thus has perfect control of the column through the agency of the pinch-cock. Occasionally the water may be poured from the dish to the funnel.

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This experiment was suggested by Thos. Preston ten years ago but only recently has the suggestion been acted upon. The essential part of the experiment is a glass float so adjusted as to be but slightly heavier than water at o° C. In this illustration today I am using three floats of slightly different densities. The curve of density and temperature tells the story

of what happens.

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Beginning at o° C the glass is heavier and sinks but as the water warms the water grows heavier and pushes the float to the surface only to allow it to sink again after the point of maximum density is passed. Owing to the slight difference in density the floats do not rise at the same temperature. The following data are suggestive. The temperature is the temperature of the middle of the water:

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If we try to get the point of maximum density from this table, we find it at about 5° C. This is the result obtained by Depretz in 1840 by means of the water thermometer. The true maximum can be obtained only by a correction due to the expansion of the glass. However, the experiment illustrates very forcibly the fact that there is a point of maximum density.




One who undertakes to discourse on the value of literary models as a method of teaching composition has to encounter at least two varieties of objection. He finds that a considerable number of English teachers do not believe in training the student to follow models of any kind. Another class are not opposed to the use of the imitative principle, but they regard with suspicion any attempt to make the work of the high school student literary.

Addison tells us of the "condition of a good man that had one wife who took a dislike to his gray hairs and another to his black, till by their picking out what each of them had an aversion to, they left his head altogether bald and naked." When some of my listeners have picked the literary and others the imitative element out of the method for which I am to speak, my subject, too, may be altogether bald and naked.

A letter which came to me recently regarding the teaching of composition expresses these two objections in the form in which one commonly meets them. "I do not believe," says the writer, "in the use of literary models. 1 think the method lays so much stress on the mechanical, arbitrary side that instead of developing it would decidedly retard originality. I think it is too far from the actual life interests of the boy and girl, too advanced in literary ideal to be practical in its results. I think that it is of more value to the boys and girls and to the city and the country that they should be able to discuss potatoes, and wheat and threshing machines, and street cars and griddle cakes than it is that they be able to discuss in a superficial or even better fashion the latest or even the best in literature and art."

Let us consider first the objection that the imitative method hampers originality.

It is a commonplace of psychology that we find the imitative and creative impulses closely united in the child. He has a double personality. On the one hand he is slavish in imitating all examples set around him by his elders, and on the other hand he is self-assertive, that is, creative. Nature has joined these two powers together in the individual, in his physical, social and intellectual life. He begins his existence with but few acts of skill, and it is by imitating his elders that he acquires the further acts of skill to be found in his social environment. In the course of his effort to copy these models he finds that he consciously or unconsciously introduces novelties into his imitations. This is the beginning of invention,

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