that two ships steaming along side by side are pushed towards each other by the water. Thus when a squadron of warships is maneuvering it is dangerous for one ship to attempt to pass close by another. In order to understand this effect it is helpful to consider the equivalent case of two ships standing still side by side in a stream which flows swiftly past them, as shown in Fig. 10. The velocity of the water is much greater in the region b between the ships than it is in the outside regions aa, and therefore the pressure in the region between the ships is less than the pressure in the regions aa, so that the ships are pushed towards each other. An effect similar to the attraction of two ships in a stream may be shown by suspending two light

balls side by side in the blast of air from an electric fan, as indicated in Fig. 11. The blast pushes the balls together.

Fig. 12 shows how a stream of liquid or gas flows around a flat plate PP. The velocity of the fluid is great at the point a, and small at the point b. Therefore the pressure of the fluid is great at b and small at a. This difference of pressure turns the plate in the direction of the curved arrows cd, thus bringing the plate into a position with its plane at right angles to the stream. This effect can be shown by placing a pivoted disk in the blast of air from an electric fan, or it can be shown by allowing a flat sheet of paper to fall through the air. The manner in which such a sheet of paper falls is indicated in Fig. 13. A piece of paper with its edges turned up falls as indicated in Fig. 14 without darting to and fro sidewise. This difference in the behavior of a plane surface and a curved surface in a current of air is exemplified by the difference in the behavior of the oldfashioned paper kite with a flat surface and the more recent

The water level between the two ships is lower than the normal water level of the

stream.

type of kite with a curved surface. The old-fashioned kite tends to dart to and fro sidewise, and it has to have a tail to counteract this tendency; whereas the kite which has a curved surface flies very quietly and without a tail.

The wing surface of an aëroplane is never flat as shown in Fig. 15, but curved as shown in Fig. 16. If the wing surface were flat most of the upward force would be exerted at the forward edge b as shown by the heavy arrow F and as explained

paper

'Β

Fig. 14.

Fig. 15.

Fig. 16.

in connection with Fig. 12. When the wing surface is curved as shown in Fig. 16 an approximately uniform upward pressure is exerted over the whole surface, as indicated by the arrows FFF in Fig. 16.

The curved flight of a spinning ball, as exemplified by the curve of an expert baseball pitcher, is an example of Bernoulli's Principle. To understand this effect it is best to consider the case of a spinning ball which stands still in a stream of air, instead of considering a spinning ball which moves forwards through still air, the two cases being exactly equivalent to each

other. Thus Fig. 17 shows the manner in which a blast of air flows past a spinning ball. The spinning motion of the ball causes the air blast to be turned to one side of the ball as shown, and the velocity of the air at b is much greater than the velocity of the air at a, therefore the pressure of the air at a is greater

than the pressure of the air at b, so that the air pushes the ball in the direction of the dotted arrow.

Figure 17 represents a spinning ball in a stream of air which flows to the left, and the effect is the same as if the spinning ball were moving towards the right through still air as shown in Fig. 18. The spinning motion of the moving ball in Fig. 18 causes the air to push sidewise on the ball in the direction of the dotted arrow, thus causing the ball to describe a curved. path.

The curved flight of a spinning ball may be shown very beautifully by throwing a ball of cork or pith by means of the device shown in Fig. 19. A fine thread is tied to the end of a light rubber band and wrapped around the ball. The rubber band is then stretched, and when the ball is released it is thrown for

light ball

fine string rubber band

stick

Fig. 19.

wards with a spinning motion, as indicated by the curved arrows in Fig. 19. This spinning motion causes the ball to be pushed upwards by the air as explained in connection with Fig. 18. A light ball may thus be made to curve upwards to the ceiling of a room, although the initial direction of its motion is horizontal. The motion of a "high foul" is an interesting example of the curved flight of a spinning ball. The ball strikes the bat as indicated in Fig. 20, and rebounds in the direction of the arrow I. At

ward flight, as explained in connection with Fig. 18. The catcher, judging from the early portion PP of the ball's flight, runs to point A expecting to catch the ball, but the ball turns inwards to the point B. This failure of a catcher in the case of a "high foul" is sometimes very amusing.

The curved flight of a "high foul" can be shown by throwing a small ball of pith or cork, or best of all an oak gall, into the air in a manner similar to the shooting of a marble so as to cause the ball to spin as indicated in Fig. 20.

RESULT OF EXPERIMENT TO DETERMINE CONTENT

AND APPEAL OF FIRST YEAR SCIENCE.

BY FAITH MCAULEY,

High School, St. Charles, Ill.

For two years we have been giving a course in elementary science at St. Charles. The introduction of this work was prompted by several things, foremost of which was the lack of the scientific habit of approach to a topic, evident in the second year pupils beginning botany or zoology; second, the feeling that there is fundamentally important material which should be the possession of each student irrespective of subsequent specialization; third, the conviction that such fundamental material would act as a natural gateway to subsequent work such as effective physiology, intelligent physiography, etc.

Without discussing the content or unifying element in the work, I shall give briefly, the results of two experiments.

By the first experiment we hoped to be helped toward an answer as to the suitability of the material chosen. The introductory work is based on air and water and so is largely chemical. In order to determine whether this material was as workable with first year pupils as with third, parallel examinations were given to the elementary science and chemistry classes, five out of the ten questions being the same for each group. Below is the result based on the five questions.

The above data would seem to indicate that the material chosen is as well adapted to the first year as to the third.

Second, wishing to be guided in formulating the work by the attitude of the students themselves, the class of last year was given the following questions:

1. Which subject in first year required most effort?

2. Which do you think was most profitable?

3. In which were you most interested?

The above results seem to me to suggest that elementary science may rightly have a place in first year work.

ASBESTOS IN THE UNITED STATES.

An International Industry.

The United States has for years led all other countries in the manufacture of asbestos goods, but until recently all the raw asbestos used has been imported from Canada, where there are nineteen quarries and mills, having a capacity of 8,250 tons of rock a day and employing in summer more than three thousand persons.

A feature of the asbestos industry of 1909 was a combination of Canadian producers in the Amalgamated Asbestos Corporation (Ltd.) and the formation of the International Asbestos Association, an organization including mine owners in Canada and manufacturers in the United States.

No asbestos of the higher grade (serpentine asbestos, or chrysotile) was mined in the United States until 1908, but in that year Vermont produced some chrysotile and in 1909 mined a larger quantity, amounting to nearly one twentieth of the Canadian output. Chrysotile asbestos has been mined in small quantities in Wyoming during the present year.