was then fastened to the end of the large rope and drawn close up to the upper edge of the capital, and then, you perceive, they could easily hoist each other up. They did more, for they hoisted the English flag on the top, and then drank the bowl of punch, and won their wager."

"That is a very good story," said the vicar; "but I cannot help regretting that so much ingenuity and labour should not have had a nobler end to accomplish."

"There is some truth in that observation," said Mr. Seymour, "and I will, therefore, relate another story which shall be more congenial to your heart, and in which the kite will present itself in a more interesting point of view; for, instead of enabling the sailors to drink a bowl of punch at an altitude otherwise inaccessible, we shall find it engaged in rescuing them from the horrors of shipwreck."

"Pray proceed, papa."

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'No, my dear; upon second thoughts, I think it will be better that we should postpone the story until your return to the Lodge, when you shall read the account in 'Harry and Lucy.' But it has just occurred to me that I have been told that some of those marvellously lofty chimneys of steam-engine furnaces which you see in manufacturing districts, have been ascended for the purposes of repairs by precisely the same means as that employed by the sailors to reach the summit of Pompey's Pillar. On our return, I may this evening, or perhaps to-morrow more conveniently, take the opportunity of showing you some experiments in illustration of other cases of reaction occasioned by the air." "Shall we not return immediately?"

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No, my child; it would not be in my power to attend you at present. Mr. Goodenough will now accompany me on a visit to Major Barker, and do you remain and enjoy the amusement of your kite."

TOM

CHAPTER XXI.

A sheaf of peacock arrows, bright and keen,
Under his belt he bare full thriftily.
Well could he dress his tackle yomanly;
His arrows droopèd not with feathers low,
And in his hand he bare a mighty bow.

OM'S holidays were now approaching their close, as on the following week he would be required to resume his place at school. There still remained, however, a few bright days, during which he was to share the endearments of the affectionate circle at Overton Lodge; and it was upon almost the last of these that we might have seen him, in the company of his father and Mr. Goodenough, stepping across the lawn towards the terrace, where the younger girls had for some time been amusing themselves by playing at shuttlecock and battledore.

"Papa," exclaimed Fanny, "I have been considering whether there is any philosophy in the game of shuttlecock."

"There are two circumstances connected with its flight," re

plied her father, "which certainly admit of explanation upon scientific principles, and I should much like to hear whether Tom can explain them. The first is its spinning motion in the air; the second, the regularity with which its base of cork always presents itself to the battledoor, so that after you have struck it, it turns round, and arrives at your sister's battledoor in a position to be again struck by her, and sent back to you."

"I perfectly understand what you mean; but I really am not able to explain the motions to which you allude," said Tom.

"The revolution of the shuttlecock about its axis entirely depends upon the impulse of the wind on the oblique surfaces of its feathers; so that it is often necessary to trim the feathers of a new shuttlecock before it will spin."

"I understand you, papa: the force of the wind, by striking the oblique feathers, is resolved into a perpendicular force, as you explained to us when we considered the action of the wind upon the kite."

"Exactly. And having settled this point, let us consider the second, namely, how it happens that the cork of the shuttlecock always presents itself to the battledoor.”

"I should think," said Tom, "that the cork points to the battledoor for the same reason that the weathercock always points to the wind."

"Admirably illustrated!" exclaimed his father: "the cork will always go foremost, because the lighter feathers, presenting to the air a surface far greater as compared with their mass, will be more retarded in their progress. While we are upon this subject, I will introduce to your notice some contrivances which operate by this same principle. In the first place, there is the arrow can you tell me, Louisa, the use of the feathers which are placed round its extremity?"

"To make its head proceed foremost by rendering the other end more sensible to the resistance of the air," replied Louisa.

"Very well answered: that is unquestionably one of the objects of furnishing an arrow with wings; but there is also another

-that of steadying its progressive motion by rifling it, or causing it to revolve very rapidly round its axis. If you will look at this arrow, you will perceive that the feathers are placed nearly, but not quite, in planes passing through it. If the feathers were exactly in this plane, the air could not strike against their surfaces when the arrow is in motion; but since they are not placed

THE WINDMILL.

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perfectly straight, but always a little aslant, the air necessarily strikes them as the arrow moves forward. By the force thus produced the feathers are turned round, and with them the arrow or reed, so that a rotatory motion is generated; and the velocity of this motion will increase with the obliquity of the feathers up to a certain point, beyond which a further increase of the angle of their inclination to the axis of the shaft would diminish the effect. You will, therefore, observe that, in order to enable the feathers to offer the necessary resistance to the air, they must possess a certain degree of stiffness or inflexibility."

"It was on this account," observed the vicar, "that Roger Ascham, and other skilful artists in the days of archery, preferred, for pluming the arrow, the feathers of a goose of two or three years old, especially such feathers as drop of themselves; and the importance of this choice is confirmed by an observation of Gervase Markham, who says that 'the peacock feather was sometimes used at the short butt; yet seldom or ever did it keep the shaft either right or level.'

"That is intelligible enough," said Tom: "the feather of the peacock is so flexible as to yield to the slightest breath of air. But now, papa, as we are upon the subject of the arrow, do pray explain to us the action of the bow."

"I shall readily comply with your request before we part; but I am desirous at present of following up the subject before us, and of taking into consideration some other contrivances which owe their motions to the action of the air upon oblique surfaces." "Suppose," said the vicar, "you explain to them the action of the wind upon the sails of the mill."

"I should like to hear something about the windmill,” observed Tom; "and perhaps Mr. Goodenough can tell us who invented the machine."

"The invention is not of very remote date,” replied the vicar. "According to some authors, windmills were first used in France in the sixth century; while others maintain that they were brought to Europe in the time of the Crusades, and that they had long been employed in the East, where the scarcity of water precluded the application to machinery of that more powerful agent."

"I had intended," said Mr. Seymour, "to enter fully upon. the subject of the windmill; but I should require several models which are not yet in readiness, and as Tom's holidays have

nearly passed away, I must postpone the examination of the mill to some future opportunity, and content myself, at present. with an explanation of its sails. To understand why these sails revolve by the force of the wind, we must have recourse to the notion of resolved forces. It is evident that if a mill exposed directly to the wind had the planes of its sails perpendicular to the axle, they would receive the wind at right angles to their surfaces, and the impulse would simply thrust the axle longitudinally. But when the planes of the sails are set so that they slope a little away from the direction of the wind, the impact of the latter gives rise to a force which, resolved in the direction o! rotation, impels the sails, and thus the axle is carried round; for the four sails are all set obliquely in the same direction, and unite their effects. But if you will now come with me into the dining-room, I shall be able to exhibit to you an amusing toy which acts by the same principle as the windmill. I require some one to bring me the piece of pasteboard which lies on the library table."

Fig. 93.

明

Fig. 94.

The pasteboard was produced, and Mr. Seymour drew upon it a spiral, similar to that represented in the annexed figure (Fig. 93). The spiral was then cut out, and extended by raising the centre above the outer coils. It was now suspended upon a knitting-needle by applying the centre or summit of the spiral