The Practical Teacher

of the dogs, who are, generally, only too eager to rush upon their foe.

No sooner does one of them come within reach, however, than a sudden sharp stroke is delivered by one of the hinder feet, which, being armed with a long and sharp claw, are capable of inflicting very severe wounds. Indeed, instances are by no means unusual of a dog being completely ripped up by a single stroke from the terrible foot of the kangaroo. In this manner a kangaroo will often keep at bay a whole pack of dogs, their combined efforts being insufficient to drive the animal from its post of vantage.

These claws are so long, and strong, and pointed, that they are used as heads for spears. It seems hardly fair to use the kangaroo's claw for the purpose of killing the kangaroo, but the Australian is obliged to do so, just as the Esquimaux kill the walrus with a spear headed with walrus ivory.

Except as a last resource, however, the kangaroo seldom fights, preferring to trust to its fleetness rather than to the formidable weapons with which nature has provided it. When chased, it often evinces the most remarkable cunning in its attempts to throw its pursuers off the track-attempts which are not always unattended with success.

One of the most favourite of these stratagems consists in a sudden and violent leap at right angles to the track. The anima then lies quietly among the brushwood until the hounds have passed by its place of concealment, when it noiselessly makes off in another direction.

With such violence is this sidelong leap taken, that in more than one case the leg of the animal has been broken by the severe strain suddenly laid upon it.

One of these animals, which was brought to bay, actually seized with its fore-paws the dog which was leaping at its throat, sprang to a river that was within a short distance, and held the dog under water until it was drowned.

As a general rule, the 'boomer,' or male kangaroo, is alone useful for purposes of the chase, the female usually giving but little trouble to the hounds, and not unfrequently dying of sheer terror without receiving the slightest injury. When quite young, however, she will sometimes afford very fair sport, her wonderful speed earning for her the title of Flying Doe.'

The bounds by which the animal progresses are of really wonderful length, the more so when we consider the rapidity and seeming ease with which they are made. Mr. Gould tells us that the spring of a full-grown 'boomer' was found to measure exactly fifteen feet, and that the distances between the footprints were as regular as if they had been stepped off by a sergeant.

The power of making these extraordinary bounds is owing entirely to the structure of the hinder feet, which are exceedingly long in proportion to the remainder of the limb. Unless the animal be alarmed, however, it proceeds in a far more deliberate and somewhat clumsy manner, balancing itself upon its broad and powerful tail, and swinging the hinder limbs forward much after the fashion of crutches. It is often imagined that the large and powerful tail forms an important auxiliary to these hinder feet in making the lengthy bounds for which the animal is so famous. This, however, is not the case, that organ seeming to be only employed in supporting the animal when sitting erect, and in assisting it to retain its equilibrium while leaping through the air,

THE largest of the Macropida is the Woolly Kangaroo (Macropus laniger), so called from the peculiar texture of the fur, which bears a considerable resemblance to cotton-wool. In size, this animal considerably exceeds the last-described species, an adult male averaging as much as eight feet and two or three inches in total length.

From the common kangaroo it may be easily distinguished by the colour of the fur, which is of a reddish-yellow hue, changing to grey upon the head and shoulders. The toes are covered with short black hairs. A white patch is found at the sides of the mouth, and, in the female animal, extends as far as the eyes. This species is an inhabitant of Southern Australia.

NEXT upon our list of Marsupials comes the celebrated Rock Kangaroo (Petrogale penicillata), which is, among rocks and precipices, very much what our common native squirrel is among trees.

The rapidity with which the animal will make its way over seemingly impassable crags is said to be truly marvellous. Once amidst the rocky ground in which it delights to dwell, it can set at defiance its two chief enemies, namely, the dingo, or wild dog, and the native hunter, its wonderful speed and activity enabling it to traverse ground where pursuit is out of the question.

Even should the hungry native succeed in tracking it to its lair, he gains but little advantage thereby, for the rock in which its retreat is usually situated is generally of so hard a nature as completely to set at defiance the rude tools possessed by the savage hunter, while the various exits with which it is always provided allow the smoke to pass through without disturbing the inmate, should its would-be captor resort to the use of fire.

It is, indeed, very seldom the case that the rock kangaroo will allow itself to be captured without considerable difficulty, save and except upon the occasional instances when it basks in the sunbeams, and abandons itself entirely to the enjoyment of the genial warmth. Upon such occasions it is so completely absorbed in its luxurious occupation that it may be approached and slain with comparatively little difficulty.

Although selecting by preference rough and broken ground for its usual haunts, this kangaroo appears to be quite at its ease among trees, ascending and descending the trunks with considerable facility, provided that they be not perfectly perpendicular.

The rock kangaroo is a far smaller animal than either of its above-described relatives, a full-grown male only measuring a little more than four feet in total length. The tail is furnished at the extremity with a tuft of long bristly hairs, which has sometimes earned for the animal the title of 'Brush Kangaroo.' The fur, which is of a purplish grey hue, is of no great value, its texture being decidedly coarse, and unfitting it for use in the purposes for which the skins of its congeners are employed.

THE Brush-tailed Bettong, or Jerboa Kangaroo (Bettongia penicillata), is of very much smaller dimensions than any of the preceding animals, scarcely equalling, even when fully adult, an ordinary English hare in size. It is a pretty and graceful little creature, bearing a strong resemblance in general appearance to

the Kangaroos themselves, to which animals, indeed, it is very closely related. In many particulars, however, it differs from the Macropina already described, the head being short and broad, and the tail endowed with considerable prehensile power. The colour of the fur is a pale brown, pencilled with white, the lower portions of the body being of a somewhat lighter hue. The extremity of the tail, which is decorated with a tuft of longer hairs, is black.

This pretty little animal does not reside in crevices of rocks, etc., after the manner of the rock kangaroo, but constructs for itself a dwelling in a somewhat singular manner. Taking advantage of some natural hollow in the ground, it scoops out the soil until a convenient depth is attained. The next step is to cover this hollow with a roofing of grasses, etc., so arranged that it exactly coincides in height with the tops of the surrounding vegetation. This is so ingeniously managed by the animal that, except to the practised eye of the native hunter, which immediately detects the slightest inequality among the herbage, it is almost invisible, the work being so neatly performed that scarcely a sign betrays the presence of the cleverly constructed domicile.

The animal conveys the materials selected for her nest to the site of the intended dwelling in a somewhat curious manner. First procuring a considerable quantity of leaves, grasses, etc., she forms them into a kind of sheaf, round which she twists her tail, hopping off, thus laden with her burden, to the nest. As soon as the material thus collected is used, she sets off in search of a second supply, and so on. until the requisite quantity has been obtained.

This animal is extremely common in New South Wales, but, owing to its nocturnal habits, is comparatively seldom seen, except by those who go in search of it. In spite of its small size it is wonderfully active, and will travel over the ground at a really wonderful speed should it be pursued or otherwise alarmed. When hard pressed it has, like the kangaroo itself, a curious habit of leaping off suddenly at right angles to its course, and concealing itself in some crevice, in the hope of escaping the observation of its pursuer.

IN the Kangaroo Rat (Hypsiprymnus minor), or Potoroo, as it is termed by the natives, we have one of the transitional links between the Macropina and the animals composing the next group of the marsupials, the general kangaroo form and appearance being preserved, while the power of leaping, and also of manipulating food and other objects with the forepaws, is altogether wanting. It is true that the animal is able to sit upright, after the fashion of the kangaroos, supporting itself by a kind of tripod formed of the hinder limbs and the tail. Here, however, the resemblance ceases, the mode of progression employed by the potoroo consisting of a curious gallop, very different from the powerful bounds of the preceding

animals.

The title of Kangaroo Rat is due to the nature of the tail, which is covered with scales, between which proceed a number of scattered hairs. It is not a very large animal, the total length being only some twentyeight inches, of which rather more than one-third is occupied by the tail.

The Kangaroo Rat is tolerably plentiful throughout New South Wales, and, not being so exclusively noc

turnal in its habits as is the Brush-tailed Bettong, is far more often seen. It feeds chiefly upon roots, which it extracts from the ground by means of its powerful claws, which form very efficient weapons for tearing up the soil.

Owing to the nature of its food, the potoroo is a terrible nuisance upon cultivated land, often causing severe loss to the agriculturist by its ceaseless ravages. The potato seems to be a particular favourite article of diet with the animal, which continues its depredations day after day in spite of the attempts which are made to check its destructive proceedings.

THE Kangaroo Hare (Lagorchestes leporoides) is not at all unlike the animal from which it derives its popular title-colour, form, and habits being so remarkably hare-like that the name of kangaroo hare is singularly appropriate. The fur is close, hard, and slightly curled.

When alarmed, the kangaroo hare can run with the most marvellous celerity, often baffling even the best hounds by its wonderful speed, and also by the facility with which it doubles when closely pursued. Although usually progressing by means of a rapid gallop, it is by no means destitute of leaping abilities, and, should occasion require, will often execute the most wonderful bounds.

The kangaroo hare appears seldom or never to be found in the neighbourhood of the sea-coast, but seems to be confined to the interior of the country, where it is tolerably abundant.

With the kangaroo hare we must conclude our account of the members forming the group of the kangaroos, and shall in our next paper proceed to describe some further examples of this curious tribe of animals, which form one of the most interesting of all the great families into which the mammalia are divided.

BEFORE doing so, however, we will cast a glance at the marsupium,' or pouch, from which these animals. derive their scientific name.

Many zoologists doubt whether the name is a satisfactory one, because the pouch is nothing more than a fold of skin, and there are many undoubted marsupials in which the pouch is practically non-existent, a mere wrinkle marking its position. The peculiarities of the marsupial structure are more internal than external, and, moreover, belong more to the young than to the adult animal.

It is impossible to describe the structure fully without the use of many and elaborate diagrams; but I will mention one or two of the most remarkable details.

No matter how large or how small the marsupium may be, the marsupial bones are always present. Even in the duck-bill, or platypus, and echidna, the marsupial bones are present, though the animals are not in any respect marsupials, but belong to a totally different order. Moreover, the marsupial bones are found in both sexes, though, of course, the male possesses no pouch.

Now we come to a very remarkable structure in the immature marsupial.

When introduced into the pouch it is affixed to one of its mother's teats in such a way that instead of receiving the teat into its mouth, its head seems to be drawn over the teat. At this period of life the young

one has not sufficient muscular power to enable it to suck, and the milk is continually forced down its throat by the compression of certain muscles peculiar to these creatures.

Now, if the structure of the young marsupial-say a kangaroo-were like that of other mammals, the little creature would be choked by the flow of milk; so the entrances to the respiratory and nutritive organs are separated by the modification of certain portions of the throat into a valve, which permits the milk to flow continuously down the throat while the channel of respiration is kept open.

The structure of this portion of the immature marsupial is almost identical with that of the whale tribe. (To be continued.)

"How I Teach Elementary Science.'

BY RICHARD BALCHIN,

Head Master of the Gloucester Road Board School, London.

FOURTH-SCHEDULE

'PARALL

MECHANICS.

SUBJECTS:

ARALLELOGRAMS of forces and of velocities.' This somewhat ambitious title would lead many to consider that the subject treated of was rather outside the limits of elementary instruction. Nothing, however, ought to be so considered which is fairly within the mental capacity of our scholars. And that this subject can be grasped by ordinary fifth and sixth standard boys, I have had abundant proof. I may mention, as a fact, that on the occasion of my giving the first lesson upon it, I asked a boy to come out and draw a line to show the direction of the resultant of two forces whose directions I had indicated on the blackboard; and the lad drew a line which I found, on completing the parallelogram, to be exactly coincident with the diagonal; so clearly did he perceive the nature of the subject. The truth is, the general principles or laws which are observed in the workings of nature around us, can be made clear to boys, just in proportion to the clearness with which the teacher himself perceives those laws. I am attending a course of lectures by Professor Seeley, and I cannot but note the enormous difference between his demonstration of a truth and that of our ordinary certificated science teachers. When listening to some of the latter, how soon it becomes manifest that their knowledge of the subject reaches just as far as the last page of the sixpenny text-book, and no farther.

Instead of reproducing a lesson, I will, in this article, endeavour to make clear what is meant by parallelogram of forces. Force is that which produces motion. It is measured by the amount of momentum it communicates. Momentum is compounded of mass and velocity. Weight is a measure of mass. Velocity is measured by the space passed over in a certain time. Now all those truths must be entirely understood before pupils are able to grasp anything concerning parallelogram of forces. It must here be understood that we speak of mechanical force only, not of heat force, or electric force, or chemical force. Let us take a mass of matter weighing 4 lbs. Let the number 4 represent such mass. It moves at a velocity, say, of 3 ft. per second. Good. Now we

will compound the mass and velocity. Multiply 3 by 4, answer 12. Then 12 is a number which represents the momentum of a certain moving body. But the momentum of a body is a measure of the force which has communicated that momentum. Therefore, the number 12 may stand to represent a force. Again, take another mass weighing 3 lbs. Let its velocity be 2 ft. per second. Then the number which will represent its momentum will be 6, which may represent the force that has communicated this momentum. Here, then, we have two momenta, represented relatively by the numbers 12 and 6; and we say the first momentum is double of the second. Also we have two forces represented relatively by the same numbers. I have entered into these preliminaries somewhat in detail, because I so frequently hear and read such phrases as the following:-let a force of 4 lbs. act;' 'let the line AB represent the direction of a force of 12 lbs.,' and so on. Now are not such statements misleading? What is a force of 4 lbs. ? Can there be such a thing as 4 lbs. of force? I cannot conceive of such. Of course, when we wish to represent the relativity of different forces, we may let numbers or lines stand for their magnitudes or intensities.

If two forces of equal magnitude act simultaneously from exactly opposite directions upon a given point, they entirely neutralize each other; or in more correct language they are entirely converted into a resultant of heat force; with which at present we have nothing to do.

If two forces, from different but not exactly opposite directions, act simultaneously upon a certain point, the resultant, both as to direction and intensity, may be represented by the diagonal of a parallelogram whose sides represent respectively the two forces. This is a statement of the parallelogram of forces. I need not, however, proceed further with the subject, as all the ordinary text-books fully explain it.

This article concludes the series on the methods I have adopted for teaching the Fourth Schedule Subject, 'Mechanics.' I trust that those of my readers who have not yet taken up the subject as a 'special' will be induced to do so. Not that they will neces sarily follow the lines I have laid down, for it is a subject that admits of an endless variety of treatment. In those articles I have confined myself more to the principles involved and of the methods of demonstrating those principles, rather than to their application to any of the practical businesses of life. But if I taught in a manufacturing centre, I should certainly arrange a syllabus for mechanics that would bear intimately upon the special industry of the locality. Suppose, for instance, my school were in Bermondsey. The syllabus should be framed so as to include the structure of skin, the nature of the various skin-coats of the pachydermata; something respecting the natural history of those animals whose hides yield leather; the chemistry of tanning, including the nature of tannic acid, and its action upon the gelatino-fibrous substance of the true skin; the sources of 'tannin,' whether as barks and other raw parts of trees, or as extracts such as 'gambir,' 'japonica,' etc. All these subjects might be taken in addition to the elementary principles of natural philosophy given in the code. And I am quite convinced, no inspector would object to such a syllabus, although it would not be at all points strictly coincident with the official syllabus. If

my school were at Burton-on-Trent, then I would arrange the work to include the scientific principles involved in brewing; and not a boy should leave my sixth standard without having the fact demonstrated beyond all manner of question, that the main business of the brewer was to utterly spoil vast quantities of valuable barley. To such an extent may we impart what is generally understood as technical knowledge. Still, however, we must not lose sight of the fact that science-teaching in our schools should always be educative rather than technical. That our chief work is not so much to turn out good tanners and brewers as to develop that general intelligence which will surely prove to be the primary element of success in whatever position of life our scholars may hereafter find themselves.

(1) Reduce a million oz. to tons.

Ans. 27 ton 18 cwt. o qr. 4 lb. (2) Reduce 1 ton 2 cwt. to lbs. Ans. 2464 lb. (3) A man earned 24 shillings weekly. He spent 19s. 7 d. a week. How long would he be saving £6 10s. 4d.? Ans. 29 weeks, and 3s. 5d. left. (4) £18 19s. 71⁄2d. x 621. Ans. 11,787 7s. 1d.

STANDARD V.

(1) Find by practice the value of 9017 suits at £3 16s. 4d. each. Ans. £34,414 17s. 8d. (2) A grocer bought 5 cwt. 2 qrs. of tea for £71 17s. 4d., of which 7 lbs. were spoiled. What would he gain or lose by selling the rest at 2s. 74d. a lb.? Ans. £8 1s. 3 d. gain.

(3) A bill:-1 3 lb. of cheese at 8d. a lb., 3 boxes of figs (2 lb. each) at 7d. a lb., 4 doz. oranges at 1d. each, 9 boxes of tapers at 2s. 3d. per dozen boxes, lb. of tea at 4s. 4d. a lb., and 17 lb. of bacon at Iold. a lb. Ans. 1 19s. 24d. (4) A man who works 10 hours a day does a piece of work in 4 days; how many hours would he have worked each day if he had taken 8 days? Ans. 58.

7421 390

7031 Ans.

STANDARD VI.

(1) Find the value of 3 + 21 +43 +18+2 of 3 of 1. Ans. 8.

(2) After spending of my money, I have 7s. old. left. How much had I at first? Ans. 9s. 9d. (3) Add together 75 of 20s., 75 of a guinea, 3 of a crown, and 125 of 24s. Ans. 1 17s. 6d. (4) Find by practice the value of 36 cwt. 2 qr. 14 lb. of spice, at £7 11s. 6d. per cwt.

Ans. £277 8s. 8d. (5) If a man can walk a certain distance in 1 hr. 18 min. 45 sec. by taking 76 steps a minute, how many steps a minute must he take to walk the same distance in 1 hr. 3 min. ? I Ans. 95. (6) Find the value of 1, and of 1÷, and reduce each answer to a decimal.

Ans. 70129+; 2'22727.

Grammar,

STANDARD III.

Select nouns, verbs, adjectives, adverbs, and pronouns, in the piece given for dictation.

(Analyse and parse the words in italics.)

(A) There in the shadow of old Time

The halls beneath thee lie,

Which poured forth to the fields of yore
Our England's chivalry.

(B) How bravely and how solemnly

They stand 'midst oak and yew, Whence Crecy's yeomen haply formed The bow in the battle true.

FEMALES.

1. Make out the following bill:-81 lbs. tea, at 25. 11d. per lb.; 99 lbs. coffee, at 1s. 74d. per lb. ; 54 lbs. cocoa, at Is. 5d. per lb.; 243 lbs. rice, at 2 d. per lb. ; 31 lbs. 8 oz. butter, at Is. 10d. per lb. ; 63 lbs. loaf sugar, at 74d. per lb.; 108 lbs. moist sugar, at 34d. per lb. ; 38 lbs. 4 oz. bacon, at 10d. per lb.; 55 lbs. 2 oz. cheese, at 8d per lb.