The popular educator

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the hill, and then drives it over the scarp from в to c. The sands | the Nile to the Atlantic. Its sandhills not only reach the which find shelter between B and C remain stationary for some Atlantic, but they are prolonged even to the bed of that ocean, time, but the grains which have been driven over the scarp B, where they form sand banks composed of grains driven to the are again blown up to the scarp of a next hill, and so on from sea by the powerful east winds, which blow in that district for one hill to another in succession. In this manner a series of nine months in the year. sandhills is formed, at first, and then all the sandhills are put in motion, according to the force and the constancy of the winds, and the dunes advance at the rate of sixty and seventy feet per annum. Fig. 76.

At the equinoxes, these easterly winds blow into a hurricane, take up immense bodies of sand, and drive them along in clouds so thick as, at midday, to produce the darkness of night. represented in fig. 76. but upon a scale immensely large. The sand is heaped up in waves and ridges like those The very atmosphere itself is sand, and the sandy waves are driven onward with fearful rapidity, till whole caravans, that travel in their line, are overwhelmed and destroyed by them. During such a sandstorm, the heated air is like red vapour, and the setting sun looks like a volcanic fire. Some parts of these deserts have large and shallow salt lakes; other portions are plains covered over with thick incrustations of dazzling salt. The particles of this salt are taken up by the whirlwind, borne aloft by the gale, and flash in the sun like diamonds.

The effects of the encroachment of drifted sand, contemplated upon an extensive scale, are well developed in the changes which have taken place in the physical conformations of the Land of Egypt. It is well known that fertile districts of this

The formation and the advance of Sandhills and Dunes. The phenomena of moving sandhills, or, as they are some-country, lying to the west of the river Nile have been extentimes called sand floods, may be advantageously studied on sively invaded by sterile sands, which have been driven upon many parts of the coasts of Portugal, France, Belgium, Hol-them from the deserts of Libya by strong westerly and northland, and England, where there are numerous villages that are westerly winds. almost, or entirely, overwhelmed and entombed by the advance and encroachment of sand drifted by strong winds. Some of the best examples of the operations of sandfloods are to be seen in Morayshire, in the north of Scotland. There, to the west of the river Findhorn, was once a fertile district ten miles square, which was called the granary of Moray; but it has been, for nearly two centuries, inundated with sand floods driven by the east winds, so as to be now a sandy desert. Of these sands a great quantity was driven to the river Findhorn, which bore it down to its junction with the sea, where the sands form so firm a bar as to prevent the stream from entering the ocean. The river was then obliged to cut för itself a new channel, and the people of Findhorn had to remove their town from the east side to the west bank of the stream. Even to this day, the sands, borne down by the river, form so high a bar as to prevent the entrance of large vessels.

In another part of Scotland, along the west coast of the outer Hebrides, the bottom of the sea appears to consist of sand, with a few interruptions of rugged rocks. These sands are constantly drifting, so as to submerge a large tract of good land under sand hills. These sands consist chiefly of shattered and comminuted shells, apparently of the same species as now live in the neighbouring sea. The sand is, of itself, rather coarse, but such is the action of high and furious winds upon it, that by rubbing the particles of it against each other, a sort of small and almost impalpable dust is formed, which at a distance resembles a cloud of smoke. In this form, it is frequently seen driven upwards of two miles into the sea, where it descends like a thin white fog.

The sands drifted from Libya have already destroyed a great number of cities, once very celebrated in Egypt, such as Abydos, Memphis, Bahnasa, and a whole tract of country from Saccara to Abu Rehe. The ruins of some of these towns and villages are still to be seen. These inundations of sand have taken place even since the conquest of the country by the Mohammedans, for the summits of the minarets of some of their mosques are seen projecting out of the sands. In walking over these sandy wastes, and striking our foot against the pinnacle of some house or temple, it is melancholy to reflect that you are treading on what was once a scene of high cultivation and flourishing villages.

M. Denon has remarked that, were it not for a ridge of mountains called the Libyan Chain, which borders the west bank of the Nile, and forms, in the parts where it rises, a barrier against the invasion of sand, the shores of the river on that side would long ago have ceased to be habitable.

Some scientific writers have, with Sir. G. Wilkinson, asserted that the annual increase of the alluvium of the Nile was gaining ground on the western sands; but Capt. Newbold has demonstrated that upon the whole the encroachment of the sands is increasing. This advancement of the sands was naturally to be expected, when we consider that the westerly and north-westerly winds blow during nearly nine months in the year, which incessantly drift the sands from Libya towards Egypt; and that since the age of the Pharaohs, the artificial checks opposed to the progress of sandhills by certain plants and other means, have been greatly diminished by the want of industry, agriculture and population. But the most satisfactory proof of this encroachment of the sand upon cultivation, is the fact that, both in Upper and Middle Egypt, trees appear to grow out of the sandy waste; but, as they are traced downwards, their roots are always found embedded in the sediment once deposited by the Nile and now covered by drifted sand, as represented in fig. 77.

CUVIER, in his "Theory of the Earth" has shown that in districts much exposed to certain prevalent winds, the advance of these sandhills before strong gales and hurricanes is irresistible. He mentions that, in his day, there were ten villages on the shores of the Bay of Biscay that were threatened with destruction. It seems that one of these villages, Mimisan, has been for more than twenty years striving against the encroach- The progress of the sands as indicated by this tree is further ment of sand dunes, and that, in its neighbourhood, one sand-proved by several facts. Not only have many buildings of hill in particular, which was more than sixty feet high, might ancient Egypt been overwhelmed, but even ruins, that have be almost said to be seen to advance. Their progress not only been partially cleared, are again much covered with sand. The drives lakes backwards upon cultivated fields and villages, but great Temple of Abusambel, discovered by Burckhardt was it also changes the course of rivers. He supposes that, if they almost buried with sand drift to a great depth. Belzoni cleared travel at their present rate of about twenty yards per annum, away thirty-one feet of this deep drift to enable him to arrive at they will reach and overwhlem Bourdeaux in two thousand the entrance. Since then the sand has commenced to reinvest it. years. The great Sphinx which, thirty years ago, was disinterred from The grand theatre for witnessing the effects of wind in the sand in which it was buried up to the neck, is again covered production of sandstorms and sandfloods, is some extensive up to the shoulders. Plains and even mountains near the sandy desert that covers some thousands of square miles on the ancient town of Dimay, have been overwhelmed with vast surface of the globe. Such a theatre is presented in that track-mounds of sand. Every traveller can almost see its advance less ocean of sand, called the Sahara desert towards the nor- on Koum Omboo, Benisuef, and Tapta. Also on the steep thern part of Africa. This sandy waste covers an area of about ridges, on the western side of Fayoom, it has drifted so much eight hundred thousand square miles, extending almost from as to cover extensive ranges of the desert mountains to such a

depth, that only their summits and a few of their craggy pinnacles are visible above the undulating waste.

In the course of centuries these blown sandfloods will materially alter the aspect of the valley of the Nile. So long as the prevailing winds blow from the north and the north-west, or until the supply of sand in the Libyan desert be diminished or become exhausted, the western parts of this valley must suffer from sand drifts. There are two or three physical circumstances that are likely to tend to retard this encroachment. The surface of the Libyan desert is very rugged, having many Fig. 77.

This is curious enough: but it is more curious still, to find that these sandy bones turn out to be real and true vegetable plants. They are very rarely solid. Their centres are either hollow, or are filled up with a granular matter that is of a blackish colour. The form of these blackish granular particles is that of the oolite, or Bath stone. The outer crust of these cylinders is composed chiefly of a large proportion of sand, and a small amount of calcareous matter supplied by shattered shells. In many of the larger specimens, the incrustation contains fraginents of iron stone, and pieces of quartz about an inch square.

That these ramifying cylinders are real incrustations of plants that have decayed in consequence of being incrusted with blown sand, is proved by the different degrees of change that has taken place in the internal parts of different specimens. In some the organized tissue of the plant remains sufficiently distinct to verify its vegetable nature. The nearer you go to the sea, the more instances will you see of the different stages of the incrustation. You may see the very commencement of it taking place in some of the large fuci, or sca-weeds, which strew the shore.

Vegetable substances in similar situations were found to have undergone similar changes by M. Peron, in Australia. He thinks that the matter of the sea shells has been chemically decomposed, and that then it forms a cement with the sand; that the vegetable matter of the plant also becomes altered, and

A Tree imbedded in A, the Alluvium of the Nile, covered by B, the is finally replaced by the sand with which the different winds

Drifted Sand.

deep ravines and abrupt cliffs. At the depth of these hollows, and checked by these almost vertical cliffs, the sand collects and is detained for an indefinite period; and in this manner, furnishes a barrier against its own progress. As powerful gales drive the sand towards the east, the escarpment of the hills on the east side of the river prevent its further progress in that direction, and causes much of it to fall into the stream of the Nile, which carries off the lighter particles towards the sea. The heavier particles of the sand falling to the bottom, tend to raise the bed of the river, which will cause the waters to extend their alluvium further and wider, until it encroaches, as it actually does in many places, upon the drifting sand. I shall close this lesson by relating a few very curious phenomena that have resulted, in the surface of the earth, from

the combined actions of wind and sand.

Near Messina, in Sicily, drifted and loose sands have become so indurated as to supply a good quarry of building stones. Several portions of this mass have been excavated for this purpose. But the excavations which are made by the quarry; mer are, in the course of some years, again filled with sand which the winds drift into them. This sand becomes consolidated, and is also, in its turn, quarried for building materials.

On the coast of the Great Canary, there is a remarkable formation of limestone and sandstone, that is the result of wind action. Between the town and Isleta, the ground abounds with light fragments of broken shells, and comminuted and rounded grains of the basalt and trachyte rocks of the island. The violent winds of the north, take up these particles, drive them over the narrow tongue of land of Guanateme, so as form dunes of from thirty to forty feet high. The water behind these dunes acts upon the sand, and unites it into a compact mass. During the greater part of the year, this water is 77° Fahr.-a temperature which greatly promotes its action on the calcareous particles. The sandstone is a real oolite, like Bath stone. Most of the grains composing the stone are round and calcareous; the enlcareous matter surrounding a nucleus of trachyte, basalt, or a diminutive fragment of a shell.

At the Cape of Good Hope, a little to the east of Simon's Town, there is a large sand bank rising from the sea, to the height of a hundred feet. This sand hill is composed of broken shells and grains of sand, and is formed by having been thrown up by the south-east wind. In this sand hill there are numerous cylindrical bodies, which have much the appearance of bones that had been long bleached by the atmosphere. Many of them throw out branches like those of a shrub, cr small tree. Some of them, plant-like, rise out of the surface soil, as if they were so many vegetating bones actually in a state of growth, and putting forth branches that ramify from a stem beneath, that is thicker than themselves.

have invested it. The process leaves nothing to show its origin but its plant-like form.

In one part of this lesson, I mentioned that at the Hebrides, clouds of impalpable sand dust were driven, in the form of white smoke, some two miles into the sea. This appearance is witnessed in many parts of the world. In the heated districts bordering the Red Sea and the Nile, numerous little whirlwinds take up a large quantity of the finer superficial sands of the desert, and even small marine, land, and fluviate shells, and seeds of plants, which they transport and distribute ir all directions. In the Red Sea, the deck and shrouds of ves els are sometimes found covered with fine sand blown from the Egyptian desert. There is no doubt that these impalpable sands are transported completely over the gulf of Suez, even so far as the groups of the Sinai mountains. This will probably account for the singular musical sounds which are heard on the western slope of the mountain of the Bell, near Sinai. It arises from the motion which the wind gives to the fine sands which covers the sides of that mountain. The sound is thus accounted for by Seetzen and Ehrenberg. Mr. Darwin mentions a similar phenomenon in Northern Chili at a mountain called El Bramador.

LESSONS IN ARITHMETIC-No. XXVII.

COINS, WEIGHTS AND MEASURES.

IN our last lesson, we gave a full account of the acts of Parliament which produced the change in our weights and measures during the second quarter of the present century. Subsequent to the passing of these acts, other two acts were passed, one in 1834, and another in 1835. The object of the former act was to legalize the use of weights and measures differing in shape from the models proposed in the acts cited in our last lesson, and to abolish the use of Heaped measure, besides making better arrangements for carrying the provisions of the said acts into effect. In this act, the use of the stone of fourteen pounds Avoirdupois was fully recognised, and that of eight pounds Avoirdupois, which had been used in London, was abolished. The distinction between Avoirdupois weight and Troy weight was also recognised and allowed; the latter being employed in the sale of gold, silver, platina, and precious stones, as well as in the sale of drugs by retail. Sales by the Winchester bushel and the Scotch ell were declared illegal, and liable to fine and confiscation. Power was given to inspectors of weights and measures; verification of these enforced; forms of convictions for infraction of the act given, and penalties appointed; and lastly, a schedule of fees for examining, comparing and stamping weights and measures, appointed for the United Kingdom.

In the subsequent act, of 1835, that of 1834 was repealed, and new provisions were made instead thereof. These pro

visions, however, as far as the standard weights and measures | body is two-fold. Besides, there are two sexes in the whole of are concerned, were essentially the same as before; but some the animal and vegetable world; and numerous transactions latitude was allowed for the sale of articles in vessels not repre- in the sale of articles are conducted by pairs. Nevertheless, sented to the purchaser as imperial measures. Heaped measure independently of these considerations, we find that, in actual was still abolished; but sale by weight was permitted instead; business, almost every thing is measured by halves, quarters, and in the article of coal it was especially enforced. The eighths and sixteenths, not to speak of the parts below these, stone of fourteen pounds Avoirdupois was also recognised in proceeding according to the same law of progression; when we preference to any other weight, and considered as Imperial. wish to ascend the scale, we go on doubling, quadrupling, ocWeights made of lead or other soft materials were strictly tupling, &c. that is, doubling every time till we reach the numabolished; the mode of appointing inspectors was prescribed, ber or quantity to which we desire to attain. The binary and penalties for the infraction of the new regulations were system then seems to be the most natural, if we attend to the appointed. The powers and duties of inspectors were more actual practice of mankind. In this, of course, we speak of clearly defined, the mode of defraying their expenses ap- weights, measures, and coins, in their actual use in business. pointed, and forms of suing for penalties prescribed. A new Thus, in coins, we have the sovereign, the half-sovereign or schedule of fees for examining, comparing and stamping was angel, the quarter-sovereign or crown, and the eighth of a given, and the whole act was made more imperative than any sovereign or the half-crown; next, the shilling, the half-shilling of the former acts. It is under this act that we now carry on the or sixpence, and the quarter-shilling or three-pence, with the daily transactions of business throughout the United Kingdom; double shilling or florin; to this might be added, for the conand with the exception of Heaped measure, which is abolished, venience of the community, the quadruple shilling or double florin, and the sale of coal, culm, &c. by weight, which is enforced, which would be the four-shilling piece. It is true that the every thing remains the same as given in our last lesson. florin was coined with the view of introducing the decimal

The loss of the Standard Weights and Measures by the burn-system into our coinage, because it is the tenth part of a pound ing of the Houses of Parliament in 1834, occasioned the appointment of a Royal Commission "to consider the steps to be taken for the restoration of the Standards of Weights and Measures." The report of this Commission was presented to both Houses of Parliament by command of the Queen in 1841; and since that period, we believe nothing has been done to affect the operation of the act of Parliament of 1835, relating to the use of our present weights and measures. In this report, the Commissioners describe the state of the Standards recovered from the ruins of the House of Commons, as ascertained by their inspection of them, made 1st June 1838, and declare that the legal Standard yard referred to in preceding acts is, for the purposes of comparison, completely destroyed; that the legal Standard Troy pound is lost; and that steps must be taken for making and legalising new Standards of length and of weight.

The commissioners next declare their entire disapproval of the methods appointed in the acts of Parliament for the restoration of these standards; they then suggest that copies be made of accurate existing copies of the original standards; that these be legalised as the true standard of weights and measures; and that no reference be made to any natural basis or standard, such as the pendulum, in future. They recommend that the standard of weight be made a certain piece of metal or other durable substance; that the standard of capacity be defined by the capacity [that is, the vessel], which, under certain circumstances of the barometer and thermometer, contains a certain weight of distilled water; but that it be in no way defined by reference to the standard of length.

The commissioners also recommend that the Avoirdupois pound, of 7000 grains, be adopted instead of the Troy pound, of 5,760 grains, as the standard of weight; and that no change be made on the standard of length, viz. the Imperial yard. They also recommend that no standard of capacity be constructed; but that the definition of the Imperial gallon, as the capacity [or vessel which contains ten pounds [Avoirdupois] weight of distilled water weighed in air at the temperature of 62° Fahrenheit, the barometer being at 30 inches, be retained.

The next subject of recommendation which the commissioners take up, is the general question of the introduction of the Decimal Scale into the moneys, weights and measures of this country. On this subject we entirely differ from the said commissioners, and from several eminent scientific men who have expressed their opinions repeatedly in public. We confess that, at one period of our life, we were converts to this new-fangled doctrine of the first French Revolution; and we thought, of course, that because men had ten fingers, and ten toes, there was a double reason for adopting the decimal system of division; but we have seen the folly of this; and notwithstanding the upstart pride of the present age, we do believe that age gives wisdom, and that the hoary head is a crown of glory, if it be found in the way of righteousness. If we are to be ruled in this matter by numbers, the doubles, or the binary system, will have the preference; for men have two legs, two feet, two arms, two hands, two eyes, two ears, two checks two nostrils, two jaws; and almost every organ in the

or sovereign. It is most probable that we owe this change to the suggestion of the commissioners; for they say, "We beg leave to invite the attention of the Government to the advan tage and facility of establishing in this country a decimal system of coinage. In our opinion, no single change which it is in the power of a Government to effect in our monetary system, would be felt by all classes as equally beneficial with this, when the temporary inconveniences attending the change had passed away.* The facility consists in the ease of interposing between the sovereign (or pound) and the shilling a new coin equivalent to two shillings (to be called by a distinctive name), of considering the farthing (which now passes as theth part of a pound) as the 1th part of that unit; of establishing a coin of equal value to the 1 th part of the pound; and of circulating, besides these principal members of a decimal coinage, other coins of values bearing a simple relation to them, including coins of the same value as the present shilling and sixpence. No circumstance whatever would contribute sc much to the introduction of the decimal scale in weights and measures, in those respects in which it is really useful, as the establishment of a decimal coinage."

1000

100

If the recommendations made in the preceding extract, which, as we have seen are partially adopted in the introduction of the florin into our currency, we should have some of the strangest anomalies to contend with that ever yet attended a change in our moneys, weights and messures. The coin answering to the hundredth part of a pound would be in value 2 d. that is, two-pence and two-fifths of a penny. Now, supposing that this coin, which of course would be one-tenth of a florin, were introduced, and called, in imitation of the French, the Deciflorin, not one person in a thousand would know its real value, although we have just stated it correctly above; and most people would be dreadfully puzzled and annoyed to get at the real value of any number of these new coins. The following table will show the labour of conversion from the one scale to the other, and the consequent difficulties which the public should have to contend with.

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STERLING MONEY

English or sterling money means the "

Money of Accounts.

money current with

2 Farthings (d) make 1 Halfpenny, marked d. 4 Farthings 12 Pence 20 Shillings

1 Penny

1d.

1 Shilling

1s.

1 Pound

£1.

Current Money.

The next difficulty would be the material of which this coin should be made; if it were made of copper, each deciflorin would be rather more than double the weight of a penny, and a given number of deciflorins, would, of course, weigh more than double the merchants" of Great Britain and Ireland. that number of pence in the pocket. This would not answer our fine ladies and gentlemen, who love pence, although they affect to despise the trouble of carrying them. Again, if it were made of silver, it would be nearly one-third smaller than our present threepenny pieces, and would accordingly become a most unhandy coin, slipping through the fingers, disappearing through small holes in the pocket, and when dropped, lost, from its smallness of size, in the twinkling of an eye. Silver two-penny pieces, and even one-penny pieces have been coined, but only as matters of curiosity; and these deciflorins would become the same, inasmuch as the people would prefer the old pence to which they had been accustomed, or fall upon some substitute to avoid the inconvenience of the government money. Moreover, after all the attempts to introduce a decimal coinage the public would grumble until they got the binary system introduced in some shape or the other; so that we should have double deciflorins, quadruple deciflorins, octuple deciflorins, &c. as well as half deciflorins, quarter deciflorins, and half-quarter deciflorins; the values of these would be as follows:

The commissioners also propose to reckon every farthing the tenth part of a deciflorin, which, in imitation of the French, might be called a centiflorin. By this scheme, forty-farthings, or ten-pence, would be lost by the government, or by the holders of the old coin, on every pound; that is, four-farthings, or one, penny, on every florin. The blunders, mistakes and complaints which this equalization of the coin would occasion look small upon paper, but it would be found to be large in practice; and could only be adjusted by calling in the old coinage and issuing a new one, giving the holders of the old full value in the new for their money. In issuing this new farthing coinage there would require to be some coins also adapted to the binary system; for instance, we should require, double centiflorins, quadruple centiflorins, and octuple centiflorins; the values of these would be as follows:

We need hardly make any additional observations on the very awkward and untoward circumstances in which the new coinage would thus place the country.

In commenting upon the subject of the decimal scale, our pupils will find that the remarks we have made are not uncalled for, when they read the following admissions made by the commissioners themselves: "With regard to the decimal system in general, we think it undesirable to enforce it exclusively on all parts of the various scales of weight and measure even were the attempt likely to be attended with fewer difficulties than would be experienced in this country. In our opinion, the scale of binary subdivision is well adapted to the small retail transactions which seldom become the subject of written accounts, and which constitute a large part of the daily transactions in every country."

Before proceeding farther with our observations on the proposed changes in our Coins, Weights and Measures, we shall now lay before our readers a popular view of their actual state at present, with some practical notes on their past state, for the pur ses of comparison.