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MIRROR OF SCIENCE AND ART.

FRIDAY, AUGUST 19, 1870.

SATURN.

By A Fellow Of The Royal Astronomical

Society.

THERE can, we think, be very little question that amid all the wonders of the Solar System, the most wonderful in aspect, as in physical structure, is the planet whose name heads this article. In fact, we believe that no one ever contemplated Saturn for the first time in n. telescope of adequate power without an exclamation of surprise at the extraordinary spectacle presented by a huge globe, suspended in space, helted like Jupiter, and surrounded by au (apparently) dense and solid ring or rings of light. We have purposely deferred any reference to this planet until his arrival at a position in the heavens which would enable the student to follow our description by a direct reference to the object described. Now, however, that he rises between five and six in the afternoon, is on the meridian between nine and ten, and sets an hour or two after midnight, we propose to give the same amount and description of detail with reference to him that we have previously done with regard to other visible planets; and wo will say frankly, in limine, that it will be whblly our own fault, and not that of our subject, should this paper prove an uninteresting one. Premising, then, that Saturn has an equatorial diameter of 72,250 miles; that in addition to his rings eight moons circulate about him; and that he is situated at a mean distance of 874,321,000 miles from the sun, around which he performs one revolution in 1075921971 days (or something like 29J of our years), we proceed to the more immediate subject of our paper, the revelations made by the telescope as to the structure and condition of this most marvellous object.

Passing over the connection of the Assyrian god Nisroch with the planet Saturn, and the altogether extraordinary circumstance that in many of the Assyrian sculptures this god is represented as surrounded by a ring, we may pretty confidently assert that Galileo was the first observer to whose gaze anything of the remarkable appendage of Saturn was revealed. It was in the year 1610 when ho first seems to have made a telescopic examination of the planet. He employed, as is very well known, an instrument of a form invented by himself, and called even to this day the Galilean telescope, consisting merely of two lenses mounted in a tube—a convex one for the object glass and a concave one for the eyeglass. Turning this affair, which magnified, however, more than thirty times, upon Saturn, he was surprised to observe that it appeared triple; presenting to his eye the effect of a central globe with two smaller companions in contact with it. Two years afterwards, from a cause presently to be explained, the ring became invisible altogether, and Galileo saw the planet perfectly round. This so utterly puzzled him that he would appear to have persuaded himself that either his instrument, or, as he says, "some demon" had deceived him in his original observations; and, in seeming disgust, to have ceased to regard this particular planet at all. Whether it be so or not, one thing is quite certain, and that is, that Galileo makes no allusion of any Bort to Saturn subsequently to the year 1612. Between forty and fifty years afterwards wo find Hevelius observing Saturn with great attention. He seems to have got very little further than Galileo, either in what ho conld see or in his interpretation of it; at least, he finally came to the conclusion that the globe of the planet had two lunules or crescents of hyperbolic curvature, attached by their cusps to its body, the dark sky showing between the inner edges of these crescento and the ball of Saturn. He fancied that a movement of rotation sometimes carried one of theBe lunules in front of the planet's disc and the other behind it, and so imagined that he had explained the round phase which had proved so great a stumbling-block to Galileo. It was, however, Christian Huyghens, who, in 1659, first satisfactorily solved the mystery of the planet's aspect in his "Systema

Saturnium," in which he showed how the appearances he had observed were produced by a thin flat ring surrounding Saturn's globe, and situated in the plane of his equator. On the night of the 13th October, 1665, Dr. Ball, and his brother, Mr. William Ball, of Minehcad, in Devonshire, detected that this ring was divided into two by a black line, which has since been known as " Ball's division." This was rediscovered by CaBsini, in 1675. It is worthy of notice that William Ball must have been a very assiduous observer of Saturn, as we have it on the authority of Huyghens that he saw the bands or belts upon the body as early as 1656. Iif 1662, Auzout seems to have seen the shadow of the planet upon the ring. Other discoveries we shall advert to in describing the various appearances presented by Saturn when viewed with the optical aid now at the command of astronomers.

We have referred to the appearance aud disappearance of the ring (or rings) above; and it will perhaps make our subsequent observations rather more intelligible, if, prior to entering into a description of the physical features of Saturn revealed by the telescope, we try to give some notion of the reason of this, and of the very varying aspect of the rings themselves, presented at different epochs. Reference to the annexed figure will assist our explanation.

[graphic]
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In it, let S be the sun, the inner small ellipse be a perspective view of the orbit of the earth, and the outer large one of that of Saturn. Then, if for simplicity, we imagine these orbits to be in one plane, aud remember that the axis of Saturn, like that of our earth, always travels thiough space (practically) parallel to a fixed line, we shall see that when Saturn is at A—the earth being (say) at E—we shall see tho upper sido of the ring and the north pole of Saturn—a condition of things which obtains at this moment. It will be equally evident that when, after an interval of some fifteen years, the planet arrives at C, his south pole and the under side of the ring will be seen. In both these cases it is pretty obvious that the ring will appear as a broad ellipse—in fact, at the time of greatest opening, the minor axis is about half tho length of the major. A little study of the figure will show that, as the planet travels from A towards C, and from C towards A, the ring will gradually close up, as we shall be looking at it more and more edgeways; and that at intermediate points, such as B and D, we should (with a sufficiently powerful telescope, and the plane of the ring passing that of the sun) see only the illuminated edgo of the ring as an excessively narrow hair-like lino of light. It will also be noticed that when the plane of tho ring passeB through the earth, or when the sun is shining on the side turned away from us, the ring, save on a narrow dark line crossing the planet's equator, will utterly disappear. Furthermore, when we reflect how very slowly, relatively speaking, Saturn crawls along in his orbit, it will be easily perceived that our earth may—and, as a matter of fact, does—paBS twice through the plane of the ring before it passes the plane of the ecliptic, so that ordinarily tho ring disappears twice when it is in its ascending and descending nodes. Under the circumstances of such disappearance the effect presented is that seen below—

[graphic]

which is a facsimile of a drawing copied from our Observatory book, under the date of January 25, 1862, and represents the planet at 12h. G.M.T., as viewed in a 1»in. achromatic, with a power of 250. As an illustration of the return of the ring to visibility, we further append

rently a detached part of tho ring, was in reality a satellite. We may add that the ring disappeared again in the May following of the year in which these drawings were executed.

Assuming then that tho Btudent has acquired a clear conception of the reason why this remarkable appendage varies in appearance from a wide ellipse to a straight line, and ultimately disappears only to follow its cycle of changes in a reverse order, we may resume the thread of our description of the discoveries which have been made with regard to the structures of Saturn generally.

Reverting then to the duplicate character of the ring, it will be remembered that it was known to be double as early as 1665, aud it is somewhat to the credit of Cassini (when we consider the nature of the optical means at his disposal) that he, ton years later, not only saw the division, but detected the difference of tint between the outer and the inner ring, the inner one being the brighter of the two. He compares this difference to that exhibited by burnished and tarnished silver. The next observation of any importance which we meet with in chronological order, is that of Short, the famous optician and reflector maker, who about the year 1760 would seem to have detected a division, or rather divisions, in the outer ring itself. In the month of December, 1823, M. Quetelet was trying a telescope by Cauchoix, in Paris, and thought ho saw the outer ring to be double. On December 17, 1825, Captain Kater, employing a Newtonian reflector, by Watson, of 6in. aperture, saw three black streaks, the middle one being the strongest upon the outer ring. One friend with him could perceive several; another one only two. During the following January Kater repeated these observations with a Dollond telescope of the same construction, with which, under equally favourable circumstanoes, he could sometimes see the lines and sometimes not. He hence inferred that the divisions, whatever they might be, were not prmanent. Since then this division of the rings has been seen by a considerable number of observers, including Encke, Padre de Vico, Lassell, Dawes, and many of less eminence. It may encourago incipient telescopists if we mention that during the year 1858 and part of 1859, we ourselves on several occasions saw this division fairly enough with the same instrument and power that we have employed in making the delineations of the planet which illustrate this paper. It was never equally visible on both sides simultaneously, though Sir William Hcrschel noticed that the inner ring became shaded off towardB the interior edge; and the late Rev. W. R. Dawes, on a night of exceptionally fine definition, in the year 1851, saw this appearance resolved into a set of very narrow concentrio bands, getting darker and darker as they approached the inner edge of the ring. He compared the appearance to that of steps leading down to the dark interval between the ring and the ball. In connection with the two principal bright rings of which we have been speaking, we may call attention to the remarkable fact, that if it be permissible to compare the measures (or estimations) of Huyghens with those of Sir William Herschel, and these again with the refined and accurate ones of the great Russian astronomer, Struve, there can be no possible doubt that a most extraordinary increase has taken place in the breadth of the system within the last 200 years, and that the inner edge of the ring is rapidly and perceptibly encroaching on the space by which it is now separated from the body of the planet. In fact, should this contraction go on at its present estimated rate, it has been calculated that by the year 1980 the dark ring of which we are immediately about to speak will be in actual contact with Saturn himself.

This interior dark ring, to which we have just referred, appears of a purple, or rather slateco'.oured tint; it has been discovered within the last twenty years. Wo say " discovered," albeit there are plenty of indications that it, or at all events a part of it, must have been seen without its nature being detected a very long time since. The first record we have of it as an unmistakable appearance is that of the lute lamented American .Professor Bond, who observing at Cambridge, in the United States, on the night of November 11, 1850, with the gigantic refractor of l-t-921n. aperture, then remarked that the inner edge of the inner ring seemed to hnve n, kind of nebulous margin crossing the ball of the planet as a narrow belt. The actual shadow of the ring j itself on the ball was seen below the ring. In j total ignorance of what had been observed iu America, the late Rev. W. R. Dawes. F.R.8., ontfie night of November 25th hi the srraro yenr, while regarding Saturn with an achromatic of 6-4in. diameter, was struck with a similar appearance. He repeated the observation on the 'iyth of the came month, and again, in conjunction with the present President of the Royal Astronomical Society, Mr. W. Lassell, F.K.S., on December 3rd, ou which night they both satisfied themselves of its existence. Oddly enough, news arrived on the very next day, December 4th, of its discovery m the United States by Mr. Bond. It may be somewhat instructive to add, as showing the imperative necessity which exists fur recording any new or abnormal appearance, that in the year IS'28 this ring must undoubtedly have been seen iu a G Jin. Cauekoix achromatic, in the observatory (it Home; but that nobody seems to hnve made any note of it, nor, in fact, to have troubled his head about it. It was, however, perceived by Dr. Galle, at Berlin, teu years later; though what has become of his observations, or rather of their rvcord, wc are wholly ignorant. Assuredly, su far as Bond and Dawes were concerned, the discuvery was quite original. By far the most remarkable thing in connection with this obscure ring, however, is that—to say nothing of that painstaking old observer, SchriHer, who expressly speaks of the space on each side of the bull being as dark, or darker, than the surrounding sky— neither Sir William nor Sir John Hcrschel, who zealously observed Saturn, nor Struve, who measured the whole of the dimensions of the planet and his appendages over and over again with the great 9-bin. Dorpat refractor, ever seem to have had the least suspicion of its existence; while, since 1850, it has been seen in one of Dallmeycr's 3 Jin. achromatic, and is unmistakable in any decent telescope of 4in. or upwards iu aperture. It seems difficult to escape the inference that this strange object must have increased most remarkably in brightness within the last thirty years. Dawes, and after him Otto Struve, thought that the dark ring was itself divided into two; but this suspicion has not been confirmed, uor is it quite certain that there is a visible division between it and the inner bright riug. Before dismissing this part of our subject we may say that astronomers ordinarily designate the three rings, commencing with the outer one, as A, B, and C—B being, of course, the broader (and inner) bright ring, and C the crape ring.

(To be concluded next week.)

INORGANIC CHEMISTRY.

By George E. Davis,
Honours Certilloutod Teacher.

(introduction.

CHEMISTRY, or as it was first termed, alchemy, is a science which we may trace from remote antiquity; and, indeed, its course is more distinctly traced throughout the earlier ages by the fact that the alchemists were supposed to practise what was termed the "black art," and were, in general, supposed to be in league with demons.

In the pictures we have presented to us of these alchemists, their workshops seem to bear a mystic air; the alchemists themselves look grave and dull; whilBt the bottles which are ranged upon the shelves are covered with symbols which add more and more to the mystification of the scene. These alchemists worked with salt and mercury, their aim being to produce some hypothetical compound, or to form by some yet unmade mixture the philosopher's stone. Thus alchemy went on: fortunes were dissipated and money spent upon experiments which, although set down by some as utterly worthless. often turned out successful in a different point of view: mixtures were made—they were heated, distilled, cooled, or brought into a state ol

solution by means of one or other of the several acids or solvents then known, and the result was not what was originally expected but some new compound, which was iinincdiately designated by some fanciful name at the optiou of the discoverer.

In this manner several valuable products were discovered which added greatly to the advancement of the science. I may oite, as an instance, the discovery of vitriolic acid, made at the close of tlie loth century by Basil Valentine, a monk of the Erfurt monastery.

These illustrations wil': serve to show that alchemy was that science which had for its object the formation of those substances which are now considered as having no existence. The mercurial earth of Becker, and the phlogiston of Stahl, which were then looked upon as separate entities, have now been distinctly proved erroneous theories—theories which showed an admirable amount of ingenuity in their construction, bnt which held no way against truth.

Instead of trying to make gold and the philosopher s stone, modern chemistry pursues its course iu a different direction: it has for its object the study of those elements or particles of matter which come immediately under its notice—their properties and their combinations with one another. The chemist works, not as formerly, to isolate or determine the properties of phlogiston and other analogous bodies, but experiments with a view of classification, reducing his experiments to laws which may serve for the guidance of future generations.

A series ou inorganic chemistry will not require much introduction to the readers of the English Mechanic. Since the journal first made its appearance ample provision has been made in its columns for notes and queries in the above science; many valuable letters have appeared, and extracts have been made from the various scientific periodicals whenever they have afforded articles likely to be of general interest.

The readers of the English Mechanic have had a series on "Modern Chemical Notation;" symbols have also been thoroughly explained (pp. i'J and !)7, Vol. XI.); and as the chemical student should know the elementary facts about light and heat, magnetism and electricity, he cannot do better than follow " Sigma" through his course on electricity.

The present series, which these few remarks arc intended to introduce, will be made of a thoroughly practical nature. Chemical technology will be studied in most of its branches—in all those at least which bear upon the subjects of the series; analysis, qualitative and quantitative, (the latter branch will be subdivided into volumetric and gravimetric), will be treated on; and also the blowpipe reactions of the various metals and elements will be inserted in their respective places.

Chapter I.

Chemistry is the science which treats of matter in its many forms; its decomposition into those bodies which an1 termed elements, and also of atoms; the probable ultimate particles of the elements as we know them, or as they have at present been studied: it treats of their properties and their combinations with one another, whereby we are able to form them into groups, the members of which exhibit a strong family likeness.

Chemistry is truly an experimental science; the laws which govern it are the result of exact and laborious experiments performed by those men who have devoted a whole life to its study. It is not to be looked upon as an isolated science, but a branch of -one great whole—natural philosophy. The student may begin with chemistry, but he will soon find need of a good general knowledge of the cognate sciences—light, heat, magnetism, and electricity.

Matter, or the bulk of the material world, is at present known to consist of 64 element), or (>4 forms of matter which have not been proved compounds by the most powerful re-agents, or by the most powerful forces which have been brought to bear upou them. The elements are, then, of necessity, timplc matter, whilst matter containing several elements is designated compound.

Matter presents itself to our notice in three forms or physical modiiications—solid, liquid, and gaseous—which, however, are often not permanent, but dependent upon the forces by which they are influenced. As au instance of the first physical form we may take ice. The molecules iu this form keep their relative positiou unless acted upon by an external force—such as

that of heat; this latter force being kept »«ia piece of ice tends to retain the form gr.va ■ by nature or the hand of man.

In the liquid state, such as may be illn«fx by water, the molecules have a tendency t«ii over each other; in fact, they have no perou position, and by the application of heat U.,transformed into the third physical for* gaseous state. By the application of ba water this force overcomes the cohesioE c particles, and also the force of adhesion :■? • vessel in which it is contained. The roe. steam, and the only visible manifest*Lion v, vof its presence is its condensation, dsearr < comes in contact with the atmospheres^? is itself an invisible gas.

The specimen given above of tb< or throngh the three states is not confxaeit s pounds; by the application of intense 15.1* enry. winch is a rlrnU at ordinary tetrocci becomes sohd (at - S9"4° C), andbytk>>.~ tion of heat it is converted into vapour. »r boils at 3501 C, and emits a colorrriw — on'> hundred times heavier than hydro-re

Elements, Atoms, And Molecules.Jito seen that ordinary matter is not capatu ■» tuitions subdivision; for taking water 1 Lample, the theoretical division etops *v reach a molecule. A molecule of the rjor . smallest group which can take part in ir inical action. But. although we hare rem limit of divisibility ns regards water, we r;: split up that water—thotmolecnle of wat.rsimpler matter; its constituents, orrgen s hydrogen. By the action of the voltaic banr upon acidulated water it is decomposed, mtin two gases named above. These gases hnve Ksnbmitted to the most energetic forces known v the chemist, but without success ; at least, in tte direction to prove their compound constitution.

We have then divided water and formed* molt cule; this molecule or smallest portion of wntct which could exist b s free state has been further subdivided, and at last ws have reached the ultimate atom. The existence of atoms has oitec been spoken of ambiguously, and as having rel» tion to chemistry alone; but such ideas «rr totally erroneous. If we believe in the combrs tion in multiple proportion we must support lb fact by the atomic theory. And, again, wr iw no chemistry to support the hypothesis—k electricity, and the cognate sciences affrra -5 cient proof of its truth.

Radicles.—The elements, or sircat *' unite with each other to form composes- *so doing they exhibit certain (legs* "ffe?cach clement in its uncombined B& £ *oc tially a simple radicle, having variosi*-*" force. A group of elements not beia *ta?i but possessing chemical force, is calis 1 ■"*" pound radicle; instances arc to be t"x carbonyl C O' and sulphuryl S 02" ; they***' as elements, replacing them in many a* compounds. (See also page 98, Vol. XI)

Then, again, the elements may be divfe-i"' two great classes—chlorous (elcctro-nefsc* and basylous (electro-positive). When a» pounds are decomposed by the voltaic banc" some (chlorous) make their nppeaj-anee U' positive pole, while the basylous appear «.'"• negative. The most stable compounds are t<*tr by union of dissimilar elements, whilst *!£-" combinations are characterized by the ir rats*nature ; potassium (basylous) unites with x energy with chlorous oxygen, and the resui-. very stable compound; but when chlorine ■ nitrogen enter into combination, these" ehlorons elements are so loosely united that resulting compound cannot safely be touched *"out danger of causing a fearful explosion.

Symbols, Nomenclature And FoBsitn_t.the reader will turn.to pp. 49, 97, he will £.<>. • a recapitulation on this heading is quite Tjmhi sary. The circles will be omitted in grit formula? for the future.

Atomic And Molecular Weights.—A litr. hydrogen weighs 0-0396 gramme, which we has been denominated a crith; a litre ol 0x5 weighs 1-4348 grammes—that is, Ultimo* lira than hydrogen, or 10 critlu. Now, as » volumes of the simple gases (with a few ex tions) under the same pressure aud tempera contain an equal number of atoms, the a tor oxygen must be 1C times heavier than ths hydrogon.

But the reader will probably say, How Sltb atomic weights of those elements dete-rrxii which, like carbon, have never been r-erirl gaseous? It has been found by experiment 35-5 parts of chlorine unite with 1 of hydra and as 108 parts of silver unite with 85'5 of chlorine, 108 must be the weight of silver. For the determination of the atomic weight of carbon, diamond was burnt in a stream of oxygen; and from the experiments of Dumas, Erdmann, Liebig, and many others, the atomic weight of 12 has been adopted. If the metal be a dyad, the atomic weight is that quantity which unites with 16 parts of oxygen—calcium, for instance— the atomic weight being 40. This refers only to the normal oxides; the higher acid or basic oxides are of course exceptions. The molecular weight is dependent upon the molecular volume, which volume is that which is occupied by two atoms of hydrogen at the same temperature and pressure. The molecules of the monad and triad elements contain two atoms, with some of the pentads—therefore the molecular is twice that of the atomio weight. Most of the artiad elements have a molecular weight which is identical with tho atomic ; one atom, as in the case of mercury, occupying the same space as two of hydrogen. The molecule of phosphorus vapour occupies half the space of a molecule of hydrogen, if we tako two atoms to equal a molecnle; but in the above a litro weighs 62 criths, or 12-1 as the molecule weight, and as other experiments give 81 as the atomic weight, the molecule must enclose four such atoms and remain the normal size. Arsenic resembles phosphorus in this respect.

The molecular weight of compounds may be found by adding together the atomic weights of the constituent elements, and if the density is required the molecular weight must bo divided by the molecular volume; nitric oxide (Na 02) has a molecular weight of 60, but a density of 16, the volume being 4. As the elements unite with each other in definite parts by weights they also combine by definite volumes or parts by measure; two volumes of hydrogen unite with ono of oxygen to fpnn water; equal volumes of hydrogen and chlorine unite to form hydrogen chloride ; whilst ammonia gas is composed of threo volumes of hydrogen and one of nitrogen.

Acids, Bases, And Salts.—Acids are generally formed by tho action of water upon the higher oxides; both are decomposed, and a new compound results, in which the atoms are very differently arranged. The characteristic of the acids proper is tho ease with which they exchange their hydrogen for another basyl. By the action of one moleculo of water upon an oxide molecule, either one or two acid molecules may be formed; when the latter takes place the acid is what is termed monobasic, that is, contains only one atom of hydrogen replaceable by metals. If, as in the former case, only one molecule of acid is formed by the mutual decomposition of tho water and chlorous oxide, a dibasic acid is the result; an acid which contains two hydroxyl radicles, or two atoms of (iisplaceable hydrogen.

(To be continued.)

BEOENT IMPBOVEMENTS IN THE
MANUFACTUBE OF GAS.

THE manufacture of gas is a subject of more than passing interest to many of our readers, and in giving the opinions of those best capable of deciding on the utility of the various suggested improvem»nts, we ask the attention of those of our subscribers more particularly interested in the matter.

For some time past numerous gas engineers have been engaged in endeavours to convert the valuable fluids contained in tar into permanent gases. These attempts to utilize the rich hydrocarbons of the tar, however, have hitherto not been Bo successful as might be desired, principally on account of the naphthaline and solid deposits creating obstruction in the mains and pipes, and carbon in the retorts, without the anticipated increased quantity of gas. An improvement has, however, been introduced at Cork, by Messrs. Hill St Lane, which bids fair to overcome these obstacles. Their process, which is patented, consists in the thorough amalgamation of the tar, with a portion of the coal to be carbonized. From 30 to 40 gallons of tar are mixed and ground up with three qnartcrs of a ton of coal and a quarter ton of breeze. The proportion used is 25 per cent, of the total quantity of coal to be carbonized. The advantages claimed for the process are a larger yield of gas, increased illuminating power, and the re-conversion of the breeze into coke, its particles being cemented together by the pitch of the tar. It is said that

inferior Welsh coal, treated under thispatent, can be made to yield 15-candle gas. The rationale of the process appears to be that, whilst in the former experiments the tar was merely distilled, in this it is in great measure decomposed, and the poorer gases coming from the coal combine, while in their nascent state, with the hydrocarbons of the tar, which are converted into permanent gases, instead of condensing and forming obstructions in the apparatus.

Of all the machinery in general use upon gas works, probably no portion is so uncertain and so unsatisfactory in its operation as that of the ordinary coke " scrubber." In order to extract the tar, the gas after leaving the condenser, was passed through vessels filled with coke or breeze. The transition from these breeze-boxes or tarfilters to " scrubbers " was accomplished merely by increasing the depth, and allowing water to trickle through; but only a small quantity of water being required, the difficulty was to distribute it equally. To meet this, Mr. Hill adapted the well-known " Barkers mill" to the purpose; but even this ingenious contrivance was not sufficient of itself; it distributed the water equally, but the quantity required to keep it going made the resulting liquor too weak to be profitable. Mr. Hills then introduced a " tumbler," a sort of double trough with a division across the centre, and so balanced over an open box that the small stream of water alternately fills first one division and then the other, the division into which the water runs remaining in position until it is filled, when it, so to speak, tumbles over, emptying its contents into the box, thus affording sufficient water to canBe the mill to turn for a minute or two, but which stops when the supply is exhausted. Neither the Barker's mill, simple, nor the " tumbler " proved successful, and both have since been discarded. The most common method of filling scrubbers at the present time is with coke; and these seem to answer very fairly provided the gas is free from tar. However, the invention of Mr. Livesey is a decided improvement, and will, in all probability, be universally adopted. It consists in fitting tho interior of the scrubber with a number of thin boards, disposed so as to present an enormous surface of liquor to the passing gas. In a scrubber 15ft. 6in. diameter by 28ft. high, are placed 22 tiers of boards about i-in. thick; and as there are 258 boards in a tier the whole surface is about 128,000 square feet. A layer of coarso cocoa-nut matting is placed on the top to spread the water. The gas is passed through these scrubbers, the first two being plentifully supplied with liquor, and the third with a small quantity of water. The greater part of the ammonia is Absorbed by the liquor, which is increased in strength to lOoz. or lloz.; the remainder is removed in the la6t scrubber by the use of from 5 gallons to 6 gallons of water to the ton of coal, or scarcely more than half a gallon to 1,000ft. of gas. The liquor so produced is of from 7oz. to 9oz. strength, while the same vessel filled with coke would require 3 gallons to 4 gallons more water to the ton, and would only produce liquor of 3oz. to 5oz. strength; therefore the arrangement of thin boards is about twice as profitable as the use of the ordinary coke scrubber.

In the matter of burners, Sugg's "steatite" and the slit fish-tail are recommended as preferable to the two-hole fishtail. The Brbnner burner (a kind of split batswing) is reported as giving an illuminating power of 12 candles, with an hourly consumption of oft. Indeed, the batswing burner has beaten the ordinary fishtail completely out of the field, as it gives a much better light with about the Bame consumption of the gas.

Some method of completely removing the sulphur from the gas is still wanted, as although its amoimt has been reduced to a minimum, there is yet sufficient to make its presence felt.

SCIENCE FOB THE YOUNG.*

By The Bev. E. Kernan, Clongowes College.

Application X.

Inclined Plane.

{Continued from page 485.)

WEBE the thread of the nut cut away all to a small part, and the nut-block still kept in position, the working of the screw would be

* All rights reserved.

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clear the elements of a screw. Standing on tho base A is shown one turn, s s, of a screw. The flat strip of metal, a a a1, wound in a spiral, is the thread of the screw. The cylinder on which a a a' should be rolled is omitted, and in its place a perpendicular plate, b «, supports the spiral. The upright B has two projecting pieces, in which slides the bar C, the lower end of which rests Cby a small wheel) on the screw spiral. This bar O represents one portion of the nut, movable perpendicularly. The screw spiral a a a' can move horizontally, being joined to the disc D, which has a pivot p, and lies upon small rollers in the base. A cord e c in the groove of the disc, and fastened at some one point of it, is a convenient means of moving the screw spiral. Lastly, a sheet of paper (No. 2) is cut of the same size and shape as the support b b, and wrapped round the support. Now, to remove all doubt of the spiral a a a' being an inclined plane, it is only necessary to unroll the spiral or its support. The paper sheet being an exact model of the support, is taken off, and when drawn out straight shows an unmistakable inclined plane, which has suffered no change by being rolled height to point. To show the action of the screw upon the nut, turn the disc D in the direction of the arrow. The bar C is forced up. Here is seen by the effect on one bit, what is the effect on the u>lu>le nut. Turn the disc in the opposite direction, gravitation forces the bar (the nut) down, and thus besides showing a common action of the screw, represents what would occur if the bar were subject to the pressure of the under side of the screw. The bar would be drawn down apparently, but the real effect would be the forcing under of an inclined plane having a (not a) for pi int; in fact, the reverse of what is seen in the figure, in which a' is the point of the plane.

This apparatus so far only shows one motion of screw (horizontal) and nut (perpendicular). But it is easy to imagine modifications, by which all the motions of both screw and nut could be represented. It would be too long to enter into these modifications, and the necessary minutiie of detail in describing by diagram might produce confusion in the mind regarding this point (action of the machine), already perhaps too much extended.

III. Conditions of equilibrium. They are to be found in the 4th case of the inclined plane

P H

— = —; for in the screw the power is always

applied horizontal to the base of the inclined plane which composes the screw. In the screw the "height" (H) is represented by the pitch or distanco (d) between any two threads; and the " base " is replaced by the circumference 2 w r; the formula then becomes 8hould the divisor

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it is the mathematical expression of any circumference; r is the radius, and 2 ?r tho relation of the diameter to the circumference, which not being an exact whole number is rendered by the decimal

3-141696 From the formula can now be

drawn all the conditions of better action, i.e., how P may be as small as possible. It is therefore evident—1st, that the smaller d is the bettergame principle as in the inclined plane; the less the height, the less is P. Hence the closer the threads the more power is gained. 2nd. The greater the radius of the oylinder r, the better —same again as in the plane—the longer Ac. Hence the larger the body of the screw the better, the pitch remaining the same. 3rd. No gain if (r) be increased in such a way that (d) is proportionally greater. The reason is evident—the angle of the plane remains unchanged. 4th. What is gained by the reduction of d is lost in the motion produced. Before tho change at each turn, the body could be moved a distance = d; after the change it will (it can) only be moved = d - n. Practically, therefore, time is loBt in effecting the same work. 5th. What is gained by increase of r is lost in accomplishing the same perpendicular work. Recall the principle of " virtual velocities."

N.B.—In practical use, the power is always applied to the screw by means of a handle of some Wnd. The principles of this handle not having "^^^TBeTTSs yet studied, it (the handle) cannot here be made enter into the formula of the screw; but it is necessary to remark that it may be found in books as represented by the letter r of the expression Ire r. For the present, it is enough to know that the change of r mtust make a change in the value of P, when r in 2 re r stands for the handle with which the screw is to be worked. This consequence, therefore, in no way clashes with the conclusions 2nd and 3rd from the formula where T is the radius of the cylinder (the body) of the screw.

IV. The uses of the screw, many though they aro, can be all included under one head, " the exertion of power (force) of any degree from the smallest to the greatest which the strength of materials will allow." This extraordinary range is in great part effected by the "pitch" of the screw, which can be reduced indefinitely as long as the form of the thread can be maintained uninjured. The applications of the screw are all interesting, and many very important.

Screw App. I.—Weight Reaction.—In general use the "pitch " is so small that the weight (the force to bo overcome) cannot react on the screw when the "power" is withdrawn. Thus, a heavy weight W, Fig. 88, lifted by a screw, cannot push

Now, as the difference may be made indefinitely small, a "working pitch" indefinitely fine can be produced. Great power is gained, but at the expense of time, in consequence of the diminution of space. There are instruments in which the contracting of the space is a gain, as it will be seen in the next application.

Screw App. III.—The Micrometer Screw.— In many optical and astronomical instruments it is necesBary to estimate division of space much smaller than those of the most delicate vernier. For this purpose is used the "micrometer screw." The essentials of this instrument are (the frame, nuts, support of r, Ac., are left out of the figure), a screw of very small "pitch," A (Fig. 90), and a circular plate B, very delicately divined. The plate is usually joined to the screw-shaft, and as it is moved round, passes under a graduated index r, which points to the number of divisions gone past, and, by its own graduation, indicates the number of turns which the screw has made. For measurement, it is only necessary to know the "pitch" of the screw; the plate will indicate the fractions of that pitch. Suppose then, the " pitch" to be 1 mm., and the plate large enough to be divided into 500 parts. Each turn of the screw moves the body, whatever it may be, to a distance of one mm.; each division of the plate shows l-500th mm. The number of turns gives the number of mm., and the index r points to the number of oOOths to be added. The micrometer may be made so as to show l-1000th of a mm, {To be continued.)

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the screw back, although tho power P has ceased to act. The "pitch" (tho H of the plane) is so little that the great force of W has but a small •' component" down along the thread, which "component" is more than opposed by one of the "obstacles." The detailed examination of the various forces produced by W will afford an interesting study to any one who may wish to fee fully the truth of the explanation just given.

Scbew App. II.—The Differential Screw.— After a certain point in various materials the thread canuot resist tiie pressure upon it—it breaks. There is then the limit of reducing the "pitch." To have a "working pitch" of less height, two screws of different pitch are made to work one into the other (Fig. 89), A, large screw moving as arrrow (a), B small screw moving as a'. On turning the handle P, the screw A advances as its " pitch " requires; but, in the mean time, B is drawn into A to the height of its "pitch;" the body W is only moved to a distance equal to the difference between the pitch of A and the pitch of B. This difference is the "working pitch."

MICROSCOPICAL EXAMINATION OF ROCKS AND MINERALS.'

A MICROSCOPICAL examination of rocks shows that, as a rule, the igneons rocks may be distinguished at once from all others by their structure, which is that of a more or less perfect network of minute crystals: in many cases all the minerals are well crystallized; in others there is an amorphous or glassy base in which they are enclosed; there are, however, other rocks, such as the Felstones and the more recent volcanic Phonolites some of which do not present this crystallized arrangement of their constituents; and then there are the Porphyrites, which are characterized by the presence of crystals of felspar in a compact fclspathio base. There is in fact a gradual passage from the compact Felstones to the Porphyrites; so that it appears probable that the amorphous base of all such rocks is simply the silicious magma or paste from which distinct minerals would have separated had the circumstances under which they wore formed been favourable for crystallization to have taken place. As a typical example of a widely distributed class of rocks, I will take for description the well known basaltic rock of the Rowley Hills. An examination of thin sections shows that it contains a triclinic felspar, angite, magnetic oxide of iron, a little olivine, and a few crystals of apatite. The felspar is known to belong to the triclinic system, as it exhibits the characteristic striie when examined by polarized light. Augite appears in minute black shining crystals, which appear bright brown, or occasionally green when in thin sections; it cannot be mistaken for any other mineral except hornblende, from which it is distinguished by a marked difference in the angles; it has also a clear glassy appearance, while hornblende is either distinctly fibrous in texture, or exhibits lines or cracks running parallel with the principal cleavage plane. Very frequently hornblende is green, while augite is yellowish brown, but this does not always hold good. The magnetite occurs in minute grains, or as thin lamhue, both being black and opaque. The apatite is seen in long acicular hexagonal crystals. The olivine occurs in crystals, and also in irregular grains, of a clear yellowish-green colour; it is, however, rare in this state, being nearly always altered to a dark green mineral. In addition to the above minerals, which mnst be regarded as the original constituents of the rock, there are also one or two zeolites, calcite, and a chloritic mineral, all of which are found filling cavities, and are secondary formations.

The use of the microscope is by no means a_ fined to the discriminations of minerals; with ia! assistance we may learn many fads, as U> :lmode of formation of rocks, the order in wkiekl the various minerals crystallized, and the alt,^ tions which have been frequently caused by si removal of mineral matter, and its replaenu by another of different chemical composition. 1> the Rowley rock, the minute crystals of apxc penetrate both the felspar and augite: the Wa also encloses crystals of felspar and magneir the augite crystallized therefore after the oii had been formed. The olivine contain* gait. magnetite only, and was probably the secuai crystallize.

Cases are not uncommon in which crystals iicaught up portions of the surrounding xnas «jj in the act of formation, and other facts ber very clearly the actual condition of the z». the moment of crystallization. For exam. a section of Pitchstone from Planitz, costs. crystals of felspar, the minute opaque pnm thickly scattered through the matrix are cm* together round the sides of the crysti been forced outwards as the latter iram'a size; this clearly indicates that daring '_ I tion of the crystals, the matrix was in a not not in a fluid state, for had the partidaa quite free to move, there would have be: crowding.

In a section of basalt from the Rhin- . olivine is in its usual fractured condition, «. some of the larger cracks have been filled I with the fine crystallized matrix in which (• are imbedded;— there is no crowding of particles; in this case, therefore, the olivine n not only crystallized, but fractured, before tk I consolidation of the mass. In another section d basalt the crystals of augite and olivine are somewhat rounded, and the cracks tilled np, so that they probably existed as crystals or grains before the ejection of tie iira.

One of the most important aids in the examination of rocks and minerals is afforded by polarized light. In many casts it enables us at once to discriminate between iioerent minerals, and not unfrequently affords clear evidence of change* which have taken place subsequently to the consolidation of the substance under examinatke When a thin section of a crystal is placed on tip stage of the microscope, and a beam of poluu-. light is passed through it, the beam is do}x.kr_ and generally exhibits colours due to interfsc the intensity of colour varies according t s direction in which the crystal is cut, xJ ssfquently, in examining a section of net £» various sections of any one mines! i> E»* always give tho same result; but as lb sr-"iof igneous rocks lie at all angles, it a ta=^ always easy to obtain some which, being Cm & an inclination to the optic axis, exhibit tc&xc: degrees of intensity of action; therefore maei which vary much from each other in this res£ may be easily distinguished.

A most important point to be noted is, tin; depolarizing action of a crystal is uniform >■■the whole surface of its section, if it consif.i one simple crystalline structure; when, howes: the light appears to break up into detached p&r-' each of which changes independently as — analyzer is rotated, we know that it is m • of a number of separate crystalline porti* either independent of each other, or sometiarrelated as twins.*

A knowledge of these facts enabled me detect the presence of olivine and its imorphs in the Rowley rock, as described in former paper, and also in the Geological ilmn zine, vol. vi., p. 115. A pseudomorph is a runs ral possessing a crystalline form, which doe* c belong to the substance of which it is compost it is an altered mineral, or, in other w. >r. i - t aggregate of mineral matter, which has b*» deposited simultaneously with the removal ( that which possessed the original crystal form it is easy, therefore, to see that the molecuJj arrangement of tho particles must be entirti different from that of the original crystal. Nd by the aid of polarizad light, such changes a: at once rendered apparent, and we thus posse1 the means of obtaining most important iu I..rrj tion on the metamorpliism of rockB and mineral of which ordinary light would afford no indicatit whatever.

Serpentine has hitherto been a great puzzle geologists, some having regarded it as an i trusive ignoous rock, others as of nietamorpb

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origin. As not unfrequently happens, both ore, I believe, right; for every section I have made clearly proves it to be an altered rook, and one specimen from the Vosges mountains contains numerous grains of olivine, in which the change is only partially developed.

These few foots will serve to indicate the importance of this hitherto neglected method of inquiry; for although the pseudomorphism of many minerals has been long studied, little attention has been directed to similar changes in rock masses.

"A subject of interest to the microscopical observer, and one of considerable importance to the petrologist, is the occurrence of minute fluid cavities in the minerals of igneous and meta morphic rocks; they have been detected in several minerals ejected from active volcanoes; but so far as I have observed, they are far more abundant in quartz than in any other mineral. Those who wish to examine them may do so by making a section of almost any specimen of granite; they are very numerous in the granite and schorl rocks of Cornwall, the homblondic granite of Mount Sorrel, in the syenite and gneissoid rocks of Malvern, and in the syenite of Croft Hill, and neighbouring bosses in Leicestershire. In these and similar rocks, the fluid cavities appear to be be entirely restricted to the quartz, that I have not yet detected any in the feldspar or mica; they are certainly extremely rare in these minerals, if they occur at all; this, if established, would indicate a difference in the conditions under which the minerals were formed, a point which I believe has not yet received attention.

For an account of the curious, spontaneous movements of the fluid in some of these cavities, and for other interesting matter connected with the subject, I must refer you to Mr. Sorby's paper already quoted.

During the past summer and autumn (1869) I have collected specimens of the igneous rocks of the Midland coal-fields from the following localities: — Kinlet and Shatterford, west of Kidderminster; the Clee Hills; Little Wenlock, near the Wrekin, in Shropshire; Coalville, near Bardon Hill, in Laicestershire; and Matlock, in Derbyshire.

A microscopical examination of thin sections shows that all these rocks belong to the same type; they do not in fact differ more from each other than do different specimens of any one of them. The toadstone of Derbyshire is merely an amygdaloidal variety.

The rocks of the Warwickshire coalfield differ considerably from the foregoing; they contain hornblende instead of augite, and are therefore true greenstones or diorites; they may be readily examined in the railway cutting near Nuneaton, and also a little to the west of Atherstone. All the rocks just enumerated are clearly older than the surrounding Permians, which are never penetrated by them.

Having now made upwards of four hundred sections of rocks and minerals, I am inclined to believe that the following results of microscopical examination will stand the test of further study. 1. The mineral constituents of the melaphyres and other fine-grained igneous rocks may be determined with certainty—a result which has not been attained by any other method of examination. 2. The mineral constituents of the true volcanic rocks, and those of the old melaphyres, are generally the same. 3. The old rocks have almost invariably undergone a considerable amount of alteration, and this change alone constitutes the difference now existing between them and the more recent volcanic basalts.

The basaltic lavas of the Rhine and Central France are compose 1 of a triclinic felspar, augite, magnetite, olivine, and frequently apatite, the same minerals as those constituting the old rocks above described. I have fine-grained specimens of the latter hardly distinguishable from recent basalts; and a section of Dolerite from the Puy de Barncre, in Auvergne, does not differ in any important particular from coarsegrained specimens from Rowley. It would be easy to extend the parallelism to other classes of rocks, but I will now only observe that we have here another proof of the doctrine long taught by Lyell—the uniformity and continuity of the laws of Nature.

Professor Favre, of Marseilles, has made some experiment* with compound* of hydrogen and palladium. His results point to the conclusion that hydrogen should be classed with the metallic elements.

REVIEWS.

The Disposal of Town Sewage. By R. W. Peregrine Birch, C.E. London: Spon.

THIS is a pamphlet in which the various systems in use for the disposal of the sewage of towns are examined. Although no definite conclusion as to the best means of arriving at that end is adopted, the brochure contains a short resume of the various systems at present in force, and points out in a clear manner their advantages and defects. The author was at one time inclined to favor the ABC Bystem as practised at Leamington, but since he examined the process at that town has seen reason to change his opinion. The author has visited most of the places at which attempts are made to utilize the sewage, and his conclusions are doubtless of value. But the fact remains, that no really unobjectionable method has hitherto been discovered, and we are no further advanced than we were some years back—save the negative information we have derived from the numerous experiments which have been carried out.

Building Societies and Borrowers ; or. Suggestions for the Consideration of the Royal Commission on Friendly Societies. By C. D. Aknaldo Friedlein. London : Aug. Siegle. The author of this little pamphlet clearly exposes the enormous interest that is really paid by borrowers from Building Societies under the impression that they are borrowing money at about 4 per cent. Speaking of the system of fines, which he acknowledges are the necessity to the proper working of the business of these societies, the writer says :—" Under the existing system the societies derive the greatest profit when the borrower falls into difficulties. Certainly no 'friendly' society ought to consider such on occasion a legitimate source of profit." The fact that a borrower pays as muoh interest during the last month of his term as he did when he held the whole sum, is sufficient evidence of the necessity for a revision of the rules governing Building Societies, as well as a convincing proof of the enormous interest in reality paid by the customers of these institutions.

Public School Reforms By M. A. B. London:

L. Booth. "M. A. B." has here gathered together tho numerous letters which have appeared in the press on this subject contributed either by himself or others. The subject is one of considerable importance, and deserving the attention of all interested in the education of the country. Vast sums are annually spent by our public schools; but the amount of knowledge given for them does not seem to be of such a character as might be expected.

the second, how is it proved that all germs are destroyed by the crashing and boiling? The arguments of this gentleman are so radically weak that we can afford to grant him his premises and then be free to reject his conclusions.

Biology versus Theology; or, Life on the Basis of Hylozoism considered. By Julian. Lewes: G. P. Bacon. This is what might be called a clever attack on modern theology; but there is very little of the calm reasoning of science in it. The author expresses his opinions in too dogmatic a fashion to carry much weight, and his failure to see two sides to a question is ludicrous in the extreme. In his section on "Life—how produced in the first instance," after telling us that a dung-heap "actually swarms with living animals," he goes on, " Taking a dead dog, let us pound the carcase in a mill to destroy all life which can be crushed and ground out of it mechanically. Having so done, let us boil the pulp and raise it to such a heat as will destroy not only life, but even germ-life, the life of ova and of seeds, incipient or developed. We have now utterly stamped out every germ of life in the reduced carcase which was once a dog, and to prevent the conveyance of germs by the air, let us wrap the pulp in cotton wool, which, on the testimony of Professor Tyndall, will effectually exclude all germ-life from without. Here then we have au animal Bubstance from which all life has been crushed out or boiled out, and to which no germ of life can penetrate ; what will follow? The mass will putrefy in time, and the putrefying mass will teem with larva? as before. There cannot be a doubt of it, if the oxygen of the air or water can percolate the cotton wrap." In the first place, how is it possible to wrap this pulp in cotton wool without allowing the germs floating in the air to settle on it during the operation? And in

RELATIVE MATERIAL STRENGTH OE FRANCE AND PRUSSIA.

TTTK Tablet, in an article on this subject, says:— In most of the conditions of national strength we find a parity between Germany and France. It is curious that in population the two countries are precisely equal. The North German Confederation, and its t r ust y allies, t h e South G erman States, count together about 38 millions of souls, which happens to be the exact figure of the aggregate population of France, as shown by the census of 1806. The several proportions are as follows :— The Confederation has 30 millions, Baden about a million and a half, Wurtemberg nearly 2 millions, and Bavaria something under five.

Passing from population to an estimate of economical advantages, there is as little difference between the two countries. Both are two-thirds agricultural; Germany has most ships, and foreign trade, and manufaetnres; but, as a setoff, French agriculture is most productive. Thirdly, as to revenue from taxation, the total of the Confederation is 40 millions, while that of the States is 12; in all 52 millions. The revenue of France is much larger, but then her national debt is also much larger; so that practically she has but little more than Germany available for all the purposes of her administration. The annual expenditure of both countries on their respective armies, so far as we know it, is about the same, Prussia spends between 12 and 13 millions, France a million more.

There can be little doubt that this war will be enormously expensive beyond all experience of European wars. Not so expensive, probably, as the conflict between the Federals and Confederates of America, in which a million of men were kept in the field at an outlay of 200 millions sterling per annum. The present outlay will be less; partly because by the conscription a vast saving is effected in bounties and pay as compared with the American system; and partly because the area of the campaign will probably be much narrower. Wars become, in fact, every year more costly as civilization advances. The Italian war of 1859, which lasted only six weeks, cost France at least 20 millions: Bismarck' s three weeks' campaign of 1866 cost Prussia nearly as much: the present outlay will certainly not be less lavish; so that from those figures we may estimate roughly, and quite within the mark, the probable cost of the present war.

The interesting question, of course, is (if it could be answered,) what advantage, if any, may be supposed to be possessed by eitherof the belligerents over the other 1 On the side of Prussia it may be said that she commences the war with a lighter load of national debt. Her total debt is pat down as less than one-third of that of France. Hence her borrowing power is greater. At the same time, as regards this war, the borrowing power of France may, we suppose, be regarded as practically unlimited. The advantage of a small debt is, however, felt in the lightness of taxation; and this advantage is very decidedly on the side of Prussia. The Germans are less burthened, and, therefore, comparatively at least, better able to bear additional imposts.

THE LEAF AS A WORKER.
(Concluded from page 391.)

BUT if wo regard the leaf only as a drawer of water, B lifter of earthy matter, a carrier of lightning, a gatherer of nourishing gases, a defence against zymotic diseases, we give it an inferior place—it is only a humble, common labourer. Man might invent and apply machinery to pump the water and evaporate it; he can enrich the soil, can put on his roof metallic conductors, and can escape epidemic diseases if he will breath pure air. "Ah 1 there's the rub!" for he can get pure air only as the leaf prepares it for him. Man can, in a measure, do the work of the leaf, but science has failed to demonstrate a way to do the chemical work that the leaf does.

The leaf is not a common labourer, then; for, though it deigns to do this drudgery, its great field of labour is elsewhere. It is an analytical chemist of the noblest order, and, as such, performs labour that Liebig, and Frcsenius, and Rcgnanlt attempted in vain, and such as no chemist can ever perform. Here it is that the leaf asserts its superiority as a worker—becomes a right royal labourer. Here it uses the same reagents that man is permitted to use, but with which he cannot succeed. And so the loaf looks down upon the great and learned chemist, and regards him as a bungler. Every exhaled breath of man, and of every animal on the face of the globe, is loaded with poison. The product of combustion, whether arising from the cheerful home fire, from the fire-box of the locomotive, from the furnace of

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