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used and discarded a gascngine.and now has one of Sir William Armstrong's hydraulic engines of ordinary con-traction. This looks very big and •clnmsy, anil the workmanship is not first-rate. It possesses also the additional disadvantage o! running at a very slow speed. Altogether we should hare thonght a small (nrbine preferable, and failing that, a steam eDgine with a boiler heated by gas. Of course when the lathe is being driven by a belt, the treadle crank is unhooked.

The leading screw is driven by a bright set of engine cut change wheels; and from this screw various motions are got for the other movements of ihe slide rest, which is self-acting on the longitudinal or traversing, the traverse or surfacing, the angular and the curvilinear cuts. These motions, it will be seen, are all contained in a very small space; and the neatness of contrivance indicates the possession of considerable ingenuity on the part of the designer.

The screw headstock has the base slide arrangement for setting out of centre when taper turning, and the usual pinching arrangement at the side for holding (he spindle fast, and preventing shake. The cone spindle is shown with the compound eccentric chuck on its nose. It has a large division-plate completely divided ; tangent and screw motion for slow rotation ; and another arrangement at the side for slow traversing.

The overhead apparatus is very compact and convenient. Its whole arrangement is, however so plainly shown by our illustrations, that a description is soarcely necessary.

MECHANICAL MOVEMENTS.*
(Continued from page 28.)

1A continual rotation of the pinion (ob• tamed through the irregular-shaped goar at the left, gives a variable vibrating movement to the horizontal arm, and a variable reciprocating movement to the rod, A.

2. Worm or endless screw and wormwheelUsed when steadiness or great power is required.

3. A regular vibrating movement of the curved ■lotted arm gives a variable vibration to the straight arm.

4. An illustration of the transmission of rotary motion from one shaft to another, arranged obliquely to it, by means of rolling contact

* Extracted from a compilation by Mr. II. J. Brown, Editor of the American Artisan.

MECHANICAL MOVEMENTS.

6. Represents a wheel driven by a pinion of two teeth. The pinion consists in reality of two cams, which gear with two distinct series of teeth on opposite sides of the wheel, the teeth of one scries alternating in position with those of the othor.

6. A continuous circular movement of the ratchet-wheel, produced by the vibration of the lever carrying two pawls, one of which engages the ratchet-teeth in rising and the other in falling.

7. A modification of No. 10, shown last week, by means of twa worms and worm-wheels.

8. A pin-wheel and slotted pinion, by which three changes of speed can be obtained. There are three circles of pins of equal distance on the face of the pin-wheel, and by shifting thesbtted pinion along its shaft, to bring it in contact with one or the other of the circles of pins, a continuous rotary motion of the wheel is made to produce three changes of speed of the pinion, or vice versa.

9. Represents a mode of obtaining motion from rolling contact. The teeth ore for making the motion continuous, or it would cease at the point of contact shown in tho figure. The forked catch is to guide the teeth into proper contact

10. By turning the shaft earning the curved slotted arm, a rectilinear motion of variable velocity is given to the vertical bar,

11. A continuous rotary motion of tho large wheel gives an intermittent rotary motion to the pinion-shaft. The part of the pinion shown next tho wheel is cut of the same curve as the plain portion of the circumference of the wheel, and therefore serves as a lock while the wheel makes a part of a revolution, and until the pin upon the wheel strikes the guide-piece upon the pinion, when the pinion-shaft commences another revolution.

12. What is called the " Geneva-stop," used in Swiss watches tolimit the number of revolutions in winding-up; the convex curved part a b of the wheel B serving as the stop.

18. Another kind of stop for the same purpose.

14 and 15. Other modifications of the stop, the operations of which will Le easily understood by a comparison with 12.

(To be continued.')

THE PEDESPEED.

(Illustrated on page 61.)

A FEW mornings since, says the Scientific t\. American, a quiet gentleman and a handsome youth walked into our sanctum, bringing with them a ineer-looking package. While the

elder of the two gentlemen entered into conversation with us, the younger undid the package, disclosing a pair of wheels some fourteen or fifteen inches in diameter, to which were attached some stout hickory stirrup-like appendages, in the bottoms of which were foot pieces, shaped like the woods of common skates.

On one side of the stirrup-like appendages were firmly fastened metallic plates, each having a short axle or bearing projecting from its centre, upon which the wheels above-mentioned turned. Tho stirrup-like appendages were made of flat strips of wood about three inches wide in the broadest portion, bent so that one side was nearly straight, while the other was made to meet it about midway to form a sort of loop. In the bottom of this loop were placed the foot-pieces above described, provided with toe straps and a clasp for the heel. To the upper end of the stirrups was attached a piece of wood to fit the outer and upper conformation of the calves of the legs.

In less time than it took us to note these points the young gcntleraau—who was subsequently introduced to us as tho son of the inventor of this singular device—had strapped on the wheels and commencad rapidly gliding about among chairs and tables with singular swiftness and gracefulness, A space bciDg cleared he proceeded to execute with seemingly perfect ease, the iosidc and outside roll, figure of eight, &c. &c, amply demonstrating that the "pedespeed" has all the capabilities of the skate, both in the variety and grace of the evolutions that can be performed with it.

(Jur engraving gives an excellent representation of this invention. Of course no mere carpet knight accustomed to roll about on the common parlour skate, can nse these at the first attempt. They require practice ; but when skill is once attained, there is skating the year round. Had the "pedespeed " been introduced on our rinks this winter during the long period stockholders have prayed in vain for ice, their stock would have stood higher in the market than it does at present.

The " pedespeed " is light and strong, and is capable of use on surfaces where the ordinary parlour skate vould be useless. The inventor, a large and heavy man, informs m he can nse it constantly for two hours without fatigue. For gymnasiums, colleges, and parts of tho country where no ice ever occurs, it affords a delightful, healthful, and graceful pastime at all seasons of the year.

When used by ladies, shields may be employed to cover the top of the whoels, so as to protect tho dress.

SCIENCE FOE THE YOUNG.
Semes I.—Mechanics.

Introduction.
By The Rev. E. Kehnan.

THE object of these papers is to lay out for the beginner in Mechanical and Physical science a course from which he will never require to deviate permanently, no matter to what extent circumstances may induce him iu after years to increase his scientific acquirements.

For such an elementary course, however, no great mathematical knowledge is required ; the use of simple algebraical formulas, some geometry, and the first principles of trigonometry are, as a rule, enough. Where exceptions occur the means by which full satisfaction may be obtained later on can be indicated. Moreover, in many branches of science, the gpeat principles can be acquired scientifically, and yet simply, without that mathematical learning employed for their full theoretic development by the more advanced scholar.

Mechanics being the foundation of all true knowledge, claims the first place in a scientific course. The series on mechanics may be divided into three parts. The first sets forth some necessary preliminaries, which, once determined and understood, facilitate the work to come; the second contains all that is usually understood by mechanics in its widest tense ; the third treats of bodies in a state of vibration, practically sound, acoustics, which is so closely connected with mechanics that it can be shown to be contained in the definition of this science.

Past I.—Preliminaries. Thcee may be classed under three heads: The object of mechanics, with the division of the subject; the general properties of matter; and the explanation of terms required for study.

CHAPTER I.

OBJECT OF MECHANICS; DIVISION OF THE
SUBJECT.

Before answering directly to the question, "What is mechanics 1" it would be useful, if not even to a certain extent necessary, to say what it is not. First, then, mechanics is not the method of working in wood or in iron. They who are thus occupied are called "mechanics," but they are not thereby designated as having arqnired the science of mechanics. Not but that they could possess it, and would profit much by a knowledge of its principles. Frequently their knowledge is but a mere routine of fncts, handed from one to another, the cause of which they do not understand. The small amount of mind required to obtain knowledge of this class, and the fact that such knowledge is not unfrequently combined with great mental deficiency, are the reasons why the "mechanic" is not considered as having the higher gifts of intellect. Secondly, the science of mechanics is not the dull, dry study that some imagine.

It is quite true mechanios do not possess for some the interest which, for example, the brilliant experimental part of chemistry excites. But if so it has none of the dull, plodding, mere memory work of theoretic chemistry. Every proposition.of mechanics sparkles with"proof, mathematical and experimental. With a pencil and paper the thousand phenomena which may ocour are discussed, and their cause, result of combination, &c, declared; the instruments are brought forward, and experiments prove the truth of the theory. Again, the constant occurrence within us and around us of the exemplification of mechanical principles is a new source of interest to an intelligent mind. So far what mechanics is not. Now, on the other side, mechanics is that part of natural knowledge which best deserves the name of a "science." For its principles have, of all others, been put to the severest of tests—length of time, found as they are in the very first pages of the history of science; extent of application, including, as they do, everything in the cosmic system that has as yet been brought into a really scieutific form. And so strictly is this latter true, that the fundamental principles of mechanics are every day extending themselves to new branches, rendering clear and logical what was before bnt a collection of facts, without explanation other than obscurities or contradictions. Thus from the principles of mechanics of solids

applied to tho liquid state has arisen the science of hydrostatics and hydrodynamics; from their extension to the gaseous state has resulted the science of pneumatics. Passing to the confines of the ponderable world, to the connecting link betwuen matter tangible an d untangible, sound is discovered to require no new principles. Beaching farther, to the region of what are usually termed imponderables, the principles of mechanics have seized upon light, aud made it subject to their unerring laws. By this great conquest are explained phenomena mo-t complicated and apparently contradictory, which had before been but an enigma. By it, without fear of error, it can be shown that in such and such conditions, certain extraordinary phenomena should be observed which reason would be inclined to reject as impossible or absurd; for instance—that two lights can be a cause of darkness. It is not surprising, then, to find Dr. Lloyd in his lectures on light, say of Fresnel, the French philosopher, who worked out the mechanical theory of light, that he has " reared the noblest fabric which has ever adorned the domains of physical science— Newton's system of the nniverse alone excepted." Even beyond light has mechanical investigation progressed. Heat, less tangible, is being proved, every day, more and more, to be but a " mode of motion." The time is perhaps not far off when electricity shail cease to be that unknown mysterious agent, shall yield its secret to mechanics ; showing to the wise ones to what a distance from the truth they have wandered, how they have groped in the dark, wasting their energies in theory and speculation.

What, then, is this so much lauded mechanics? It may be differently^ defined, according to the point from which it is viewed. The following definition will suit the form of the present series: Mechanics is the study of the laws which regulate the action of external forces upon all bodies. Bodies exist in some one of the three states, solid liquid or gaseous, and the student cannot begin too soon to keep this triple state of matter before his mind. That solids can be affected by forces requires no proof. For liquids it is only necessary to place a tray with water on a table ; the least stir ruffles it's surface; for gases, the rushing of the "thin air," tho winds, the storms supply superabundant proof. By the word external is to be understood some manifest action or effort at action; and this effort may be from the nature of the body itself, or from some external source. Thus is mechanical study distinguished from others in which action not direotly manifest is the chief object: for instance, chemistry. The study of the laws includes not only the mere btatcment of them, but also the proofs of their truth, and their actual or possible existence in action, iu natural or artificial combinations ; in a word, the applications of the principles contained in the laws.

{To be continued.)

A GRAND ORGAN.

ATRIAL ha9 been made of the tone of the graud organ which is being built for the Royal Albert Hall, at the works cf Mr. Willis, at Camdei;-town. This magnificient instrument is remarkable not only on account of its size and the number of its pipes, but also on account of the excellence of its design and construction. It is 65ft. wide, 70ft. high, and 40ft. deep. It weighs over 150 tons, and has nearly 10,000 pipes in it. The largest pipes are 2ft. 6in. diameter—the smallest about a couple of inches long, and not much thicker than a barley straw. In all there are some nine miles length of pipes of various sizes. There are no less than 138 stops, 20 couplings^ and GO combination pedals aud pistons. The extreme range of compass from the highest to the lowest notes is nine octaves apart. There are four sets of manual keys and one set of pedals. The manual keys extend from C C to C in altissimo, or sixty-one notes j aud the pedal from C C C to G, or thirty-two notes. The pedal organ consists of twenty-Biie stops, tho choir organ of twenty stops, the greut organ of twenty-five stops, the swell or-au of twenty-five stops, the solo organ of twenty stops, and there are fourteen couplors. Eight pnenmatic combination pistons govern the wholo of the stops of each manual range of keys, and those ate so placed below and in frent of the keys as to be at nil times within instant reach of the Lauds of the performer. Six pedals govern the stops of the pedal organ. The "Swell " is, as usual, in tho rear of the organ, and will be in a

separate chamber, 20ft. by 20ft, and 20ft. hrgfa The key notes, or " claviers," as they are technically called, are made of massive ivory, and so exquisitely balanced that the least touch is sufficient to sound them, and, in fact, notwithstanding the size of the organ, any lady could play upon it with the same ease and with the same rapiditv as she could on a cottage piano. If anything, the notes are almost too easily sounded, and scarcely give that rest for the hand to which organists are so much accustomed. This, however, is a fault on the right side, and one which will bear good fruits when rapid and brilliant execution ig needed to develop the infinite variety of tone of this great instrument. All the internal metal pipes are made of an alloy of 5-9ths tin and 4-9ths lead. The front pipes arc almost entirely of tin, there being 90 parts of that metal to only 10 of lead. The outer pipes are burnished and polished in the same manner as those of the great continental organs ; the burnished metal, in fact, is made the chief ornament, and a most effective one it is. The organ will be supplied with wind by -means of steam power, as in the case of the Liverpool organ in St. George's Hall. Mr. 1'euu i.s making two eight-horse power engines for this -work, which will be able to work up to 50-horee power with ease and give the very deoided pressure of air required for playing with full power when all the stops are opened. The maiu reservoirs into which the compressed air is forced are placed in a chamber in a dry position. The feeders supplying the air are of a most ample size, and constructed to receive their wind from the room above, and not from the locality in which they are placed. To carry out this arrangement, which is one of the highest importance, passages are provided for the windshafts to and from the organ to the chamber in which tho main reservoirs are placed. The main reservoirs in turn deliver their wind to numerous subsidiary reservoirs iu immediate connection with the pipes. The mechanical arrangements effected by tho pressure of attenuated and compressed air vary from four to forty inches. The light touch of all the key-notes is alike. The pedal arrangements are divided into ten distinct parts. The external aspect of the . grand organ is very imposing. It is uotdiefi»ured by a case. The pipes, carefully graduated as to height, rise in four great clusters of spires, two at each end and two in the centre. In the three sides which front the audience are three vaulted lofty openings which allow all the works to be seen, and in the background is a perfect forest of pipes. The base, or stand, of the organ is about 21ft. high. This is of curved oak with a recessed Italian doorway in the centre, in which, at the keys, the performer sits. The oak Bereeu which forms the external face is, however, merely a screen, for the organ itaelf is built on massive stone foundations, which the oak work encloses. The instrument will cost, when completed, about £10,000. It has been built under the direct supervision of Sir MichaelJCosta, assisted by Mr. Bowley, of the Crystal Palace, and Sir Michael pronounced it to be perfect in tone aud working.

THE DETERMINATION OF THE FEB-
CENTAGE OF SULPHDK IN IRONS.

rilHE analysis of irons is becoming increasingly
-*- important, and the small qnantities of im-
purities, whioh greatly alter their quality, renders
accuracy indispensable, and adds to tho difficulty
of ensuring it. Although not sulphur, but phos-
phorus, is the greatest hindrance to the produc-
tion of good iron, being generally present in a
larger quantity, the former is nevertheless inju-
rious. It may therefore be acceptable to those
who are interested in the subject if I describe the
method which has to my mind been the most
satisfactory in the estimation of the quantity of
sulphur in irons. I have analysed several speci-
mens of pig iron according to the solution in
nitrochloric acid method, with all due precau-
tious, which, although exceedingly important, are
often omitted in explanations of the process. The
following are results of the analyses :—

Sample 1st anal. 2nd anal. Dif.

No. I. percent, of S. 0 48
No. II. o-62

No. III. „ „o-45

*o. IV. „ „ 0 23

The precipitate with chloride of barium does not make its appearance u'jtil after warming the

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^lotion for some time. After filtering and washing it well with boiling water it is saldom if ««r possible to render it white, which is objectionable to a careful chemist. However, if the sulphate i» precipitated it all, I am convinced that it is entirely preeipttated, and with such results as I hare given above there is scarcely cause to complain much of the process.

As, however, puddle bars contain a very small quantity of sulphur, at least 10 grammes of iron in fine powder must be employed in order to obtain a weighable and reliable quantity of sulphate of b irium. More acid must consequently be used, and it i» impossible to obtain a precipitate in the strongly acid solution, which, for well known reasons, must not be neutralised.

I will, therefore, briefly describe the method which I have employed to estimate sulphur in puddle bars and other irons containing small quantities of that element—a method which has given me highly satisfactory results.

A weighed quantity of iron is thrown into a rapacious flask (about 2 pints capacity) ; about an ounce of water added, and the whole agitated to prevent caking in the after processes. A cork having two perforations is inserted into its mouth. Into one of these perforations passes a tube with bulb and funnel bent and containing a little mercury to allow of pouring into the flask, but to prevent back action. Into the other passes a tube bent at right-angles leading to a JJ tube, containing emstic potash free from sulphate. (Beyond this JJ tube I placed another containing hydrated oxide of lead in solution by caustic potash, which after repeated analyses was not in the slightest degree blackened.)

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ON THE POLARISATION OF HEAT. *
By Professor Tyndall, F.R.S., &c.

IN the Philosophical Magazine for November,
1835, the late Principal Forbes gave an
account of the experiments by which he demon-
strated the polarisation of non-lnminoas heat.
He first operated with tourmalines, and after-
ward*, by a happy inspiration, devised piles of
mica plates, which from their greater power of
transmission enabled him more readily and con-
clusively to establish the fact of polarisation.
The subject was subsequently followed up by
Melloni and other philosophers. With great
sagacity Melloni turned to account his own dis-
covery, that the obscure rays of luminons sources
were in part transmitted by black glass. Inter-
cepting by a plate of this glas-j the light emitted
by his oil lamp, and operating upon the trans-
mitted h?at, he obtained effects exceeding in
magnitude any that could be obtainod by means
6T the radiation from olscnrc sources. The
possession of a more perfect ray-filter and a more
powerful source of heat enables us now to obtain,
on n greatly augmented scale, the effects obtained
by Forbes and Melloni.

Two largo Nicol's prisms, such as those employed in my experiments on tho polarisation of light by nebulous mitter, were placed in front of an clcctrie lamp, and so supported that either of them conld be turned round its horizontal axis. The beam from the lamp, rendered slightly convergent by the camera-tons, Hydrochloric acid is poured in at the funnel, J was sent through both prisms. But between them

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and suction applied to draw it through the mercury into the flask; sometimes water is added, and then acid, until there is a large exoeess of acid. When the action, after due addition of acid, is \erj slow, the contents of the flask are boiled, then the flame taken away, and as soon as ebullition has ceased air is sucked through the apparatus. The boiling can after be advantageously repeated, and the suction again continued. The •till caustic solution in the (J tube is emptied and rinsed out into a beaker. Pure chlorine gas is passed through it j after boiling, sufficient hydrochloric acid it added to drive off the hypochlorous acid, and the boiling is continued until all or nearly all tin smell of this acid is gone. The sulpiiate is then precipitated with chloride of barium.

The contents of the flask are filtered through asbestos. A small funnel with a rather ill-proportioned large neck is chosen. Enough asbestos loosely to fit into the neck is taken and thrown iato the funnel, without any placing or pressing with the fingers. Oa pouring water in to fill the funnel, the pieces of asbe-tos swim about in the liquid, and gradually settle in the neck in Buch a manner that the acid solution can be filtered quickly and perfectly clearly. After it has all gone through, the flask need not be rinsei out, or the residue in funnel washed; but the latter should be transferred with the asbestos to the flask again, and the funnel washed with a very small quantity of nitrochloric acid, which is allowed to trickle into the flask also. The black residue mixed with nitrohydrochloricacid in very email quantity is heated, covering the mouth of the flask with a glass plate. Some water and carbonate of soda is added to take off the excess ef acid, and the liquid, after boiling, is filtered through paper, taking care that it is still slightly acid, and, of course, washed. Chloride of barium ia added to this solution, and if, as is often the case, a precipitate be produced, the whole is poured into the beaker with the former precipitate, and treated in the usual manner. By this method I obtained highly satisfactory results from irons which, according to the other process, would not show the least sign of precipitation when

was placed a coll containing iodine dissolved in bisulphide of carbon in quantity sufficient to quench the strongest solar light. Behind the prisms wasplaced a thermo-electric pile, furnished with two conical reflectors. The hinder face of the pile received heat from a platinum spiral through which passed an electric current regulated by a rheostat.

The apparatus was so arranged that, when the principal sections of the Nicols were crossed the needle of the galvanometer connected with the pile showed a deflection of 90° in favour of the posterior source of heat. One of the prisms was then turned so as to render the principal sections parallel. The needle immediately descended to zero, and passed on to 90° at the other side of it. Reversing, or continuing tho motion, so as to render the principal sections again perpendicular to each other, the calorific sheaf was intercepted, the needle doscended to zero and went up to its first position.

So copious, indeed, is the o\v of polarised heat that a prompt rotation of the Nicol would oanse the needle to spin several times round over itB graduated dial.

These experiments were made with the delieal galvanometer employed in my researches up "j radiant heat. But tho action is so strong as to cause a coarse kcture-ro"ra galvanometer, with needles 6in. long and paper indexes a square inch each in area, to move through an arc of nearly 180°.

Reflection, refraction, dispersion, polarisation (plane and circular), donble refraction, the formation of invisible images both by mirrors and lenses, may all be strikingly illustrated by tho employment of tho iodine filter and the eleotric light.

Take, for example, the following experiments: —The Nicols being crossed, the needlo of the galvanometer pointed to 78* in favour of the heated platinum spiral behind the pile. A plato of mica was then placed across the dark beam with its principal section inclined at an angle of 45" to those of the Nicols. The needle instantly fell to zero, and went up to 90" on the other side.

* From tho Philosophical Magazine.

And, for circular polarisation :—The Nicols being crossed and the needle pointing to 80g in favour of the platinum spiral, a plate of rock crystal cut perpendicular to the axis was placed across the dark beam. The needle fell to aero, and went to 90a on the other side.

The penetrative power of the heat hore employed may be inferred from the fact that it traversed about 12in. o£ Iceland spar, and about llin. of the cell containing the solution of iodine.

ON THE PHENOMENA OF COM-
BUSTION.

SPECIAL REPORT.

THE last of the present series of Cantor Lectures on this subject was delivered by Dr. Benjamin Paul, F.C.S., on Monday, 28th ult., in the presence of a large audience. The lecture had specially to do with tho use of combustible materials for producing li^ht, with the varieties of illuminating materials—coal gas, potrolcum, and paraffin oil, and also with the measurement of tight. At the outset, the lecturer observed that the evolution of light was another of the effects of combustion which was of practical utility. It was chiefly by means of combustion that artificial light was produced. One important fact we hail to consider in regard to combustion as a source of light was that all moterial substances became luminous when tbey were sufficiently heated, and this was a special characteristic of solid substances, which, howover, were not changed in their condition or nature by such heating. Having shown the luminosity of solid substances by experiment, Dr. Paul adverted to the fact that liquids also became luminous when heated, under conditions, however, when they were not converted into vapour. Melted metals and glass, for instance, emitted light at high temperatures ; gases a«w vapours were least of all capable of luminosity when heated. At a temperature of 1000 degrees, liquid substances emitted a reddish light, and this degree of heat was termed "red heat," which again, in proportion to the temperature, was distinguished by the names " red," or " doll" heat; oragain bythose of "cherryred " or "brick red." At very high temperatures, solid and liquid substances gave a colourless light, termed " white heat." To produce artificial light, we must first obtain a very high temperature in some substance capable of becoming luminous in that condition. If hydrogen gas were burned with oxygen, a very intense degree of heat would be attained, but the water vapour which was the prodnct in this gas had such a degree of continuity that it gave a gas affording barely sufficient light to be visible. After explaining the production of lime-light, and showing some experiments with niagnesin, the lecturer adverted to carbon. Carbonaceous substances were easy to illuminate. Tho chief characteristic of very inflammable substances was the presence of carbon, which in some cases was as much as 80 per cent. Oil, tallow, and the various materials used in lamps were susceptible of vaporisation, and that, too, without giving any fixed carbonaceous residue, which was not the case with ooal, wood, resin, or such materials. Dr. Paul next asked attention to the form of flame, which, he said, was partly determined by tho way in which the corobnstible gas was supplied, and partly by tho reaction of the heated product of combustion and the atmosphere upon each other. The shape of tho luminous flame might be different from that of a candle, but in every case there was tho same relative disposition of the zones in which the progressive changes took place. The production of flame from any substance corresponded to the amount of carbon it contained, and to this was owing the difference between the flame from a candle and that from coal gas. After some remarks on tho comparative merits of defiant, marsh, and benzole gases, tho lecturer alluded to paraffin oil, and said that, whereas marsh gas contained 73 per cent of carbon. paraffin oil contained 85, and the former contained half aB much carbon as olofiant gas. The vapour of marsh gas contained one-seventeenth as mnch carbon in a given volume as tho vapour of paraffin, which was very much more dense. The same was the case with bansole gas, which contained four times as much carbon as an equal volume of marsh gas. The latter gas burnt with a pale flame, leaving no sooty depnsit or luminous effect, and the former burnt with an intensely- luminous flame, and over and above that left a large doposit of carbon, which, unless regulated, rendered the flume sooty and smoky. In all illuminating material! it was necessary to regulate the conditions in such a way that we might get a deposit of carbon to such an extent as would make a flame in the highest degree luminous;, without overstepping the line at which it became smoky. The lecturer next referred to the heat of rooms, and observed that most people seemed to forget that in proportion to the quantity of artificial heat introduced into a room in that proportion was the air deteriorated, defiant gas produced the greatest effect upon the atmosphere, by destroying the largest amount of air; marsh gas next; carbonic acid gas next, and hydrogen gas least of all, because it was the most volatile. Dr. Paul then referred to the complaints so rife relative to the bad quality of the gas now supplied, and said that although these complaints might to some extent be based on just grounds, yet he thought much of the fault lay with the burners in use. He here exhibited some of Mr. Sugg's improved burners, and concluded by regretting that the time at his disposal had prevented him from entering into the interesting subject of paraffin oil.

We understand that the next series of Cantor Lectures will be given by Dr. Williams, on "Fermentation," and that they will take place on the last two Mondays in April, and the first two Mondays in May.

8TRUCTTJRE OF THE LIVER.

AN important paper on this subject by Professor Hering, of Vienna, appears in the just published third part of Strieker's Handbuch •*>« den Oeneben. This gland is the most intricate in the body of the higher animals, and its functions present a corresponding complexity j on these grounds it has been subjected to very careful microscopical examination, as well as experimental investigation, by many of the best observers, both here and abroad, amongst whom Professor Hering holds B distinguished place. Speaking broadly, the liver consists of an immense number of pear-shaped bodies or lobuli, separated from one another by a delicate investment of connective tissue. Between these spread branches of the portal vein, conveying blood to the liver from the intestines, and of the hepatic artery, the ultimate branches of the latter discharging themselves into those of the former. The capillary vessels thus formed penetrate the substance of each lobule and reunite in a central vessel, which, issuing from the extremity of the lobule like the stalk of a pear, coalesces with others to form the hepatic veins which convey the blood that has circulated through the organ to the heart. The substance of the lobnli themselves is composed of cells, the office of which is in part to secrete bile, and in part to produce the substance termed glycogen. The writer cbt-erves that the capillary system of the portal vein, as a general rule, exhibits large capillaries and a narrow-meshed plexus, whilst that of the hepatio vein exhibits small capillaries and a plexus with wide meshes. The foregoing facts are now fairly established, but the poiuts to which Professor Hering's attention has been particularly directed are connected with the distribution of the biliary ducts. These, he states, consist of a close net work of delicate canals running between the hepatio cells, with meshes equalling the cells in diameter, or, in other words, the canals run between the flat surfaces of two adjoining cells. The capillaries, on the other hand, occupy the angles formed by the junction of three or more cells. This description particularly applies to the rabbit. In man and the dog, biliary canals are also found at the angles of the cells. For the sake of clearness, we have made use of the term biliary canals, but Professor Hering observes that they have no proper wall so long as they are contained within the lobuli. These walls are, in fact, the cells themselves, and they may fairly be represented by the tubes that would be produced by grooving two solid bodies, and applying the corresponding channels to one another. He has not been able, in any instance, in the rabbit at least, to discover a blind extremity of a biliary tube. He describes the hepatic cells as presenting various forms, according to the direction in which they happen to be divided in the section, being sometimes quadrangular, sometimes polygonal, and presenting the grooves above mentioned for the passage of the capillaries, and for the formation of the ducts. They contain one,

or occasionally two, nuclei of spherical or elliptic shape, together with some granules of biliary pigment and fat molecules. He finds the liver to be richly supplied with lymphatics, which, as in other organs, chiefly accompany the connective tissue. The system presents this peculiarity, however, that both the capillaries and the larger vessels freely anastomose with each other. Though he has carefully examined! he point, he has been unable to follow the nerves of the liver into the cells, a relation which has been maintained to exist by Pfluger. (Academy, No. II., p. 47.) Professor Hering states distinctly that all demonstrable nerve trunks lie outside the lobuli.

PLATINISED LOOKING-GLASSES.* By C. Widemahn.

(Continued from page 27.)

IT is now unnecessary to use glass free from colour or to require parallelisms of the two surfaces. Bubbles of air, stripes, foreign bodies, pieces of the pots, &c, &c, do not interfere with the process. There is then an economy of 50 per cent, in the glass.

In order to manufacture a looking-glass of 5 millimetres thickness, they use at the St. Gobaiu works a plate measuring 10 millimetres thickness.

At the Wailly-sur- Aisue works, plates are used having but 75 millimetres thickness, as it is only necessary to polish the glass on one side. From this a saving is made* of 25 per cent on the thickness of the glass.

Very correct calculations show that Mr. Dode secures an economy of SO per cent, on platinised glasses, as he uses for that purpose only inferior glass commonly used for flagons; even common brittle glass can be used without the least difficulty. To this saying there is another to be added, which will astonish the reader. A square metre of glass absorbs about 183 grammes of mercury and 550 grammes of tin, representing about a cost of 4 francs, 40 centimes. A square yard of platinised glass costs 1 franc and 20 centimes for platina. It results from this, that at the Wailly-sur-Aisne works, the superficial square yard of platinised glass is sold at an average of 25 francs. This price is doubled in the mercury manufacture.

There is another circumstance for which this new process is recommended to the public. It is with great difficulty that mirrors are obtained with a curved surface. By the plating process this difficulty disappears, and it is as easy to manufacture curved, round, etc., as horizontal mirrors. There is also no inconvenience arising from upsetting the glasses in transportation or in placing them in the frame.

Already in this country a company has been organised to manufacture reflectors by the means of silver mica leaves on the posterior face, and fastened together so as to obtain a large reflective surface possessing the desired curves. They are cheap, and easily repaired; but they meet with two great difficulties: the quick alteration of the silvery surface caused by the hydrosulphurous gases of coal with which locomotive reflectors are always in contact, and the want of transparency of the mica and its yellow colour. I have no doubt that by the adoption of the platina these evils would have found their remedy, for, as it has been seen before, the reflecting surface is on the anterior part of the glass.

A quite peculiar property of the platinised mirrors will no doubt be applied by architects. The platinised glasses forming mirrors are transparent when the light passes through them. A person placed in the rear of an office can see everything going on in the front office without himself being seen. I insist particularly on this property; it appears to me to give to the platinised glass quite a new application, which will increase its sale. This transparency is easily explained considering the small quantity of platina deposited on the glass, which quantity is not large enough to give opacity to the glass and prevent the luminous rays from passing through it. This transparency has received a very amusing application quite lately in Paris. Mirrors called mirrors a surprise, are sold, which, when a black paper at the back of the glass is removed, allows a photograph or any other image to be seen through the metallised surface appearing as

a spectre; this photograph is simply applied at. the posterior side of the reflecting part, and oiled in order to add to its transparency. This toy is varied in very different ways, and has just been applied in the new play of "The White Cat," at Paris, and has caused an immense sensation. So I have no doubt that the inventive mind of the Americans will find thousands of applications for this property, either in applying it to the decoration of stores, or to external ornamentstion. In theatres or concert halls among flowers it produces the most fairy-like effect. The window glasses of a parlour made thus would transparent in daytime, and at night when the shutters are closed the whole window woud appear as a large looking-glass, and reflect all lights and objects in the apartment.

The manufacture of glasses with amalgam necessitates great labour. In order to obtain 50 metres of looking-glass a large number of hands and a large plot of ground are required. These glasses must remain loaded with weights from 15 to 20 days; then 20 days more are required to eliminate the superabundance of mercury, and three months more are required before they are saleable; not to mention all the precautions that have to be taken at every moment in the shipping and setting in frame. MM. Dode and Faure are able to platinise a surface of 800 metres a day, with only the aid of a few hands, as one workman is able to platinise 50 metres of glass in 12 hours' work.

• From the Scientific American.

EXHAUST STEAM FOR HEATING PURPOSES.

By Charles E. Emery.

QUESTIONS are frequently asked regarding the relative economy of heating buildings with live steam taken direct from the boiler, or with the exhaust steam from a non-condensing engine.

Though the steam engine is a heat engine, the best examples utilise only ten per cent, of the heat in the steam used, consequently at least 90 per cent of the heat which enters the cylinder escapes with the exhaustiog steam, and can be made available in no way except for heating purposes.

The temperature of the exhaust steam from a condensing engine is from 130* to 140s Fahr., and that from a non-condensing engine is from 2129 to 220" and upward, varying according to the amount of back pressure in either case. A portion of the escaping heat is generally utilised in heating the feed-water for the boiler. Ia the condensing engine the low temperature of the exhaust steam, and the liability to'air leakages and loss of vacuum in long pipes, makes it impracticable to save any more of the heat than that mentioned, and the remainder is necessarily wasted in heating the condensing water. In the non-condensing engine there is on the average ten per cent, of the best utilised by the use of a feed-water heater, in addition to the ten per cent, transmuted into work, consequently eighty per cent, of the original amount of heat remains in the exhaust steam, and is usually wasted in the atmosphere. If this large quantity could be used for heating buildings without interfering with the performance of the engine, there would be no doubt of the value of the system—the heat in fact would cost nothing; but it is evident that in order to cause this steam to traverse throngh heating-pipes and coils it must have sufficient pressure in excess of that of the atmosphere to enable it to overcome the increased resistance. The additional pressure varies from two to five pounds and upwards per square inch, and acts as so much back pressure upon the piston, thereby reducing the power of the engine. The power lost must be supplied by increasing the mean pressure upon the driving side of the piston, and the question becomes :—What is the relative cost in fuel of supplying the heatingpipes with steam direct from the boiler, as couipareJ with that required for the extra power necessary to circulate the exhaust steam through the building?

The answer to this problem depends upon the particular circumstances of each case, and to make the subject generally understood, it is first necessary to investigate some of the known facts in regard to low-pressure steam-heating apparatus.

Manufactories where steam-power is employed generally hare a large number of windows for the convenience of the workmen, and are often more or leas exposed to cold draughts from hoistways, staircases, and outer doors, and though the temperature need not be so high as in dwellinghouses, it would be unsafe to allow less than one square foot of heatirig surface in the heating pipes and coils to every 100 cubic feet of space to oe heated. In order to form a safe estimate of the amount of fuel required when the steam is taken direct from the boiler, we may assume as an extreme case that the difference between the external air and that of the room is to be eo^; then, according to the experiments and formula of Tredgold, we find that it will require three .and one-eighth square feet of surface to condense a pound of steam per hour, and if one ponnd of coal evaporate eight pounds of water, it will supply steam to (8 X 3125 =1) 25 square feet of heating surface and will beat (25 x 100]=) ■2600 cubic feet of space for one hour. This estimate will be correct for average circumstances, out will not apply to all cases of low-pressure steam-heating, especially where the rooms are unusually exposed either to draughts of air, or .great extremes of temperature.

In estimating the greatest amount of space that can be heated by the exhaust steam of an engine, it should be borne in mind that the quantity of steam discharged necessarily varies with the work being done, and as the temperature of the building requires to be constant, we can only utilise the quantity of heat escaping when the [engine is lightly leaded. For instance, an engine of 80-horse power may be loaded occasionally to only 40-horse power for half an hour or more at a time. If each horse power require o n the average 31b. of coal per hour, 40-horso power will require 1201b. As has been before mentioned, the exhaust steam from an engine contains 8-10ths of the heat received from the fuel, so in the present case the maximum heating effect is equal to 8 -10th of 1201b., or 961b. of coal per hour; and as each pound of coal will beat 2500 cubic feet of space, 951b. will heat 240,000 cubic feet, equal to 'the capacity of a building 100ft. long, 60ft. wide, and 40ft. high. The extra power required to overcome the back pressure in that sized engine could not well exceed 10-horse power, which would cost 301b. of coal per hour j And as 961b. would be required were steam taken direct from the boiler, the saving is (96 — 30=) 66/b. per hour, or 68 per cent. If the quantity of .space heated be less than that mentioned, the percentage of saving will be less; for instance, to heat 150,000ft. of space in the ordinary way would require 601b. of coal per hour; but with the exhaust steam in the above instance the cost will still be 301b., so the saving will be 60 per eeat. In warm days in winter, when less heat is required in the buildings, the same power will be taken from the engine to supply the less quantity of heat, so that the percentage of saving will be less. There would be some saving, however, whenever it required more than 301b. of coal to heat the rooms. In case each horse power required more coal per hour than that stated, the advantages of exhaust heating wonld be correspondingly diminished, unless the size of the engine and amount of power necessary to distribute the steam were also less. Iu some instances, probably, the system is productive of loss as compared with the nse of live steam, so the true plan is to make accurate calculations in each case. The following directions may therefore assist many readers—

To ascertain whether heating by exhaust steam is economical where it has already been applied, the first step is to measure the extra back pressure on the piston, which can be done by indicating the engine when the steam is escaping freely into the atmosphere, and when the exhaust is throttled for heating purposes, sand comparing the back pressures shown by the diagrams. If this be not convenient, one leg of an inverted glass siphon containing mercury may be connected to some enlargement of the exhaust-pipe, and the mean difference in level noted in the two cases the same as before. One pressure corresponds to about 2 (2037) inches of mercury. A longer syphon filled with water may be used with some inconveniences. In snch case, one pound pressure corresponds to a column of water 2-3 feet high and CO8 temperature, or 2-4 feet high at temperature of 206°.

Having ascertained the extra back pressure, the horse-power required to overcome it may be ascertained by the following rule, \iz.: Multiply t cgeiher the back pressure, the area of the piston

in sqnare inches, and the speed of piston in feet per minute, and divide the product by .33,000.*

The next step is to ascertain the coal required per horse-power per hour. This should be done, when practicable, by regular experiment. In other cases, it may be assumed that engines working with a steam pressure of 501b. and nnder, with little expansion, will require 5 to 61b. of coal per noree-power per hour. With more expansion, 4 to olb. will be required ; and the most improved form of expansive engines, working with steam at 801b. pressure, will furnish a horse-power for 31b. of coal per hour. By multiplying the horse-power due to the increased back pressure by the coal required per horse-power per hour, and the product by 2500, the result will be the least number of cubic feet of space wbicb can be heated economically by the exhaust steam from that engine. The advantages nnder different circumstances may be ascertained in the manner previously stated.

In heating a building by exhaust steam, particular attention should be given to the size and arrangement of the pipes. A main exhaust pipe should be run up through the building and out of the roof in the usual manner. This pipe should

REVIEWS.

Continental Farming and Peasantry. By Jf-AB. Howard, M.P. London: W. Bidgway, 169 , Piccadilly.

THE comparison of results obtained from two opposite systems must always decide the question. Mr. Howard's book in this manner contributes to settle the question of large or small farming. Travelling himself through the farming districts of France and Belgium, where small holdings prevail, he shows not only that the produce does not equal that of English farming, but that the holders are worse off ; do more work for less money with less results than English farm labourers, although possessed of the advantages of a more favourable climate. Mr. Howard would permit small holdings on large estates as rewards held out by the owner (as iu the case of Lord Lichfield) to deserving and thrifty workmen in later life. He would not, however, encourage tho snb-division of holdings into smaller lots. One fact which he calls attention to is worth notice,

namely, that in Belgium, where the small farm . system is Baid to obtain such favoar, the Trades' be larger than is ordinarily employed, so as to TJnion Confess, which met some time back at form a kind of expansion chamber to equalise Brussels, condemned the system of "petite culture,'' and resolved that when communism in land

the exhaust pressure From the vertical exhaust pipe the heating pipes may be led out for each floor of the building. A common plan is to put a good-Bized cast-iron pipe under the workbenches along the sides of the rooms. Such pipes should be connected by bolted flanges, and ample provision made for expansion and contraction. Heating coils of the ordinary construction may also be used, care being taken to make the leading pipes with as few bends as possible and of sufficient aize. To obtain the proper size of pipe for a given cose, tho following formula may be used, which is founded on some experiments made by the writer for tho United States Government, viz. : a - W -~ 46 (p + 3) in which a = area of steam-pipo in square inches, W the weight of steam iu pounds delivered per hour, and p tho difference in pressure. Assuming as an extreme that 2-4 square feet of surface (a) will condense one pound of exhaust steam per hour, then, when the difference in pressure equals one pound, a - s -7- 440. The following is then a safe rule :— Divide the heating surface in square feet by 400, the result is the proper area of the pipe in square inches. The following table gives the amount of surface which will be supplied with steam throngh pipes of the sizes mentioned:—

Amount of Surface.

Diameter of Pipe, rinch

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The pipes should be slightly inclined, so that the condensed water will move in the same direction as the steam. The ends of the various heating pipes and coils should be connected with a water-pipe terminating near the boiler in an inverted siphon, the shorter leg of which should be about seven feet long. The bend may extend under ground if necessary. This siphon should deliver the condensed water into a tank where it can be returned to the boiler. An air-cock should be placed in the water-pipe to allow the air to escape in starting.

Arrangements should be made so that the exhaust steam can be shnt off from each room separately by a valve, and in some instances it may be desirable to admit live steam into portions of the pipes when the engine is net in motion.—American Artisan.

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THE LUMINOSITY OF PHOSPIIORTJS.-Herr W. Muller, of Perleberg, gives an explanation of the well-known luminosity exhibited by phosphorus iu the dark. It depends on slow combustion or combination with oxygen, but does not taku place in pure oxygen, except when it is diluted by other ga60s, as is the case in the atmosphere. In other atmospheres, as hydrogen or nitrogen, tho phenomenon does not occur.

• Many engineers will find the following formula moro convenient:—

<Ptrp
H.P. =

2*2,000 which, put in the form of a rule, is: Horse-power equals the square of the diameter (di in Inches, multiplied by the length of a single stroke (s) in inches, multiplied by the number of revolutions per minute (r), multiplied by the extra back pressure lp), and divided by 252,000.

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