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tion thns obtained available, and sufficiently identities the specimen. As tho collector pursnes his investigations month after month, he will find his senses becoming educated to a delicacy of tmich and fineness of perception that cannot fail tobe a source of pride and gratification to him. He whose attention would not fit first be diverted to the ragged leaves of a caterpillar-ridden tree will in a few months notice instantly the slight convexity of ontlinc on twig or leaf caused by the presence of a small insect, or the extremity of a branch cleanly cnt by a pinner-beetle.

Iu the conreo of his observations he will be amused by tbe imitative shapes and colours of many forms of insect life, and will frequently be deceive'! by the Ourculios, who successfully simulate buds and bits of bark. The caterpillars of some of the moths resemblo so closely cylindrical twigs, as many of the Loopers {Gi'onurtridai): scales of roui;h or smooth bark, as the Hug-moth (Limacodes pitheeinm) and tbe Lappet-moths (Gastropatka veieda and Americana'). Soino of the beetles, as the Vrytocepliali and ITM*i-is, closely resemble seeds, as do certain lings, among them Corhn't'li'i'na, and the two latte- snggest such kinship as to cause them almost invariably to fraternise i'l the cabinet of the amateur. These singular resemblances are called mimct с forms; and, existing everywhere in nature, even if they have no higher signifiennce and serve no better purpose, educate our perceptive powers to a degree undreamed of by tbo careless lvmle of money worshippers, Luring the active season of the insect year the collector should make it a rule never to stir abroad without a cork-stopped vial halt tilled with alcohol, for tbe temporary depo sit of beetles, ants, or the larva: or pupa: of any insects that it may be desirable to preserve in this way. The only insects that are irrecoverably injured by a few days' immersion in puro alcohol are the butterflies and moths. For these a small cork or pith-lined pocket-box, of convenient form, and fall i J in. in depth, containing a few insect pins of vari'-us sizes, is indispensable, and should be a constant companion. Upon a premeditated excursion of a day or more in duration, the collector will naturally provide more extensive means of transportation, such as jars of alcohol, a vial of chloroform, a number of old envelopes a large box slung on side with straps, and a proportionate stock of pins. JSome collectors continually carry, in a pocket made for the purpose,ja wide-mouthed vial, liko a chemist's test-tube, " of the same size all the way up," containing at the bottom a few <;raios of cyanide of potassium, which is kept in place by a wad of cotton, felt, or thick cloth, neatly pressed down upon it. This prevents the Cyanid», which is n deadly poison, from touching or soiling any delicate insect, and allows the powerful vapour to destroy, as it does almost instantly, the life of any insect that may be inclosed in tbe prepared vial. The permanence of this poison (its virtuo enduring for я twelvemonth or more), its cleanliness, and cheapness, render it perhaps the most convenient and desirable "life annihilator." It is, perhaps, unnecessary to mention that the vial should be kept tightly corked, and that the insect should remaiu therein not much more or less than ten minutes. Л vial, lin. in diameter and 4in. in length, made of strong glass, is the most desirable size. Some collectors carry a small vial of chlorofrrm, through the cork of which passes a very small tube of metal; what is called by jewellers "hollow wire,'' of minute aperture, is u'cd for this purpose. This instrument is nscd for conveying a limited identity of chloroform to the spiracles of the insect, without deluging and damaging much of its plumage, if furnished therewith. Ether, ¡is well as chloroform, is sometimos used in 1 eu of the cyanide, but it haï to be continually supplied from another reservoir. In some countries bruised lauiel leaves arc placed in the bottom of the vial, or a small packet of them pinn?d in a corner of the collecting-box, inclosed iu a little bug or wisp of loosely-woveu cloth, such lace, hook-musliu, &c. All of these poisons act at first only as anesthetics, or stupifiere, and should be continued in use sufficiently long to destroy vitality, or to prevent tb estrugglos oí tbe insect; for by these struggles it injures itself, as well as its companions, alter being piuned in tbe collectinf; box.—The American- Entomologist mid Jtotanist.

SCIENCE FOB THE YOUNG.

Sttheeev. E. Kern An, Clongowes College.

(Continued from page 269.)

CHAPTER III.

§ I.—Forces Applied To л Point.

To have equilibrium there must be at least two forces. From their conditions of equilibrium, that of many forces is easily drawn. Forces (two) may act on a body, opposite, or at an angle.

No. 1. Laws. These include any number of force* in either of the possible positions. 8ome laws may appear too self-evident tо be mentioned, still they are not the less true laws.

Law I. Туго opposite forces are in equilibrium when thoy arc equal оно to tbe other. Equilibrium is otherwise impossible.

Law II. Many opposite forces are in equilibrium when their algeb-aical enm iseqnul to zero. Suppose three forces P Q K. they aro in equilibrium when P -f- Q — R = O. Any number connected by the signs -f- and — (as they aro at one or other side of the body) Bin! reducible to zero, are in equilibrium.

Law III. Two forces at an angle cannot be in equilibrium without at least a third. It is not possible that two forces acting at an angle on a body be in equilibrium ; the \vnly mnst move, until they come into a straight line.

Law IV. Two forces at an angle may be replaced by a single force, represented by the diagonal of a parallelogram constructed on t/te two forces. The liues which represent tbe two forces acting here on a body, arc supposed to have each a length proportionate to the intensity of the force which each represents. When the parallelogram which those lines admit is completed, the diagonal from the point of application represents in intensity and direction the resultant of the two forree.

Law V. Two forces at an angle will be kept in equilibrium by a third force, equal and opposite to their re-nltant.

Law VI. Many forces in tbe same plane may be reduced by " composition " to two, which can be eqnilibiiated by Law V. Several forces applied to a point can be combined two by two, so as to leave one pair, the resultant of which can be stopped by an eqnal and opposite force. The whole system is then in eqnilibrium.

Law VII.—Many forces indifferent planes can be reduced to a résultait, which is cquilibriated by Law I. Several forces in different planes and directions can be so combined by one or other of the preceding laws that that there be left but one force.

No. П.—Proofs.

Law I. The body is equally acted upon atbo'h sides; there is no cause to determine motion in one or other direction. As nothing tends to overcome the inertia of the body, it is at r-:st. Experi

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Тпкпе is, near Grenoble, what gui'le-books call a burning fountain. J'rof. Kwoult, who has Lately visited Ibis phenomenon, has published a short account of it. It is an emanation of mixed (rases. The chief constituent Is marsh (ras, and there- arc small <]uautities ol carbonic »cid aud oí oleflaut gas.

a A

mentally, Fig. 05. The two forces P and Q acts upon the body A. Their action is effected by the weights p //. No matter what these weights, as long as they arc equal no effect of motion is seen in A. Raise geutly one of the weights at one side: A moves towards the other side. Allow that weight to act again; A remains at rest in the new position. Iu the Fig. 55, n raised, A moved, rests at 0.

Law II. As the snm = 0, algebra teaches that, the -f- = — side o£ the equation. Therefore the forces are in the condition of Law I, for a number of forces, in the same direction, act as one equal to their snm. Experimentally, a number ot weights taken lit random are divided into two parts, M and N, calculate the sum of each part. If M — N — 0, the two parts may be hung to the weights p q, Fiir. 55, without disturbing equilibrium. If M — N = » (some indefinite quantity) there will be an effect produced on A, it will movo at least, if the differences (11) be considerable.

Law III. Both forces acting more or less in the same direction, there is nothing to prevent the body from yielding to their joint action. Experimentally, draw down the body A, Fig. 55, let go gently—it is drawn up to the horizontal

position; it is not possible, without puttiro weight nt (a), to have equilibrium at any angle. Law IV. This law contains the famous proposition known by the title of " The Parallelogram of Forces." Its importance is best evinced by the fact that it may be called tbe foundation of all mechanical science. Of the parallelogram of forces there are many mathematical proofs, and some experimental. The latter in general refer too much to the dynamical view of the question to be spoken of in statics. The elementary mathematical proofs are long, tedious, and not perhaps very satisfactory. But thero is a simple yet solid proof based upon a necessary consequence of inertia, which proof will not tax too much the mind or patience of the student. The consequence or principle to be admitted is as follows :—" A force, if allowed to act, must satisfy all its requirements." In plain terms, as before, whatever the force wants to effect with regard to any position in space that it 'must have effected before, it will cease to act. "When such has been accomplished, tho force is exhausted—bas done its work fully. Inertia being a perfect indifference to change of state when the body has acquired motion from a force, it will allow that forco to realise all its requirement« if no external force can interfere. Therefore the body shall move to such a point in space Ps will completely exhaust the requirements of the force. With this principle the proof of the parallelogram efforces is easy anil satisfactory. There are two main points to be proved. First, that the diagonal represents the "direction" which the body would follow if the forces were allowed to act; secondly, that it represents the joint-action or "intensity" of the two forces. Tho whole argument may be got into three short points.

1. The forces P and Q (Fig. 56) applied to the body A, if allowed to act, must satisfy all their requirements.

The point S of the parallelogram is tbe onlv point in spnee at which the requirements will he satisfied. Therefore the body must be found at S, when the forces have satisfied their requirements.

2. The body must have followed the straight line A S (the diagonal) in its passage to the point S, for two points in space are sofficient to determine the direction of a straight line. The starting point A and arrival point В are determined. That the body mnst take a straight line is evident j first, because the forces are supposed to act but for an instant ; secondly, even supposing tho action of the forces continuous, their relative proportion must be maintained. Now, instantaneous force is admitted to produce a straight line, and tho slightest deviation from the diagonal must destroy the relative proportion of tbe forces, for nothing exists to make them act otherwise than parallel to their original direction.

3. The line A S must, compared with Pand Q. indicate by its length the intensity of their joint action ; for, in representing forces by lines, their intensities arc shown by length—that is, the distance from the beginning to the end of a line pictures relatively tho full strength and the complete exhaustion of the forces. Now this is exactly what the diagonal A S exhibits.

To complete this argument, there now remains to be proved ore proposition contained in point 1, which, as it is the chief, so it is tbe longest, in demonstration. Still it is not difficult if taken quietly aud by parts. The proposition is: "The point S of the parallelogram is the only point in space at which the requirements cam be satisfied." It will be readily admitted that if the point S satisfies the requirements for one position, all the requirements for other positions must be satisfied. For greater simplicity, the lines representing the forces will be taken as the positions to be examined; and the three possible sorte of angles which these lines can make (right angle, acute, and obtuse) will make three cases, to be treated separately.

Cuse I. Right-angle (Fig. 57). The requirement of the force P as regards the position M Q, is to place the body M

at a distance from M _ '• s/ R

Q equal to tbe line M P; for M ?being perpendicular on M Q, the length of the foroe P itself shows tbe re-M<> quirement. Now at the point R the body M is at a distance from M Q equal to M P, because (perpondioular between parallels being equal) Q К = M P; therefore R satisfies the requirement of V. On the other side the require

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mente of Q as to the position MP ¡» to place the boiv M at a distance from M P equal to M Q for M Q shows the requirement ot Q, as M Pthat of P. Now at 11 the body is at the dieta nee equal to M Q, as P R = M Q The_ point В the efore satisfies the requirements of both F and С But there is no other point alón* tue diagonal, along the sides, or in space in general ■which will satisfy one or the other; any point ■will satiny these requirements. Various points Tor instance, alone P R will do for P, any point on Q R will do for Q ; none will do for both, as along the diagonal none would do for either. Therefore R is the only point which will satisfy the requirements of the two forces.

Ctaell. Acute angle (Fig. 58). The require

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ment of «he force P as regards the position M Q, is to place the body M at a distance from M Q, equal to P p, which shows the requirement being the perpendicular on M Q from the exhaustion point of P. Now at R the body is at the required distance, as R A, the perpendicular from R on the prolongation of M Q being equal to P p; therefore Pis satisfied. _

The requirement of the force Q m regard ot the position M P, is to place the body M at a distance from M Y equal to Q a, the requirement perpendicular of Q. Now at R the body is at the reqnired distance; R r, the perpendicular on the prolongation of M P, being equal to Q ?. Again, therefore, R satisfies the requirements of P and <& and no other point will do so, &c, same reasoning as in Case I.

Сазе 1H. Obtuse angle (Fig. 59). The re

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the whole fi<nire into rtho acute angle, (this is the chief position shown; the right angle is in light lines; the obtneo angle in dotted lines), the small black xoatfall into position as P j> and its parallel R A., the long black rods may be raised up to the perpendicular as Q q and R r, and pinned there. Draw pine and shift to the obtuse angle. The small black rods, fall again into position, as in the dotted figure, and the long ones can be pinned below, as Q q and R r. The model may be made to range from the most acute to the most obtuse angle.

(To Je continued.)

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quirement of the force P as to the posti is to place the body M at a distanee from M Q equal to P p, the perpendicular from the exhaustion of P on to the prolongation of M Q. Now at R the body is at the reqnired distances, R A being equal to P p. The requirement of Q as regards M P is to place the body M at a distance from M P equal to Q q, the perpendicular from the exhaustion of Q on to M P. Now at R the body is at the required distance,R r being equal to Qq, therefore R satisfies both Pand Q, &c. Finish as in Case I.

Following the same train of reasoning, it could be shown that for any position at R the requirements will be fnlly satisfied. But there is no need of seeking the requirements for other positions, for the points which is necessary for one pair must satisfiy all.

This proof will be firmly imprinted in the miud by drawing lines (forcee) at various angles, and looking for the perpendiculars of requirements; let fall, remember, from the end of the lines representing the forces, on to tho position chosen. This finding of the perpendiculars is the chief difficulty in the II. and III. Cases; once the general run of the reasoning has been understood. The student may be further helped by a model with rods (Fig. 60), which can be shifted to any of the three positions. The unshaded (white) rods nre the forces P and Q, made long to have the prolongations. A pin, a, with chain to keep them at the right angle for Case I. ; two short black rods b Ъ hang from the гор of the parallelogram. They coincide with P and its parallel in the first case. Two long black rods С С, extend from tho end of the parallelogram and coincide wftn Q and its pnrallel in the first case. They can be pinned as the forces. Draw pins and shift

THE SOCIETY OF ARTS ART-WORKMANSIIIP COMPETITION FOR 1870-71.

THE Council of the Society of Arts intend in their Art Workmanship competition of next year to suspend for a time the form hitherto adopted in oflering prizes for art workmanship, believing the change is likely to bo beneficial to the object the Council have at heart, viz.. to see the art workmen of the Unit od Kingdom occupying a good position in the coming International Exhibition in comparison with those of other countries.

With this view the Council have decided upon offering a series of rewards for special excellence on the part of all concurring in tho satisfactory production of works of industry of the highest character. They consider that they can most effectually ensure their object by offerin» to manufacturers the highest distinctions they have it in their power to confer, and to workmen liberal money premiums. They desire to obtain, from those who may be willing to compete for the prizes they offer, specimens of art manufacture, which will have to be sent to the society's rooms by the 14th of January, 1871. These will be immediately judged upon their merits, and the premiums enumerated below will bo awarded. An endeavour will ho made to effect arrangements by means of which every objeot receiving a premium, or selected for the distinction of being exhibited, will be placed in the coming International Exhibition as a contribution on the part of the Society of Arts, showing the result of recentefforts which have been made to improve art workmanship in this oountry. The specimens of manufacture sent in in competition for the above rewards and premiums will have affixed to them the name of the designer and of tho workmen in each special branch of industry involved in the execution of the work. Every workman will bo eligiblü to receive money premiums proportionate to his merits, and to the degree in which he may have contributed to the successful reeultsof the whole, whilst tbe manufacturers may receive the gold or silver medals of the society.

The society hope that they may receive objects enabling tho judges to award the society's gold medal to manufacturers, and the society's silver medal to manufacturers or desiguers—accompanied, in tbe latter case, if the circumstances appear to call for it, with money premiums; and to the art workmen money premiums varying from &'i to £\'0, and to the extent, in the whole, of £500.

These works may obviously include specimens not only of the tasto of the desiguer, but of tho skill of the carver, iulayer, metal worker, chaser, bronzist, engraver, china painter, die sinker, cameo cutter, glass worker, enameller, mosaicist, and other art workmen, either separately or in any combination arranged.

No object involving combined labour for its production will bo eligible for reward uuless accompanied with the names of all those eng»ged in its production, to the most meritorious of whom—whether their works may be exhibited in the rooms of the society or in the International Exhibition—every effort will be made by the Council to give publicity and attract attention.

TESTING! THE DUTY OF STEAM
ENGINES.

AT a recent meeting of the Polytechnic Association of the American Institute, Dr. Vau der Weydc gave an explanation of some of the most approved means of testing the duty of steam engines. As the engine may be considered simply as a system of mechanism for changing heat into motion, economy of fuel is the poin most to be considered in any estimate of the utility or working value of ft given engine; the questions of first cost and expense of attendancebeing of comparatively minor consequence. The quantity of fuel required to produce a stated power depends upon the construction of the engine itself, upon the character of the boiler and its furnace, and lastly npon the skill exercised in firing. In estimating the horse-power of an engine, the old plan of multiplying the number of squale inches of piston surface by the pressure in pounds per inch in the boiler, and dividing the product by thirty-three thousand, should be ignored ; it having been proved fallacious nearly half a ceil, tury ago. Instead of the steam pressure iu the boiler, the steam pressure in the о linder when the piston is in motion mnst be taken as the multiplier of the piston area. De Pambour, many years since, in France, demonstrated that the presaure of steam on the moving piston is frequently only a quarter as much as the boiler pressnre. This diminution of pressure in the cylinder, as compared with that in the stesm-generator, is due partly to bends and impediments in the steam passages, and partly to radiation from the cylinder surface, but in the main to the fact that the steam having to follow the piston is not able to exert its f nil pressure. From this arises the utility of the indicator showing tho steam pressure at all portions of the stroke. For judging a steam cngipc without regard to the kind of boiler used with it, the weight of steam has until very recently furnished the most practical teat, although priming, &c, always makes the apparent evaporation greater than that which really takes place. For trials made on this system, Dr. Van der Weydc gave the fallowing as the rules imperative to be observed, if anything approaching reliable results arc to be obtained by this method.

"1st. The water to be measured in tanks, and not by water-meters, which are always unreliable. 2nd. No steam to be used from the boiler, during the trial, for other purposes than for the engine to be tested. 3rd. To lot the engine perform a constant well-determined amount ot labour during tho trial. 4th. Tho amount of water in the boilers at the end of the experirneut should be exactly the same as in the beginning. 5th. Whon the boilers have blown off salt or muddy water, during tho trial, this amount should be ascertained. Gth. The experiments should bo very carefully and skilfully performed, and often repeated, in order to eliminate incidental inaccuracies, caused by temperature of the air, variation of water-level, &c."

The objections to the above method, familiar to engineers, may be obviated by a more truly scientific one, which consists in recordiug the units ot heat carried off by.the exhaust steam. By simply providing a condensing engine for and specific time witli a deiiuite quantity of water ач a condensing agent, and noting, by means of a thermometer, the degrees of heat coinuiuuicated to it by the condensation of the steam, the quantity of heat carried off by the exhaust may he found by a simple calculation. This has very much facilitated the accurate testing of different rates of expansion, &c. The units of heat thus carried olf iu the exhaust are of course so much abstracted from the foroc employed to drive the piston, and the less this quantity of heat, other conditions being equal, the more efficient the engine lor a given expenditure of fuel. The mode of applying the test is very simple, it being only necessary to place i no thermometer in the inlet of water to the condenser and tho other at the outlet of the latter. By noting the difference in the temperatures indicated by th j two, it remaius only to know the quantity of water passed through the condenser per minute, and the results may be readily

computed. In testing high pressure 01 non-oondensing engines the same principle is applied, but in a somewhat different manner, the exhaust steam being turned into water in a tank of known capacity, so that the rise in temperature for a given time furnishes, as in the previous instance, tbe required data of the heat carried from the engine by the exhaust.

SPECTROSCOPIC OBSERVATIONS OF THE

SUN.«

Br J. Norman Lockyer, F.R.S.

THE weather has lately been fine enough, and the sun high enough, during my available observation time, to enable me to resume work. The crop of new facts is not solarge as it would have been had I been working with a strip of the sun, say fifty miles or a hundred miles wide, instead of one considerably over 1000—indeed, nearer 2000 in width ; but in addition to the new facte obtained, I have very largely strengthened my former observations, so that the many hours I have spent in watching phenomena, now perfectly familiar to me, have not been absolutely lost.

The negative results which I)r. Frankland and myself have obtained in our laboratory-work in the matter of the yellow bright Hoe near D, in the spectrum of the chromosphere being a hydrogen line, led me to make a special series of observations on that line, with a view of differentiating it, if possible, from the line 0.

It had been remarked, some time ago, by Prof. Zollner, that the yellow line was often less high in a prominence than the С line; this, however, is no evidence (bearing in mind our results with regard to magnesium;. The proofs I have now to lay before the Royal Society are of a different order, and are, I take it, conclusive :—

1. With a tangential slit I have seen the yellow line bright below the chromosphere, when the С line has been dark j the two lines being in the same field of view.

2. In the case of a blight prominence over a spot on the disc, the С and F lines have been seen bright, while the yellow line has been invisible.

3. In a high-pressure injection of hydrogen, the motion indicated by change of wave-length has been less in the case of the yellow line than in the case of С and F.

4. In a similar quiescent injection the pressure indicated has been less.

5. In one case the 0 line was seen long and unbroken, while the yellow line was equally Ions but broken. 6'

The circumstance that this line is so rarely seen «lark upon the sun makes me suspect a connection between it and the line at 5015 Angstrom, which is also a bright line, and often is seen bright in the chromosphere, and then higher than the sodium and magnesium lines, when they are visible at the same time ; and the question arises, must we not attribute these lines to a substance which exists at a higher temperature than those mixed with it, and to one of very great levity ? for its absorption-line remains invisible, as a role in spot-spectra.

I have been able to make a series of observations on the fine spot which was visible when I commenced them on April 10th, not far from the rt ntre of its path over the disc. At this time, the >jot, as I judged by the almost entire absence ut indications of general absorption in the penumbral regions, was shallow, and this has happened to many of the spots seen lately. A few hours' observation showed that it was getting deeper apparently, and that the umbra; were enlarging and increasing in number, as if a general downsinking were taking place; but clouds came over, and the observations were interrupted.

By the next day (April 11) the spot had cer tainly developed, and now there was a magnificently bright prominence, completely over the darkest mass or umbra, the prominence being fed from the penumbra or very close to it, a fact indicated by greater brilliancy than in the bright С and F Unes. 6

April 12. The prominence was persistent. April 15. Spot nearing the limb, prominence strll persistent over spot. At 11 I saw no prominence of importance on the limb, but about an hour afterwards I was absolutely startled by a prominence not, I think, depending on the spot I have referred to, but certainly near it, more than

2ft. high, showing a tremendous motion towards
the eye. There were light clonds, which reflected
to me the solar spectrum, and I therefore saw the
black С line at the same time. The prominence
С line (on which changes of wave-length arc not
so well visible as in the F line) was only coinci-
dent with the absorption-line for a few seconds of
arc!

Ten minutes aftei wards the thickness of the
line towards the right was all the indication of
motion I got. In another ten minutes the bright
and dark lines were coincident.

And shortly afterwards what motion there was, was towards the red!

I pointed out to the Royal Society, now more than a year ago,* that the largest prominences, as seen at any one time, are not necessarily those in which either the intensest action or the most rapid change is going on. From the observations made on this and the following day, I think that we may divide prominences into two classes :—

1. Those in which great action is going on, lower vapours being injected ; in the majority of cases these are not high, they last only a short time—are throbs, and are often renewed, and are not seen so frequently near the sun's poles as near the equator. They often accompany spots, but are not limited to them. These are the intensely bright prominences of the American photographs.

2. Those which are perfectly tranquil, so far as wave-length evidence goes. They are often high, are persistent, and not very bright. These do not, as a rule, accompany spots. These are the "radiance" and dull prominences shown in the American photographs.

I now return to my observations of the spot. On the 16th, the last of the many umbrae was close to the limb, and the most violent action was indicated occasionally. I was working with the С line, and certainly never saw such rapid changes of wave-length before. The motion was chiefly horizontal, or nearly so, and this was probably the reason why, in spite of the great action, the prominences, three or four of which were shut out, never rose very high.

I append some drawings, made, at my request, by an artist, Mr. Holiday, who happened to be with me, and who had never, seen my instrument or the solar spectrum widely dispersed before. I attach great importance to them, as they are the untrained observations of a keen judge of foim.

The appearances were at times extraordinary and new to me. The hydrogen shot out rapidly, scintillating as it went, ap.d suddenly here and there the bright line, broad and badly defined, would be pierced, as it were, by a line of intensely brilliant light parallel to the length of thespectrnm, and at times the whole prominence spectrum was built up of bright lines so arranged, indicating that the prominence itself was built up of single dischargee, shot out from the region nearthelimb with a velocity sometimes amounting to 100 miles a second. After this had pone on for a time, the prominence mounted, and the cyclonic motion became evident ¡ for away from the sun, as shown in my sketch, the separate masses were travelling away from the eye ; then gradually a background of less luminous hydrogen was formed moving with various velocities, and on this background i he separate "bombs" (I was working with a vertical spectrum) like exquisitely jewelled ear-rings.

It soon became evident that the region of the chromosphere just behind that in which the prominence arose, was being driven back with a velocity something like 20 miles a second, the back-rush being so local that, with the small image I am unfortunately compelled to use, both tbe moving and rigid portions were included in the thickness of the slit. I saw the two absorbing-lines overlap.

These observations were of great importance to me; for the rapid action enabled me to put together several phenomena I was perfectly familiar with separately, and see their connected meaning. They may be summarised as follows, and it will be seen that they teach us much concerning the nature of prominences. When the air is perfectly tranquil in the neighbonrhood of a large spot, or, indeed, generally in any part of the disc, we вее absorption-lines running along the whole length of the spectrum, crossing the Frauenhofer lines, and they vary in depth of shade and breadth according as we have pore, corrugation, or spot under the corresponding part of the slit—a pore, in fact, is a spot. Here and there, where the spectrum is brightest (where a bright point of

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fácula is under the slit) we suddenly see this appearance—an interesting bright lozenge of light. This I lake to be due to bright hydrogen at a greater pressure than ordinary, and this then is the reason of the intensely bright points seen in ranges of fácula: observed near the limb.

The appearance of this lozenge in the a pectrr scope, which indicates a diminution of p re f -n round its central portion, is the signal for some

and often all, of the following phenomena:

1. A thinning and strange variation in the visibility and thickness of the hydrogen absorption-line under observation.

4. If nearthelimb, this prominence may extend beyond it, and its motion-form will then become more easy of observation. In such cases the motion is cyclonic in the majority of cases, and generally very rapid, and—another feature of a solar storm—the photospheric vapours are torn up with the intensely bright hydrogen, the number of bright lines visible determining the depth from which the vapeurs are torn, and varying almost directly with the amount of motion indicated.

Here, then, we have, I thmk, the chain that connects the prominences with the brighter points of the fáculas.

These lozenge-shaped appearances, which were observed close to the spot on the 16th, were accompanied by the " throbs " of the eruption, to which I have before referred ; while Mr. Holiday was with me—a space of two hours—there were two outbursts, separated by a space of almost rest, and each outburst consisting of a series of dis-' charges, as I have shown. I subsequently witnessed a third outburst The phenomena observed on all three were the same in kind.

On this day I was so anxious to watch the various motion-forms of the hydrogen lines, that I did not use the tangential slit. This I did the next day (the 17th of April) in the same region when similar eruptions were visible, though the' spot was no longer visible.

Judge of my surprise and delight, when upon sweeping along the spectrum, I found hundreds of the Frauenhofer lines beautifully bright at the base of the prominence! 1!

The complication of the chromosphere spectrum was greatest in the regions more refrangible than C, from E to long past 4, and near F, and high pressure iron vapour was one of the chief causes of the phenomenon.

I have before stated to the Royal Society that I have seen the chromosphere full lines; but the fulness then was as emptiness compared with the observation to which I now refer.

A more convincing proof of the theory of the solar constitution, put forward by Dr. Frankland and myself, conld scarcely have been furnished. This observation not only endorses all my former work in this direction, but it tends to show the shallowness of the region on which many of the more important solar phenomena take place, as well as its exact locality. I

The appearance of the F line, with a tangeniai slit at the base of the prominence, included two о the lozenge-shaped brilliant spots to which I have before referred; they were more elongated than usual—an effect of pressure, I hold, greater pressure and therefore greater complication of the chromosphere spectrum; the complication is almost impossible of observation on the disc.

It is noteworthy that in another prominence, on the same side of the sun, although the action was great, the erupted materials were simple, i.e., only sodium and magnesium, and that a moderate alteration of wave-length in these vapours was obvious. Besides these observations on the 17th, I also availed myself of the pnreness of the air to examine telescopically the two spots on the disc, which the spetroscope reported tranquil as to up and down rushes. I saw every cloud-dome in their neighbourhood perfectly, and I saw these domes drawn out, by horizontal currents, doubtless, in the penumbra;, while on the floors of the spots, here and there, were similar cloud-masses, the distribution of which varied from time to time, the spectrum of these masses resembling that of their fellows on the general surface of the sun.

I have before stated that the region of a spot comprised by the penumbras appears to be shallower in the spots I have observed lately (we are now nearing the maximum period of sun spots) ¡- I have further to remark that I have evidence that the chromosphere is also shallower than it was in 1868.

I am now making special observations on these two points, as I consider that manv important conclusions may be drawn from them.'

J

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MECHANICAL MOVEMENTS.*
(Continited from page 292.)

Ш Intermittent rotary motion from • continuous rotary motion about an axis at right angles. Small wheel ou left is driver ; and the friction rollers on its radial etude work against the faces of oblique grooves or projections across the face of the larger wheel, and impart motion thereto.

165. Cylindrical rod arranged between two rollers, the axes of which are oblique to each other. The rotation of the rollers produces both a Iongitnd mal and a rotary motion of the rod.

166. Drilling machine. By the large bevelgear, rotary motion is given to vertical dnll-shaft, which slides through small bevel-gear but is made to turn with it by a feather and groove, and is depressed by treadle connected with upper lever.

167. A parallel ruler with which lines may be drawn at required distances'apart without setting ont. Lower edge of upper blade has a graduated ivory scale, on which the incidence of the outer edge of the brass arc indicates the width between blades.

168. Describing spiral line on a cylinder. The spur-gear which drives the bevel-gears, and thus gives rotary motion to the cylinder, also gears into the toothed rack, and thereby causes the marking point to traverse from end to end of the cylinder.

169. Cycloidal surfaces, causing pendulum to move in cyoloidal curve, rendering oscillations isochronous or equal-timed.

170. Motionfor polishing mirrors, the rubbing of which should be varied as much as practicable. The handle turns the crank to which the long bar and attached rachet-wheel are connected. The mirror ie secured rigidly to the ratchet-wheel. The long bar, which is guided by pins in the lower rail,has both a longitudinal and an oscillating movement and the ratchetwheel is caused to rotate intermittently by a click operated by an cocentrie on the crank-shaft, and hence the mirror has a compound movement.

171. Modification of mangle-wheel motion. The large wheel is toothed on both faces, and an alternating circular motion is produced by the uniform revolution of the pinion, which passes from one side of the wheel to the other through an opening on the left of the figure.

172. White's dynamometer, for determining the amount of power required to give rotary motion to any piece of mechanism. The two horiiortal bevel-gears are arranged in a hoop-shaped frame, which revolves freely on the middle of the horizontal shal, on which there are two vertical

MECHANICAL MOVEMENTS.

level-gears gearing to tho horizontal ones, one fast and the oiher loose on the shaft. Suppose the hoop to be held stationary, motion given to either vertical bevel-gear will be imparted through the horizontal gears to the other vertical one: but if the hoop be permitted it will revolve with the vertical gear put in motion, and the amonnt of power required to hold it stationary will correspond with that transmitted from the first gear, and a band attached to its periphery will indicate that power by the weight required to keep it still.

173. Robert's contrivance for proving that friction of a wheel carriage does not increase with velocity, but only with load. Loaded waggon is supported on surface of large wheel, and connected with indicator constructed with spiral spring, to show force required to keep carriage stationary when large wheel is put in motion. It was found that difference in velocity produced no variation in the indicator, but difference in weight immediately did so.

174. Rotary motion of shaft from treadle by means of an endless band running from a roller on the treadle to an eccentric on the shaft.

175. Pair of edge runners or chasers for crushing or grinding. Tho axles are connected with vertical shaft, and the wheels or chasers run in an annular pan or trongh.

170. Tread-wheel horse-power turned by the weight of an animal attempting to walk up one side of its interior ; has been used for driving the paddle-wheels of ferry-boats and other purposes by horsjs. The turnspit dog used also to be employed in such a wheel in ancient times for turning meat while rsasting on a spit.

177. The tread-mill employed in gaols in some countries for exercising criminals condemned to labour, and employed in grinding grain, &c; turned by weight of persons stepping on tread-boards on periphery. This is supposed to be a Chinese invention, and is still used in China for raising water for irrigation.

178. Saw for cutting trees by motion of pendulum, is represented as cutting a lying tree.

(To be continued.J

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EXHIBITION OF 1871.

THE year 1871 will вес the first of a series of annual InternationalKxhibitions, which while formed on such basis as experience gained by the many exhibitions that have been held during the last; twenty years has shown to be right and desirable, are yet due to, and actually spring from, the success of Che great Universal Exhibition of 1851. The close of that undertaking found the Commissioners incorporated to carry it ont possessed of a surplus amounting, in round numbers, to £180,000. This surplus the Commissioners

bound themselves by charter to deal with according to the spirit in which the Exhibition had been conceivod, and the object for which the publio money had been asked for and received—that i«, in the encouragement of artand industry. It was therefore invested in such a manner as should render it available, at some future time, for the establishment of permanent exhibitions.

That time has now arrived, and the series that commences next year is therefore the direct result of the Exhibition of 1851, and the Commissioners intend to bear the whole cost and responsibility, without either government money or public guarantee.

Permanent exhibitions must of necessity be established on a different basis than those which are temporary, if they are to be successful. The promoters of the Exhibition of 1851 had no stitistics by which they could be guided iuto the right course of action. The many exhibition* that have, however, been held since in this und other countries have afforded proof that there are certain limits of time, space, and expense which cannot be exceeded without loss and failure. To hold them at any other period than between the months of May and September, is practically to shut out many of the productions of Northern Europe, where the ports are closed by the rigours of winter. The expense of the erection of temporary buildings for decennial exhibitions was constantly increasing, and, with other charges, rendered it necessary for those who undertook their promotion to incur a heavy pecuniary liability, which, coupled with the limits as to the time during which the exhibition could remain open, rendered financial success, at each succeeding exhibition, more difficult of attainment.

Generally, the exhibitions outgrew their limits. For the fulfilment of their legitimate purpose, which was to show from time to time the progress made by artand industry, in connection with the staple manufactures of the country in which they were held, necessitated that a largo number of objects should be received, required enormous space for their exhibition, though in themselves possessing but little merit as objects of artistic industry.

With these facts before them, the Commissioners propose, in the first place to make an International Exhibition a permanent institution of that country, giving to the industrial art the sama opportun i y that is afforded to fine art by the annual exhibitions of the Royal Academy. In thai second place, they propose to reduce thearca over) which the exhibition shall spread itself, by reducing the various industries into groups, and taking certain of these each year, bring the entire^ indu,try of the country under review every sever or eight years, fine art being a standing diviaio;

of the programn e. And, in the third place, to restrict the conditions under which exhibits have hitherto been received, by making all articles undergo a preliminary sifting, through appointed committees of selection, thus excluding all works that do not possess sufficient artistic merit to warrant their exhibition, and by the further exclusion of mere masses of natural products.

The great aim of the early periodical exhibition« established by the Society of Arts was the closer union of art and industry ; this was also the object which II.liH. tbe Prince Consort had so much at heart in promoting the first Great Exhibition. The Commissioners now propose, in those permanent exhibitions, to carry on the work of bringing about a closer alliance between artistic design and usefulness of purpose, by, to use their own words, " stimulating the application of the artists' talon tí, to give beauty and refinement to every description of object of utility."

REVIEWS.

"The Modern Practical Angler: A Complete Guide to Fly-fishing, Bottom-fishing, and Trolling." By II. Cholmoniielby-pen.nell, Inspector of Fisheries. Author of the " AnglerNaturalist," the "Book of the Pike," &o. London : P. Warne and Co.

"\\7 E imagine that most of our readers who '* have any pretensions to be considered fishermen, or who have followed the windings of any of our beautiful streams in search of the pleasure which Angliog affords alike to the greatest statesmen as to the meanest kind, will not require to be told that Mr. Pennell is one of our most accomplished anglers, whether in theory or practice. Those who have read his "Book of the Pike" well know the amount of information he las brought to light concerning the habits and peculiarities of the "pirate of the river"— indeed, so carefully and minutely has he described the life-history of this fish, that he is commonly called the "Father of Pike-fishers." We offer no apology, therefore, for plunging at once into the mysteries of the craft, convinced that what Mr. Pennell recommends, however novel, is at all events worth trial; and аз the holidays are drawing near, we will see what he has to say towards filling the creels of such of our readers as may betake them to the Tweed, the Blackwater, or the Thames.

The author commences his manual by saying that pike and trout, like other mundane creatures, are better educated, or at all events sharper, than their progenitors of the time of bask Walton or Dame Juliana Berners, who wrote the "Boke oí St. Alban's," published about 1486, wherein the rod is recommended to be of at least some lift. 'dong ; the "stage " or butt, measuring a ," fadooin (fathom) and a-half," of the thickness of an "arra-gretc,-' or about as thick as a man's arm, the joints being bound with long "hopis of yren" (iron hoops). But whether fish are more intelligent, or are simply more timid, from their inability to find in the United Kingdom a mile of water that is not haunted by those tantalising tlios that have wrought the doom of so many of their comrades, Mr. Pennell is decidedly and emphatically of opinion that the man who fishes "finest" will be able to show the heaviest creel at tho close of a day's sport.

Chapter I. lays down the theory of what a book should be, describes the various forms of hooks ntherto used, »nd alter pointing out their numerous deficiencies, explains the advantages of Mr. Pennell's pattern, which has all the good qualities of the "suck" and "eproat-bend," without their drawbacks. It much resembles the 'eneck," but with a difference in bond, as well is in the barb and point, and is certainly much stronger, because the strain is distributed, and loes not fall on one part. The author has, also, loviaed a new form of the rather-important 'lip-hook," on which depends the proper posiion of the bait and flight. By leaving the shank at the hook unpolished, and altering the position if the loops so that the line lies close to the hook, le has succeeded in obtaining the requisite ease n shifting, and fixity when required, combined litU durability and neatness.

Iu the matter of spinning tackle Mr. Pennell pouks with no uncertain voice. He unhesiatingly condems the employment of such a

number of triangles and hoots, as was formerly the fashion—sometimes no fewer than three to five of the former being used on one flight—and he attributes to them, and to the "crinkling " or "kinking" of the line, the loss of about 50 or CO per cent, of fish after being struck. Here are his own words :—" These [triangles] were not only useless, but distinctly mischievous, both as regards the spinning of the bait and the basketing of tho fish when hooked. Upon the bait they acted by impairing its brilliancy and attractiveness, rendering it flabby and inelastic. Upon the fish they operated only as fulcrums, by which he was enabled to work out of the hold of such hooks as were already fast. The great size and defective bends of many of the hooks used, contributed materially to swell the proportion of losses, as it should be remembered that to strike a No. 20 hook fairly over the barb, requires at least three times the force that is required to strike in a No. 10; and that this disparity is increased when the hooks are used in triangles. A jack, say, has taken a spinning-bait dressed with a flight of three or four of these large triangles, and a sprinkling of single hooks—perhaps 11 or 12 in all. The bait probably lies between his jaws, grasped crosswise, and therefore tho points of at least six of these hooks will be pressed by the fish's mouth, whilst the bait also to which they are attached is held firmly in, his teeth. The whole of this combined resistance must be overcome—and that at one stroke, and sharply— before a single point can be buried above " the barb."

In the matter of "kinking," Mr. Pennell has inquired into what might be called the science of the subject; and instead of passing his tract through the centre of the weight, in which position the lead could not, of course, prevent the line from turning, he fastens the lead to the side of the line, or, at least, in such a position that nearly the whole weight is exerted against the twisting of the line. He recommends that the lead should be varnished with powdered dark-green sealing-wax, mixed with spirits of wine to the consistency of thin treacle. With the lead fixed in this manner ore really good swivel will be found sufficient, although a double one avoids any hitch that might arise through the single swivel being rusty. Speaking of trollinglines, the author is decidedly opposed to hair, when used by itself (when a Hue 80 yards long would cost Ms. or 30s.), or mixed with silk; but recommends the use of what is known as 8-plait dressed silk, of a pale green tint.

For reel-lines for fly-fishing, Mr. Pennell, till within the past twelvemonths, has used the dressed silk; but bi has recently tried a line made of spun cotton, which, while much cheaper than the dressed silk, is equally strong and more durable. It is " cable-laid "—i.e., the " ropes " of which the cable is made arc twisted tho reverse of the strands, aud the twisting of the " cable " is the opposite of the "ropes." Mr. Pennell speaks highly of these lines, and says they "answer perfectly, both for fly-fishing and ordinary bottom fishing."

For bottom-fishing and fly-fishing lines gut is to be preferred—the fine, round, natural gut, that is not scraped, and made small artificially, and consequently weaker.

Mr. Pennell next describes the various woods used in the manufacture of rods, and the processes they undergo before they appear as the perfect implement. He prefers as a general rule, rods with ash bntts, and middle, and tops made of greenlmrt (? g reo n h tart), and, what will surprise most readers, says, that the difference in weight between rods of solid wood and those made of bamboo, is so trifling, as scarcely to be worthy of consideration :—"I weighed a 12ft. solid ash and grcenhart trolling-rod, against one of stout East India bamboo, and the weights were:—solid rod lib. 0,'oz., hollow rod lib. 4oz.; difference, ljoz." The knots used in fastening lines and hooks are elaborately described, and being illustrated, are made plain to the merest tyro.

It would take a whole chapter to thoroughly examine Mr. Pennell's theory of flies and flyfishing ; and we must be content to state that, instead of expatiating on the allurements and beauties of the "thousand and one " flies to be »cell in tiiokle-Bhops, he is convinced that six typical ones are all that is necessary for the purposes of the angler, no matter what water he is fishing—three being devoted to salmon aud grilse, and three to trout, grayling, eke Mr. Pennell is opposed to fishing up-stream, except when a

strong wind is blowing in that direction, and as most experienced anglers are of his way of thinking, there cannot be much doubt that he is correct, especially as this method is found to fail in practice. The author likewise advises—what will be considered rank heresy by some—that in¿ spinning for pike the fisherman should strike directly he feeU a run. But we have limits t» our space, and most conclude by observing that the remaining chapters of Mr. Pennell's hook, containing a description of tie different varieties of fish, their habits and their haunts, together with the method of angling for them, and the best kinds of tackle to use m endeavouring to achieve their capture. There are also some excellent lithographs, which really represent the fish they are intended for, and there is a coloured frontispiece representing the flies the author considers sufficient for all practical purposes. We may have occasion to refer to this work again, but in the mean time we are confident that while the fisherman who is a proficient in his art will find much to claim his attention, it is a very vade-meoum for all tyros who wish to become masters of the "gentle craft."

"Drawing for Carpenters and Joiners, &c, &c." By Ellis A. Davidson. Cassell, Petter, and Galpin.

We have on three previous occasions drawn attention to the very cheap and good technical manuals by Mr. Ellis A. Davidson, recently published by Messrs. Cassell, Petter, and Galpin. The present volume is thoroughly worthy of its predecessor on "Building Construction," and should reach a far wider circle. All of us are, or think ourselves more or less carpenters, and the more or less miserable specimens of the art some amateurs occasionally turn out, should serve to remind them of the necessity of their possessing a book like the one beforo us. If one thing is more certain than another it is that good execution must be preceded by good design, and a carpenter unable to use his pencil labours nnder terrible disadvantages. "Drawing," as Mr. Davidson most truly says, "is the language of the workshop more eloquent than words, more rapidly understood, and less liable to be misapprehended." The book is so arranged as to combine linear, freehand, and object drawings each of these branches being again divided and subdivided, and thus in linear drawing, foundations, piles, cofferdams, wooden bridges, roofs, staircases, doors, gates, &c, are made subjects of study. Mouldings, borders, scrolls, &c, are included in the freehand section; whilst under the head of object drawing, a few simple rules of perspective and shading are given, in order to enable the student to draw with some degree of correctness from the subject before him.

"The Second Course of Orthographic Projection being a Consummation of the New Method of Teaching the Science of Mechanical and Engineering Drawing," &eek. By William Binns, Ass. I.C.E. London: E. and F. N. íípon, 48, Charing-cross.

THEeuccess of the author's elementary treatise on "Orthographic Projection and its Application to Mechanical and Engineering Drawing," confirmed his intention of hereafter publishing a larger and more comprehensive work, although he appears to have delayed it very considerably on account of the pertinacious efforts of "men who have had no practice in the workshop," to "put it down." It would undoubtedly have been a loss to those for whom the publication is intended, had its appearance been altogether prevented. It is an exceedingly useful book, not only for the mechanical draughtsman, who will find in it a perfect encyclopaedia of "wrinkles" and dodges to aid him in the easy accomplishment of his work, but by;engineers and patternmakers, a considerable portion of the space being devoted to a subject in constant discussion among our readers—the formation of the teeth of wheels. Mr. Binns claims, without materially altering the form of tooth acknowledged to be the best, to have introduced one that shall be uniform, thus avoiding the anomalous practice which still exists in this important branch of mechanical engineering.

Mr. Binns' method of teaching mechanical drawing is now practised in the various art schools of the United Kingdom, and we have little doubt that this record of its publication will be gladly

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