to reveal them. to absolute demonstration; for, however cleansed in appearance, a stubborn objector might still urge that the air was not cleansed in reality; that germs exist though they baffle our attempts But this difficulty does not hamper the other side; for if, notwithstanding the risk of these residual germs, "visibly pure air" can be proved incompetent to produce the phenomena of putrefaction, there is no escape from the inference that, as regards the point to be decided, such air is perfectly filtered; and its proved impotence would be a demonstration of the truth of the germ theory. By "visibly pure air" I mean air which, where traversed by a powerful and intensely-concentrated beam of light in a space not otherwise illuminated, reveals no trace of floating matter to the eye. How, then, are we to obtain our filtered air, and, having obtained it, how are we to apply it to a wound and mix it effectually with the blood? Two or three years ago an observation and an inference, which, taken together, reflect the highest credit on his sagacity, were made and drawn by Professor Joseph Lister, of Edinburgh. He found, and I believe it is the universal experience of surgery to find, that when the lung is wounded by the spike of a broken rib, air from the pleural cavity may mingle freely with the blood, but that putrefaction never ensues. Here is the statement of Professor Lister, abbreviated, but in his own words :-"I have explained to my own mind the remarkable fact that in simple fractures of the ribs, if the lung be penetrated by a fragment, the blood effused into the pleural cavity, though freely mixed with air, undergoes no decomposition. The air is some times pumped into the pleural cavity in such abundance that, making its way through the wound, it inflates the cellular tissue of the whole body. Yet this occasions (as regards putrefaction) no alarm to the surgeon. Why air introduced into the pleural cavity through a wounded lung should have such wholly different effects from that entering through a permanently open wound penetrating from without, was to me a complete mystery till I heard of the germ theory of putrefaction, when it at once occurred to me that it was only natural that the air should be filtered of germs by the air passages, one of whose offices is to arrest inhaled particles of dust, and prevent them from entering the air-cells. In truth this fact in practical surgery, when duly considered, affords as good evidence in support of the germ theory of putrefaction as any experiment that can be formed artificially." no matter would open a highway for the, animalcule PROBABILITIES IN SCIENCE. We do not know and in their physical state." under the dominion of forces incomparably more ALL science depends upon the probability of the results. In many cases our minds are strongly influenced by the variety, as well as by the quantity of the facts which a given theory coordinates in that particular manner to which we apply the term explanation. Thus, in the case of light, the capability of the undulatory theory to explain phenomena of polarisation and diffraction, as well as those of reflexion and refraction, adds much to its credibility. a tion of nebulæ. An indication of incandescent hydrogen, for example, obtained by such means, is not quite conclusive, and it is, in the present state of knowledge, impossible to ascertain exactly what it is worth. An experimenter wishing to obtain a spectrum of incandescent hydrogen operates with a coil machine and a Geissler tube. He makes the rarefied gas luminous by a powerful electric discharge, which strongly heats it, and in comparing his results with those obtained with the light fi om First, we have nebula, two suggestions occur. no evidence that the luminous nebula is intensely heated, by any internal action, or by any external force. In the next place we know scarcely anything about the density of the matter that composes it. At first it would seem that if highly In like manner, the nebular hypothesis has heated hydrogen gave a particular spectrum in the laboratory experiment, it was highly improgrown in probability by a succession of dis-bable that exactly the same spectrum should appear coveries and observations which are found consistent with it; but there is at present so much that remains unaccounted for, that we may be justified in thinking that this theory will have to be modified, as well as completed, before it can reach the degree of probability attained by the undulatory theory of light. know, some interesting speculations on this subject, which we hope he will work out. Mr. Proctor has, we Here is a surmise which bears upon it the mark of genius, but which nevertheless needs verification. If in the place of the words it is only natural," we were authorised to write "it is perfectly certain," the demonstration would be complete. Now, this is exactly what experiments with a beam of light enable us to do. One evenIn all speculations on the condition of highly ing towards the close of last year, while pouring various gases across the dusk track of a beam in attenuated matter, such as nebula, or comets, the laboratory of the Royal Institution, the swimming in the cold and rare fluid that occupies thought occurred to me of displacing by my the regions of space, we are under great diffibreath the illuminated dusk. I then noticed for culties from want of analogies to help us. The the first time the extraordinary darkness produced matter of cemets is in a condition not like any by the air expired towards the end of an expira- thing we are acquainted with in some important tion. By an intentional effort of expulsion the particulars. Sir John Herschel says, "It is evilungs may be far more effectually emptied of air dent that the most unsubstantial clouds which than by ordinary respiration; and by such an float in the highest regions of our atmosphere, effort, which discharges the air from the interior and seen at sunset to be drenched in light, and portion of the lungs into the beam, the darkness to glow throughout their whole depth as if in is changed to absolute blackness. There is actual ignition, without any shadow, or dark side, speck or mote of any kind in such air. It is a must be looked upon as dense and massive true elastic fluid, without a trace of cloud or bodies compared with the filmy, and all but floating matter. Thus, by ocular evidence we spiritual texture of a comet." In 1767, Lexell's prove the filtering power of the lungs, and by comet approached Jupiter, by whose attraction the experience of surgery we prove the incom- its orbit was materially changed, but its mass was petence of air so filtered to produce putrefaction. so small that it was not able to produce any The germs removed by the process of filtration noticeable disturbances in the little bodies of the are therefore the cause of the putrefaction, and great planet satellites. its associated phenomena of animalcule life, which Cometary matter does not appear to be in one was to be demonstrated. As a guide to the state only. Sir J. Herschel says of comets :-" In practical surgeon, the establishment of this fact all probability they admit of great varieties of is plainly of the very highest importance. Pro- structure, and among them may very possibly be fessor Lister now avails himself of the filtering bodies of widely different physical constitution power of cotton wool in treating a numerous class and there is no doubt that one and the same different epochs, undergoes great of wounds. He first destroys the germs adherent comet, at to the wool, and by a proper lotion he kills those changes, both in the disposition of its materials, which may be scattered on the flesh. The The black wreaths produced by placing the flame cleansed wool placed upon the wounds permits of of a spirit lamp underneath the track of a sunbeam a free diffusion of the air, but entirely intercepts may now be clearly though imperfectly seen in every The light, save that passthe germs, and thus keeps the blood perfectly drawing-room in London. sweet. It is essential that no matter from the to be excluded. A candie flame also shows the effect, ing through a single aperture, ought, as far as possible, wound should reach the outside air, for such but very imperfectly. except similarly heated hydrogen were its canse. The amount of improbability of accidental coincidence is enormously great-great enough to be discarded. From a moderately extensive range of experiments we know that a considerable number of the bodies which we call simple," simply because we cannot, or have not decomposed them, afford, in the state of incanthis it is inferred that this rule holds good under descent vapour, characteristic spectra, and from all circumstances. Certain facts in the spectra of gases raise some doubts, but it must be admitted that a powerful probability is established that certain nebula are composed of luminous, if not of incandescent† gaseous matter, to which the term incandescent is commonly applied, though before we know how to estimate the value of this probability we must see what other probabilities are raised by the same or other researches. On making his most important examination of a nebula in Draco, Mr. Huggins saw three isolated bright lines, instead of the continuous spectra given by stars, and he said, "A spectrum of this character, so far as our knowledge at present extends, can be produced only by light which has emanated from matter in the state of gas. light of this nebula, therefore, was not emitted from incandescent solid or liquid matter, as is the light of the sun and stars, but from glowing or luminous gas." The On comparing the spectrum of nitrogen with that of the nebula, Mr. Huggins says, "I found "An apparent exception to the law that the nature of the spectrum of a gas remains constant throughout a great temperature range ought to be remarked in the case of nitrogen, which changes the nature of its spectrum at a very high temperature. This is viewed by some as an indication that nitrogen is really a compound body, since the same change takes place in the spectra of some other gases, which Elementary Treatise on Heat." we know to be compound."-Balfour Stewart, "An Plücker has made important observations on this subjcet. + Incandescent properly means being made white by heat. that the brightest of the lines of the nebula coincided with the strongest of the lines that are peculiar to nitrogen. It may be, therefore, that the occurrence of this one line only indicates a form of matter more elementary than nitrogen, and which our analysis has not yet enabled us to detect. In a similar manner the faintest of the lines was found to coincide with the green line of hydrogen." He adds, "The middle of the three lines which form the spectrum of the nebula does not coincide with a very strong light in the spectra of about twenty of the terrestrial elements. It is not far from the line of barium, but does not coincide with it." A minute nucleus of this nebula appeared to be the source from whence a faint continuous spectrum was obtained, and thence it was inferred to consists of opaque matter, which may exist in the form of an incandescent fog of solid or liquid particles." The comet of 1866 afforded a continuous spectrum from its coma, indicating that it was visible by reflecting solar light; but the nucleus was self-luminous, and gave a gaseous spectrum, "suggesting that the material of the comet was similar to the matter of which gaseous nebulæ consist." It is difficult to suppose that such thin bodies as comets and nebulæ can keep themselves very warm in the intense cold of space. From Professor Tyndall's researches, it appears that oxygen, nitrogen, air (which is a mixture of them), and hydrogen possess very feeble powers both of radiation and absorption. A heated mass of these gases would cool slowly from radiation, but a cold mass would be very difficult to warm by absorption of heat radiated from any other body. MECHANICAL MOVEMENTS. statements we usually receive, and according to posing metals, and certain gases, or carbon, who can venture to predict what fresh spectra may appear? 31 MECHANICAL MOVEMENTS.* motion. Circular motion is PRAGLINK FOL one crank to another. 32. Intermittent circular motion is imparted to the toothed wheel by vibrating the arm B. When the arm, B, is lifted, the pawl, C, is raised from between the teeth of the wheel, and travelling backwards over the circumference, again drops between two teeth on lowering the arm, and draws with it the wheel. 33. Shows two different kinds of stops for a lantern-wheel. 34. Represents a verge escapement. On oscillating the spindle, S, the crown-wheel has an intermittent rotary motion. When we consider comets, how are we to be guided in guessing their temperature? The comet of 1843 went so near the sun as to be exposed to 47,000 such suns' heat as we experience the warmth of, and Sir J. Herschel, from whom we take this statement, observes that the heat emitted by the sun in such a position would be equal to three-and-a-half times that obtained with Parker's great lens, thirty-two and a half inches in diameter, when used with a concentrating lens, increasing its power sevenfold, and melting carnelian, agate, and rock crystal with the solar rays. The actual temperature of the matter exposed to this solar glare and glow would depend upon its nature. If very transparent to heat, it would let much through and retain little. If the heat excited other actions, such as great expansion, or other internal work, all so employed, would not raise its temperature. Many comets seem to grow smaller as they approach the sun, and this has been supposed to arise from portions being converted into a more attenuated and invisible 36. A nearly continuous circular motion is condition. As they recede from the sun they have been observed to get visibly bigger-probably imparted to the ratchet-wheel on vibrating the from condensation. If cometary or nebulous gas lever, a, to which are attached the two pawls, b, passes from a condition the same as or like what we call simple gases, to that of compound gases, its powers of absorption and radiation would, according to Tyndall's researches, be enormously increased. 35. The oscillation of the tappet-arm produces an intermittent rotary motion of the ratchet-wheel. The small spring at the bottom of the tappet-arm keeps the tappet in the position shown in the drawing as the arm rises, yet allows it to pass the teeth on the return motion. and c. 37. A reciprocating circular motion of the top arm makes its attached pawl produce an intermittent circular motion of the crown-ratchet or rag-wheel. 38. An escapement. D is the escape-wheel, and C and B the pallets. A is the axis of the pallets. 39. An arrangement of stops for a spur-gear. 40. Represents varieties of stops for a ratchetwheel. 41. Intermittent circular motion is imparted to the wheel, A, by the continuous circular motion of the smaller wheel with one tooth. To retain nebula or comets in a state of incandescence from heat would require conditions that we Professor Tyndall, in his "Heat as a Mode of do not know to exist. No one, we suppose, would Motion," affirms that the chances that iron is in imagine that heat, radiated from any other body, the sun are 1,000,000,000,000,000,000 to 1, on could keep a nebula white hot, and matter in so account of the coincidence of certain dark lines in rarefied a state is not under favourable circum- its spectrum with certain bright lines yielded when stances for violent chemical actions, such as we incandescent vapour of iron is employed as the know produce great elevation of temperature. source of light. This is put forth as an actual We may, however, have recourse to that refuge calculation. It may be actual in the sense that for those destitute of accurate information-elec- Professor Tyndall actually made it, but purely tricity, and assume that the nebulous glow which imaginary at the same time. The elements for acts upon our spectroscopes comes from electric a real calculation of the probabilities are not excitation. But if this be so, we have gaseous known. Very likely the professor is right if he matter not heated to incandescence giving the thinks only of coincidence arising from chance, same spectrum as gaseous matter that is so heated but we have no information whatever concerning in our laboratory experiments; and before we can the probabilities that coincidences may result from tell the probabilities of the inferences usually law. The quantity of experiments yet made is drawn from the spectra of comets and nebulæ, insufficient to justify such extravagant assertions, 44. A dynamometer, or instrument used for we must ascertain that the same gaseous matter and no one has yet arrived at a law explaining ascertaining the amount of useful effect given in these two conditions would give the same why the spectra of different so-called simple out by any motive-power. It is used as follows: spectroscopic results. Any probabilities that bodies vary exactly as is found to be the case. No-A is a smoothly-turned pulley, secured on a nebulous matters are not incandescent from heat philosopher really imagines that there are scores are probabilities that the laws of luminous spec-of substances which are really simple, and if, as is 42. A brake used in cranes and hoisting machines. By pulling down the end of the lever, the ends of the brake-strap are drawn towards each other, and the strap tightened on the brakewheel. 43. Represents a mode of transmitting power from a horizontal shaft to two vertical ones by means of pulleys and a band. Extracted from a compilation by Mr. H. J. Brown, tra are not so simple as to be comprised in the probable, the chemist may find means of decom-Editor of the American Artisan. APRIL 22, 1870.] shaft as near as possible to the motive-power. 45. Bayonet joint. On turning the part, A, it is released from the L-shaped slot in the socket, B, when it can be withdrawn. (To be Continued.) made into cylinder, it will go much farther; into the shaft S a number of light weights (a, b, &c.), FIG. 10 B s! a SCIENCE FOR THE YOUNG. BY THE REV. E. KERNAN, CLONGOWES COLLEGE. (Continued from page 80.) § III-INERTIA. HE indifference to a change of state of motion or rest, which is observed in bodies, is called Inertia. This property is of considerable importance, both theoretical and practical. Hence, in full form, No. I.-Laws.-Here, and elsewhere later on, may be found laid down as laws what do not deserve strictly to be called such. They are put under that title that they may be more marked, more attended to, and better appreciated. The same reason may be given for detail of Laws, the dividing into two or three what might be in one. The first sentence of these laws will usually contain the law; the rest is but explanation. Law I. All bodies are indifferent to a change from rest to motion. Solids, liquids, gases, will remain at rest for ever, if not forced to change that state by some cause; external cause, as explained in the definition of Mechanics. II. All bodies are indifferent to a change from motion to rest. Solids, liquids, gases, if once set in motion, will never cease to move without the action of some external force, which sooner or later reduces them to a state of rest. III. Time is required to overcome the inertia of a body, whether at rest or in motion. When force is applied to a body a certain amount of time is necessary for the production of the effect of motion or rest. When this time is not allowed, the body acts as if fixed-immovable. IV. The time required varies directly as the quantity of matter in the body. As the body to be moved or stopped has more or less matter, it will require more or less time to change its state. No. II.-Proofs.-These are separated from the laws for several reasons; that the laws may be more easily found; that they may be more evident, short, concise; that the student, with but little time, may know what he can pass over with less disadvantage. Should he be compelled to omit the proofs, he is sure that no principle has been neglected or omitted. Law I. This law is so self-evident that it requires no proof. In fact, the experience of the youngest teaches that where a body is laid there it will stay for ever, unless some force affect its state of rest. of vane mills, mounted on delicate axes, provided on, III. The force applied to a body at rest or in motion must transmit itself from particle to particle of that body. This transmission can only be effected in consecutive moments of time. When there is not sufficient time, those particles which have not received the force resist, as would a mountain. This can be shown by a simple experiment, Fig. 11. A small weight A is laid on thread is broken. IV. This law is clearly a necessary consequence of Law III.; more particles, more time must be given to communicate motion or rest The same experimental proof as in Law III., by using weights of different quantity. With heavy ones, the least increase of rapidity, or stoppage, will cause a breaking of the thread. No. III. Applications.-Under this hord are introduced facts, ordinary and extraordinary, natural phenomena; machines, &c., &c., the explanation of which depends upon the matter just explained. The passing reader may feel inclined to pronounce some of these trivial, unworthy of scien FIC.13 a table. A thread joined to the weight is taken II. Bodies in motion, like those at rest, have in the hand. Raise the weight slowly, the thread nothing in themselves which can effect a change is not broken (a); try to raise the weight with of state. To prove this law experimentally a sudden jerk, the thread breaks. There was not strictly, it would be necessary to solve the im- time for the motion to communicate itself to all possible problem of perpetual motion. Still it the particles of the weight they resisted; the can be very well proved that it is the action of thread might as well have been joined to the tific notice. Such is not the case; the simples external forces which prevents the continuous table or floor. For motion, pass a thread over toy is raised to the dignity of a scientific instru duration of motion once imparted. Thus a square ment when its action is explained on true scien tific principles. Again, the applications may be block of iron, even with considerable force, will move but a short way on a table. Let it be considered at times too multiplied. The effect of the pulley A, Fig. 12, draw up the weight B to 106 this multiplication of common facts explained is to produce a spirit of inquiry than which nothing serves better to foster and develop scientific talent. Application I. The dog and hare, Fig. 13. The hare gradually gathers itself in, to turn. The dog cannot turn-cannot overcome the inertia of his heavier body so quickly. The time he requires is gain to the hare. Other principles, even stronger against the dog, will be seen in their own place. TWO (To be continued.) HIGH-PRESSURE ENGINES. Thames Haven at 3:38, and the run back was colours, rubbing a few on the palette as a stock, WI SKETCHING FROM NATURE. BY SUNSHINE. ITH the permission of our Editor, I now rcsume the pen for a last brief paper upon the above art, just to pick up a few stray not es dropped by the way. Since my last, the spring (Illustrated on page 109.) has really dawned, and the time for practical outWO generations (says the Engineer) have all door work has almost arrived, but, except for but passed away since Jacob Perkins preached artists of strong constitution, a little delay is still the gospel of high-pressure steam-high-pressure advisable, for the treacherous east wind is apt to above and beyond any high-pressure with which creep stealthily over the tenderest parts of the modern engineers have to do. We think it some- body, doing no slight mischief, while the bright thing to boast of that the engines of the North London Railway use steam of 160lb. pressure; sun makes a pretenee (and a pretence only), but Jacob Perkins proposed to use steam of of counteracting its baneful influence. Το 1000lb., and actually did use it under certain those who are not provided with the necescircumstances. The great body of mechanical sary materials for outdoor sketching, engineers labour under the impression that Jacob inclined to recommend the moist colour tu be I am Perkins' ideas died with him. No notion could boxes, Fig. A, which contain a dozen colours be more erroneous. His ideas live with his grand- and folding palette, in preference to the moist carpet with a waterproof lining, for instauce) is open pans. FIC A Certain colours in son, and we saw them in practical application on Wednesday week on board the steam-tug Filga, the property of Mr. Henwood. On board this boat, we confess that we stood for the first time over a marine boiler carrying 200lb. of steam.. Time and space alike forbid us to enter into details. It must suffice to say that the boiler consists of a great number of wrought iron tubes, about 3in. diameter outside, and varying in length from 12ft. to 10ft., within which the water is contained, and round which the heat plays. The engines of the Filga are illustrated, as far as general arrangement is concerned, in the annexed engraving. They were designed by Messrs. Perkins, and constructed by Messre. Hodge, and consist of four colours in cylinders, arranged steam-hammer fashion. The two upper cylinders are high-pressure, 15in. in both are too apt to dry, especially the brown diameter. The low-pressure cylinders are imme- madder and burnt sienna, but the tubes diately beneath them. They are 32in. diameter, protect their contents more completely from the stroke of both being only 1ft. The valves are atmospheric influence. These colours are used all of the double-beat Cornish type, raised from after the manner of oils, a small portion of those their seats by spindles driven by eccentrics, but likely to be needed being squeezed out on a row dropped by the pressure of the steam acting on the plus area of one valve. The surface con- on the upper edge of the white palette, and the densers are of a peculiar construction, of which brush, dipped in water (contained in we shall have more to say. The circulating water attached to the palette), is applied to each as rea cup is driven through it by a pump worked by an quired, compound colours being mixed on a The Filga is of the ordinary Thames screw-tug separate part to the tint required. The advantage type, and it is doubtful if engines of any other of tube boxes is, that it is impossible to spoil form of 80-horse power nominal could have been pure colours by accidental admixture with others. got into her. She is 70ft. long, 14ft. beam, and The brush, dipped alternately into the open pans, in draws 10ft. She has a three-bladed common pro- the other kind of boxes, carries colour from one peller 9ft. 6in. diameter, and 12ft. 6in. pitch. The to another, sullying the whole, as is evident on boiler has not less than 2200 square feet of heating surface, the grate surface being but 30ft. The inspection of any such box freely and often used. estimated consumption is a little under 2ib. of Indeed, I have hardly ever seen a pan box in coal per horse per hour, but the actual consump- which the colours were pure as when first sent tion appears to be much less. On this point we from the maker's, and purity of colour is to be shall have something more to say. The engine considered in all cases one of the essentials of illustrated in the annexed engraving is almost precisely the same as that of the Filga, the only success to be constantly aimed at. To facilitate difference being that the cold water circulating finding the right tube at at a moment's notice, I pump is arranged vertically outside the engine find it a good plan to colour the labels with the frame instead of horizontally, as shown at the left same paint which they respectively contain. of the cut. The Filga left Blackwall on Wednes- Barnard attaches such coloured labels to his oil day, the 6th inst., for a run down the river. The tube colours (I've not seen his water colours), trip was in no sense a trial trip; it was simply and I have found it a great convenience, as in intended to prove to a select body of engineers that it was possible to work 180lb. steam at sea, an oil colour box, one has often a long hunt and, so far, it was completely successful. Steam for a required tube, which may have been was easily maintained throughout the trip at 150lb. several times overlooked in the search. to 190lb. No trace of steam was to be seen about those in possession of colour boxes with pans, I engine or boiler, because the joints are absolutely do not reccommend a change, as many prefer eccentric on the screw shaft. To more convenient to carry, and will answer as well. A folding easel is easily constructed of three slips of deal, and an india-rubber ring to hold them together at the top when in use; or a straight bolt run loosely through the three at one end, allowing the legs to be stretched out to form a tripod. The sketch block rests on a couple of pegs fitted into holes in the front pair of legs at the required; height, Fig. B; a more complete affair is given in Fig. C, from a catalogue of Rowney's. All these bought contrivances are, However, sold at too high a price, and any ingenious hand at the plane and chisel can make such at one quarter the sum demanded at the shops-in point of fact, a great number of beautiful sketches are taken without seat or easel, a fallen tree or stone, or the dry ground supplying the first, and the knees the second, and it is a nuisance on a hot day having much to carry. into the handle is of use, not only to protect the sketcher from what may be a dangerously hot An umbrella, however, with a spike to screw sun, but to prevent the colours from drying too rapidly. A short three-legged camp-stool can be strapped to an umbrella, and the latter used as a walking-stick without inconvenience, a light easel may also be strapped to it, and in a pocket, made inside for the purpose, pencil, rubber, brushes, &c., can be conveniently stored. On the whole, it is hardly possible to make a better arrangement. Let it be remembered that in a sketch you will not require deep or elaborate heavy handling and dirty tints. Aim specially at colouring. The general fault of the beginner is FIG. C. steam-tight. The tide was strong against the little them to the tubes, and it is no use wasting money clearness, and remember to sacrifice ever to vessel on her run down, yet, on the measured mile in the Lower Hope, she attained a speed of 8.33 in this, which is a matter of choice or habit. I knots, with nearly one and a-half knots of tide think it is, however, advisable to have a small against her. This was not a trial run, and no spe- palette knife for taking up a little colour from the cial precautions were taken to secure a good result; paus. With a rag at hand to wipe the knife but there is no doubt that the result is very good (an instantaneous operation), the mixing of indeed considering the size of the boat. The colours is less likely to occur than if the brush shadow, while such detail is clearly seen under a general particulars of the run may be thus sumn.ed up: The Filga left Blackwall at 12:30, passed North Woolwich Railway Pier at 12:55, and Erith at 147 p.m. Gravesend was reached at 248, (often being wet), is dipped into the cells. An light. The whole beauty of a scene frequently arises from the light which falls upon it, and out interest is thus rendered picturesque and what under other conditions appears wholly withlovely, Recollect in your work that bright light absorbs or conceals detail, and so does deep of your sketch will be neither intense light nor half-light. Observe, also, that the greater part deep shadow, both of which occupy small points only, from which are many gradations of the one into the other. It is generally recommended to succeed after the former has become quite dry, and Voit on the one hand, and by Fick and Wisbegin colouring a sketch systematically by carry- but this should not cover the whole. Upon these, licenus on the other. The former have investiing a broad wash of colour, blue, or red, or when dry, may be laid partially another tint, say gated the amount of nitrogen excreted from a body, orange of a light tint, over the whole, and then of vandyke or madder brown, both of which are both in activity and in rest, the quantity of food the operation is to be repeated, omitting to transparent. If a patch of green is required, lay consumed being the same in either case, The two cover certain parts with this ground tint. The a thin wash of cobalt upon the pure yellow, and last-named experimenters have measured the quanobject is two-fold-to shut out the white paper, you will have it at once, and thus your wall will tity of nitrogen excreted during the violent musand to ensure breadth or uniformity of treatment. be of various hues, but all clean and transparent. cular exertion occasioned by the ascent of the The fault is (and it is often fatal) losing the For the highest light leave the pure paper. This Faulhorn. Now, since the quantity of nitrogen purity of the colours afterwards laid on. An is one way of work, and a safe one. The second, given off from the body can result only from the deadept will, no doubt, improve his work by such nevertheless, is more artistic, and, in some re- composition of the albumen taken up as food, these treatment a novice will spoil it. The white specta, better. Make a wash of ochre, another of experiments lead to two certain conclusions. They paper is most precious-it has to express your burnt sienna, a third of madder brown, a fourth prove, first, that, during the activity of the body, light from first to last; and even those light of sepia. Begin at the top with the ochre, and no more nitrogen is evolved than during rest; and orange, or other tints used over surfaces illumi- carry it irregularly downwards; then dip into secondly, that if, from the amount of nitrogen nated by the sun, depend for effect of light upon the burnt sienna with the same brush, give a quick given off during muscular effort, the quantity of being laid on thinly, thus permitting the paper stir or two, and so mix partially, and proceed albumen is calculated which must have been deto appear partially through the colour. Points to lay it on. After awhile do the same with the composed in order to produce it; this amount is of high light must be left wholly uncovered, and madder and sepia, and carrying this to the end, not sufficient, even if consumed in a furnace, to in all the purity of the white paper itself. Do leave all to dry. You ought to have a beauti-account for the amount of labour performed. The not, therefore, sully your work by broad washes fully-varied tint; perhaps, however, harsh lines greater number of German physiologists are, to constitute an under-tint, and to ensure what is will appear here and there. If so, leave it alone therefore, at present of the opinion that in muscalled "keeping"-i.e., a uniformity of appear- till quite dry, and then wash with a large soft cular activity it is not albuminous substances, ance, but colour each part at once with the tint brush of pure water, and again let dry. You but non-nitrogenous substances, such as the required, laying it on carefully and steadily to may practise all this at home even better than out- hydrocarbons, which are consumed; and, owing the outline. To do this well, needs some practice; of-doors, for you must be eventually able to to the relation of albumen to the latter, the out-of-doors it has to be done rapidly so that the gradate in all sorts of ways firmly and surely; muscular system has been compared to a machine, whole may be laid before any part has dried, or sometimes with colour over colour (the chromo the moving portion of which is formed of albuthe colour will be patchy and uneven. Suppose you have to colour the gable end of a plastered lithographs are done thus), and sometimes by menous substances subjected to a continual procottage on the light side, it will generally be running one wet tint into another, as described. cess of waste and repair. The motor force, on the Try also to gradate from dark to light, and other hand, furnished in the case of the steamslightly yellow, or it may be, perhaps, light-vice versa, in one colour-say sepia, for practice. engine by the fuel and the steam, is, in that of the brown. Make a wash of yellow-ochre, sepia, Rub a full rich dark tint in a saucer, and after body, solely the result of the oxidation of the hydrovandyke brown, or other colour that appears to match the original. Let it be a thin, clear light laying on a little of it, add a drop or two of carbons. lience, during muscular activity no more wash, not pasty, nor dark, or thick. Take a sable water and go on again, then more water, picked albumen is consumed than during rest, but more brush, fully large, and dip in the colour, so as to up from a glass without washing the brush, and hydro-carbons. Voit has gone a step further, and take up plenty, but not enough to drop from the Every time you add the water investigated the reciprocal functions of albumen brush. Your picture being on a slope on the easel, stir up with the brush, and never run the latter and the hydro-carbons in the joint nourishment or on your knees, begin at the peak of the gable, too dry, because you need a line of liquid of the body. He fed dogs on pure flesh freed as lay colour up to the edges at once, down the in- paint at the lower edge of your work as you far as possible from fat, and carefully set down cline of the roof, then draw back a little and proceed, so tint may blend the change of weight in their bodies, and the quancarry the tint down, then to the edges of the with the old. In a similar way vary the tity of nitrogen which was given off during this gralls, and so again rapidly back and downwards, character of the tints. Take up light red, carry time. The result of these experiments was the keeping a full brush, so that the colour may it into Indian red, then into burnt sienna. You remarkable discovery that, even with a diet very flow easily down the paper. If it should run will soon see that your powers increase, and your rich in flesh, the animals scarcely increased in down in streams by itself, shake a little out of work will become easy and delightful. Most of weight, but were only just able to equalise waste your brush, but go on, don't stop (except for a your sketches will depend on broad and varied and repair. The more flesh free from fat was second to dab up the colour, if it has gone much washes of this kind, but you will have to lay in given them, the more completely was it assimitoo far, and is likely to sully any other tint in its detail over these with a drier brush. Don't get lated in the body without its organs becoming way), and when at the bottom of the gabled the sketch generally too dark or heavy, and let richer in albumen. wall, take up on the brush dried for the purpose, it remain as a sketch, don't finish it at home. any extra colour that may lie there in a wet line, Copy it and work a more elaborate drawing if and if you have done well you will have a beanti. you like; but I suspect the sketch after all will ful clear light tint of great purity. Thus, also, prove the best for a long time. But I must map down all your patches of colour, each by cease, though I should like to have written a good itself and to its proper limit, and where bright light falls, stop with your brush rather more dry, so that there may be a clear edge, but not a harsh line, and resume below the point of THE VALUE OF DIFFERENT ARTICLES amount of flesh in the food, the absorptive and high light. These bits of light, or broad light, as the case may be, add greatly to the beauty of very a sketch, so guard them carefully throughout. Now by this mode of work your sketch will probably have a raw appearance, and will be generally pateby, without that uniformity, oneness, or keeping, that is so desirable. Never mind at first, remember you are learning to sketch from Nature, and to lay on colour clear and bright and true to the original, and you have, as you will find, work enough to do, without troubling about those higher qualities in which artists excel. Yet, be it observed, if you can correctly copy the tints before you which express the light and shade and colour of the various objects in their due proportions, you will have breadth and keeping too, and Nature will have already taught you that she manages these details of art rather better than those who are guided by arbitrary and artificial rules. The reason you will not succeed in this at first is because the untrained eye fails to appreciate the colour, tint, shade, &c., of the natural object-does not at first catch those niceties of gradation which become evident to the more educated sight. You will find after a few trials that the same tint does not in Nature extend far over any given surface. Even the cottage wall, if carefully observed, will be found to be of various colours-here a pure yellow, there a pale brown, in another place light red, in another, greenish, from dampness, and so forth, and an accurately-coloured sketch would of course so represent it. At first, however, the learner will certainly fail to be impressed with these minutia of tint. The sketch, nevertheless, will lack variety if too large a surface is coloured uniformly. Hence one of the following methods may be adopted :-If a tint of yellow ochre has, as supposed, been used, a wash of light red may continue. deal more. that the new OF FOOD. J. L. If the amount of flesh given was inconsiderable, a loss of weight took place, the animal giving off more albumen in the form of excreta than it took up with its food. Comparatively small quantities of fat had a remarkable influence on the process of I nourishment. Under this latter treatment the quantity of nitrogen excreted immediately declined, and when there was a somewhat larger excretive process were found to balance each other. If the proportion of flesh in this mixed Tmore than a generation by Baron Liebig, place in the body than could be obtained by an HE theory of nourishment, advocated for diet was increased, a greater increase of flesh took which divides food-substance into nitrogenous and exclusively flesh diet, however generous. These non-nitrogenous, has of late years given occasion facts have led to the conclusion that the hydroto many physiological investigations. The most carbons diminish the decomposition of flesh in recent and most thorough of these we owe to Pro- the body. The addition of fat to the diet can fessor Voit, of Munich, who has followed, by the never entirely replace albumen, but renders various circumstances within the organism, of the close connection with these investigations of food most careful analysis, the transformations, under necessary a smaller portion of it in the food. In substances which are absorbed into it, and those comes the question of the value as nourishment of which are excreted from it. According to Liebig's the extractum carnis (see Academy, No. 5, p. the nitrogenons, fat, starch, and sugar, of the first prepared by Liebig contains nitrogenous classification, albumen is the representative of 132). It is well known that the extractum carnis non-nitrogenous, articles of food; and he assigns substances soluble in water, which, together with to the two kinds different offices in the economy albumen, occur in flesh. As they form an essenof the body. Starting with the view that the tial ingredient of broth, it follows that they play motor muscles consist mainly of albuminous substances, he enunciated the theory that the function It must not, however, be forgotten that a very a definite part among the constituents of food. of albumen is to produce mechanical labour, that important element of broth is wanting in the is, motion. This view is confirmed by the ex- extractum carnis-viz., gluten and fat, which perimental fact that a generous meat diet makes men strong, while the want of flesh-meat renders compose the greater part of the solid portion of them weak and incapable of endurance. Horses carnis is of very great service in nourishment it broth. Although, therefore, the extractum which have to perform great muscular efforts, is going too far to believe that it can ever be a must be fed on oats, which are much richer in substitute for broth. Liebig has conjectured that albumen than the ordinary articles of vegetable diet. It is further confirmed by the result of all and hydro-carbons, forms, together with the a vegetable article of food containing albumen experiments, which show that life cannot be sup- extractum carnis, a complete diet, and that ported on fat, starch, and sugar, without albumen. All animals fed in this manner die of debility. To this combination has the same effect as 22 the non-nitrogenous articles of food, Liebig theremeat meal. In order to verify this conjecfore attributed another purpose, and held that ture, Bischoff has fed dogs upon bread, and has they are employed in the chemical process of observed the result of the addition of extractum, respiration. In connection with this inquiry, the carnis. The conclusion arrived at was, however next question was, whether more albumen is con- that the latter had very little influence. Whether sumed by the body when in a state of muscular it be added or not, animals fed on bread decreas activity than in a state of rest. This problem has in weight, and on this diet cannot be made to live been approached in two different ways; by Bischoff very long. |