frames, solid at the sides and well-glazed, and inform him that he has at his disposal any amount of rotted leaves and stable manure. He will tell you that he can do nothing with them. They are cucumber frames in his eyes, and nothing more. Yet no better appliances, nine times out of ten, are at the command of the gardeners who decorate the beautiful villas that surround Paris with floral beauty from May till November, as they can testify who saw them deserted, but in all their beauty, when the Germans invested the great capital. If an Englishman wishes to attain the same results by the same small means, he must either become his own gardener, or he must break his' gardener's will to his own. Given such a frame as we have spoken of, and four or five hundred of the hardier geraniums-such as Tom Thumb, Tom Thumb's Master, Lady Constance Grosvenor, and the Duchess of Sutherland -may with care be carried through the coldest and, even what is far more trying, the wettest winter. What are termed the foliaged pelargoniums, such as Mrs. Pollock, Bijou, and Star of Spring, will not, it is true, or but rarely, endure this simple treatment; but if the bright and flowering geraniums are preserved, the exquisite charm and variety that are given by foliaged plants can be still more easily obtained by other Abundance of white is a sine-quá-non in the bedding-out style of gardening; and white may be secured to an unlimited extent without the aid of so much as a pane of glass. Cerastium Tomentosum, with its beautiful silver-gray leaves, is as hardy as common grass, and can be propagated by division either in the late autumn or the early spring. It is to be seen in almost every cottage garden, only there it is allowed to flower, as it must not be when intended to serve the purpose of which we are speaking. Another most useful and lovely white plant is the Cineraria Maritima, which has only to be sown under a south wall, from seed, in September, to be left out all the winter, and to be potted in spring, to make a famous show by the end of May. After white in importance comes blue; and the best, indeed the only good blue, unfortunately, the Lobelia, can be grown by any one who can make a hotbed of stable-manure in February. By its side, in the same manner, may be raised the Oxalis, that lovely bronze-coloured clover; the tall Perilla; and last, but anything but least, the Pyrethrum, or Golden Feather. Only, in all these instances, care has to supply the place of extravagant outlay; whereas extravagant outlay is just the one thing that delights the English gardener most." means. Now, as a matter of fact, a greenhouse will cost no more to construct than the requisite frames to preserve and propagate an equal number of plants; while it is immeasurably more convenient for the gardener, requiring less labour and time for the due performance of the various attentions necessary for the health and welfare of his patients. Besides, frames with their fermenting masses of leaves and stable manure can be made to yield a more profitable return from early vegetables than "bedding-out" stuff would give-doing this, moreover, while the latter is in "winter quarters," and then coming in handy for the "hardening-off" process. EL ELECTRICITY: WHAT IS IT?—II. This similarity in nature between heat and We know that no other forces, save heat and electricity, can effect the decomposition of any compound by apparently destroying the affinities of its elements for each other; we likewise know that electricity will decompose substances that defy any other means of analysis; and that electricity is convertible into the most intense artificial heat and light known. Can we fail to see the significance of this fact, which distinctly points to their similarity of nature? Even the simple evidence of their being convertible into each other is sufficient to show that they have a common origin, and beyond this we find they act in the same way, and have a connection so close that it is impossible to produce the one without the other. Heat destroys the affinities between the constituents of compound bodies, or at least suspends them, by removing the atoms beyond the sphere of each other's attraction; and taking any example we may, the heat required to decompose a compound body is exactly the same in amount that was given off in its composition. For example, take the gases, oxygen, (O) and bydrogen (H); like all gases, they contain a large amount of latent heat. When they combine to form water OH,, the greater part of this is given off, because the latent heat of water, and indeed all liquids and solids, is considerably lower than that of a gaseous body; but it will be seen at once that to again pass into the gaseous state, the oxygen (0) and hydrogen (Hg) must be supplied with the same amount of heat that they gave up when forming water, and with less than this amount they will not be decomposed, except when electricity is employed; that the electricity has given them a different force to that which they possessed before cannot be admitted, for they will yield just the same heat on again forming water as in the first case. So much for the expense of the system. There is another side to the question as to the advantage of the present arrangement of flowering and brilliant foliaged plants. The gorgeous masses of colour are, no doubt, pleasing when set out in a harmonious manner, but they require to be surrounded with large masses of green, as much to exhibit their full beauty as to relieve the eye, which is apt to be dazzled by the glaring lines of yellow and scarlet -the heat, in fact, of the "painted carpet" produced by "solid planting." For this reason the "solid" style is utterly unsuited to small gardens where grass is conspicuous by its absence; and the plants should therefore be so placed that they may develop their foliage and permit the Again, if a current of electricity which proearth to be seen between them. Independently duces the greatest heat and light known to us can of all this, the aspect of the subject which we are also decompose substances which no other agent most inclined to look at is left out in the cold- will touch, and that this decomposition can only the individuality of the plants is utterly destroyed, be effected by an amount of heat being supplied and the mental pleasure which might be derived to the molecules sufficient for their constituents from a study of their physiology and life-history to exist in an uncombined state-so far as we are is lost in the mere sensual gratification of harmoniously arranged colours. The principal value of a garden to our readers consists in the facility which it affords for the study of vegetable physiology and the refining influence which a contemplation of the works of Nature must always exercise upon the mind. How this may best be carried on, with the further advantage of having flowers all the year round, we shall probably explain at some future time. able to discover-would it not be a remarkable I believe I am right in stating that when the 200° C. is given out in the combination of oxygen and hydrogen, and forms water, and therefore that a motion corresponding to this heat must be supplied by the electric current when it effects the decomposition of water, and this supposition is perfectly consistent with fact, for a very powerful current is required to decompose water alone; and the heat developed in a bad conductor, such as water is, increases enormously with the augmentation of battery power. Here, then, I think, we can approach nearer to the theory I am trying to explain than we have hitherto done; for, besides having the conditions necessary to produce the required heat for the decomposition of OH, (water)-a powerful current and poor conductor, itself a proof almost of the agency by which the water is decomposed-we can (retaining the same arrangement of decomposing cell) apply heat direct, instead of the electric current, with exactly the same result. Thus, if the platinum electrodes of the voltameter or decomposing cell be beated by the oxy-hydrogen flame, the water is decomposed the same as with a battery; showing, again, how intimately connected the two modes of motion, of heat and electricity, are. The influence of pressure in the decomposing cell also tends to confirm this theory, for, if an electrolyte in a decomposing cell be submitted to pressure, the decomposition is entirely suspended. The expansion consequent upon increased temperature and ultimate decomposition prevented, the current manifests itself as heat, instead of being rendered latent; observing exactly analogous laws to those of heat in relation to constant pressure and constant volume. being Following the above course of reasoning, I think we shall be able to comprehend more clearly what occurs in a decomposing cell or ordinary voltaic battery. The first effect of the voltaic current is to polarise the molecules of the electrolyte, which, I think we have proved, is accompanied by a motion of them; this motion represents, or is virtually, a certain amount of heat; indeed, a great part is manifest to us as heat; and if the rapidity of vibration is sufficient, the heat is supplied requisite for the constituents of the compound to exist separately; of course, this amount varies with the compound being decomposed. In the case of water, as we have before shown, the heat required is very great. When, however, a small quantity of sulphuric acid (SO,HO) is added, the water is decomposed readily by two or three batteries, on account of a secondary action. O being liberated at one pole and H, at the other, the SO, (sulphuric anhydride) combines with another molecule of H2O (water) to form again SO2HO, or H2SO4, and so the action is continued. I have taken all along water as the example. to work with, but any other compound will answer just as well, and the same reasoning apply to it; for instance, take CuSO, (sulphate of copper), where we have a compound in which the base Cn (copper) gives out very little heat in combining with H2SO, (sulphuric acid); indeed, it does not combine very powerfully at all, but is easily displaced by other metals; in this example of weak affinity we might reasonably suppose that a weak current would effect their decomposition; such is the case, CuSO, is even decomposed by one cell of a battery. Going a step further to the voltaic cell itself. I think it is very generally admitted now by scientific men, that "chemical affinity" is identical with "electrical attraction;" indeed, modern chemistry divides the elements into chlorous and basylons, or + and; and it will be admitted that all bodies vary in their susceptibility to electrical action; or, if we may use the term, in their affinity for it. Friction is the readiest method of developing it, and when developed in this way is called statical electricity. The theory to account for this which finds most general acceptance is, that the development of electricity is the result of the separation and renewal of contact between dissimilar bodies, and electricity is distributed amongst thera in quantities proportional to their affinity for it (or may we not say to their power in rendering it latent ?). Now, let the affinity of glass for it be represented by 4, and the affinity of a rubber of silk by 6, making together 10. When these bodies are brought together, this relative finity may be supposed to be charged, the electricity being nearly equally distributed over the two bodies: the affinity of the glass, then, in this case, would be increased from 4 to 5, the affinity, of the rubber decreased from 6 to 5, the total, 10, remaining the same; when we separate the rubber from the glass, or break the contact, the origins! affinities, 4 and 6, are restored, whilst the new distribution, 5 and 5, remains; the quantity of electricity in the glass, therefore, has been increased by 1, and hence is positively electrified and the rubber negatively. The same kind of reasoning must be employed to explain the effect of contact between the dissimilar metals in a voltaic battery. It was this behaviour, probably, that led so many of the earlier electricians to believe that contact alone was necessary to generate a current of electricity. Now, taking one of the simplest voltaic batteries-a plate of amalgamated zinc and a plate of copper immersed in dilute sulphuric acid-s0 long as the plates remain unconnected no current circulates, nor does any decomposition occur, at least, very small in amount, if any, due to the ordinary affinities of the plates for the elements of the compound; but when the two metals, zinc and copper, are connected by a conductor, powerful chemical action ensues, accompanied by a current of electricity, which, indeed, it has generated. The strength of the current, too, is always proportional to the amount of zinc dissolved in a given time, and it is one of the important points which should be noticed, as will be seen afterwards. The amalgamated zinc has little power of itself to separate the constituents of the liquid in which it is immersed, but on receiving additional assistance from its connection with the copper by the new distribution it has its affinity or electrical attraction increased sufficiently to overcome the existing affinities between the elements of the solution in which it is placed, and thereby decompose it. But we have said that the same amount of heat or motion is required to decompose a compound that was given off in its composition; applying this to the point in question, I should say that the affinity of the zinc now represents an amount of heat or force equal to that required by the elements of the electrolyte to exist in a separate state-i.e., the H, has an amount of heat given to it, must have, to enable it to take the gaseous state as it does; and so must the O, or the O and H, would not part company. Indeed, any body in passing from the solid or liquid state to the gaseous absorbs large quantities of heat. From whence does this heat come? We are obliged to refer it to the new affinity obtained by the contact of the two in its effects this heat. The oxygen, however, liberated in the battery we have been speaking about, does not continue in the gaseous state, as the H, liberated at the copper plate does, but combines with the zinc, forming oxide of zinc (ZnO), and in doing so, of course, gives up again, more or less, the force which it absorbed when parting with the hydrogen. What is this force? Where does it go? I think we cannot fail to see that it is this force which, when supplied with suitable conditions to circulate through a conductor, is called the electric current, though, of course, it must have undergone some modification from the true form of heat. If the suitable arrangement is not supplied, no sign of electricity is present, but the chemical action manifests itself as heat. It must be remembered that part of the current must return to the zinc to again render it electro-positive, otherwise all action ceases. amount of force or heat is lost proportional to the work done; but if the machine is not working, the force or heat is found to be distributed over all the parts of it. (To be concluded in another paper.) SMELL. : THE Moniteur Scientifique contains a paper by M. Papillon on this subject, having reference to recent discoveries in chemistry and physiology. We extract from it the following:The seat of the sense of smell is, as we know, in the lining membrane of the nostrils. This membrane has a mucous and irregular surface, over which spread a number of nerves, with delicate terminations. It secretes a lubricating liquid. By means of muscles, the apparatus of smell is dilated or contracted, like that of sight. The mechanics of smell are, simply, the contact of odorons particles and the olfactory nerve. These particles are carried by the air into the nostrils. If, on the one hand, the nerve is injured, or even compressed; if, on the other, the air is prevented from passing into the nostrils, there is an absence of smell. The upper part of the nostrils is the most sensitive as regards odour. The sense of smell varies much in different people. Some are entirely without it. Others are quite insensible to certain odours: a case similar to that of Daltonism, in which some eyes fail to perceive certain colours. It is recorded of a certain priest that he perceived no odours but those of smoke and decayed cabbage, and to another person vanilla seemed quite inodorous. Blumenbach speaks of an Englishman who could not perceive the fragrance of mignonette. Smell is sometimes voluntary, sometimes involuntary. In the former case, to obtain a lively sensation, we close the mouth, and make a long inspiration, or a series of short and jerking ones. The muscles contract the orifice of the nostrils, and thus increase the intensity of the current of air. On the other hand, when we wish not to smell, we expire through the nose, so as to drive away the odorous air, and inspire by the opened mouth. Smell and odours are closely connected with the phenomena of taste or gustation. Most savours perceived by us arise from a combination of sensations of smell with those of taste. There are, indeed, only four primitive and radical kinds of taste-acid, sweet, salt, and bitter. This may be shown by experiment. If we close our nostrils will come under one or other of these four heads. on tasting any sapid substance, the perceived taste Thus, when the olfactory membrane is diseased, the savour of food is altered. How do odorous substances act with reference to the matter which separates them from the organ of smell? Prevost, in 1799, showed that if an odorous body were put in a saucer full of water, the emanations from it agitated the molecules of the water visibly. These motions, of which camphor gives a very good example, have been recently studied by M. Liegeois. He found that some substances caused movements of gyration and translation over the water surface, similar to those of camphor. Of this class are benzoic acid, succinic acid, and orange bark. In the case of others, this motion ceases very soon, as they become encased in an oily layer over their surface. He thinks these motions are due, not to a disengagement of gas, causing something like recoil, but to the separation and rapid diffusion of the odorous particles in the water. The fluid shows affinity for these. Similarly, a drop of oil falling on water sends out an infinite number of very small globules, which spread through the liquid, while the volume of the drop is not sensibly diminished. So with aromatic essences. Though insoluble in water, the small odorous particles tend to disperse themselves in it. A small quantity of odorous powder will thus impart perfume to a large body of water. This theory, if I may call it such, I think we shall find applicable to all the phenomena observed in a battery, for the strength of a current produced by a given expenditure of zinc is always proportional to the amount of work it does in overcoming the resistance of its conductors, and if the current loses strength by the interIt is these same odorous molecules which are position of work its equivalent is always found carried to our nostrils. And the action of water in the work done, whatever that may be, is thought by M. Liegeois to assist in the formawhether to induce magnetism in iron, work tion of them. In the morning, when the ground machinery, or circulate through a long conducting is moist, and the flowers are covered with wire; just as there is with heat, so is there with electricity a true mechanical value. Another important thing for us to notice here is, that if there is not sufficient work for the battery to do, the surplus force turns directly into heat, the behaviour being exactly analogous to that observed in machines where heat is the motive power. If the machine is made to work, an dew-drops, there is a large exhalation of perfume. Similarly, after a shower of rain. In gustation we have something analogous: the saliva is fitted to diffuse the odorant principle; by the motion of the tongue in the cavity of the mouth, this diffusion is promoted, for the surface of evaporation is enlarged. Now, in the same way as the small particles diffuse themselves in water do they diffuse themselves in air, which then becomes the vehicle carrying them to our nostrils. Some odorous substances have a very great diffusibility. Ambergris, newly cast on the shore, is smelt a long way off. Bertholin states that the odour of rosemary off the Spanish coast is perceptible long before the land comes in sight. The degree of division of the particles is in some cases marvellous. A grain of musk will perfume an apartment for a whole year, without sensibly losing weight. Haller mentions having kept for forty years some pieces of paper perfumed with a grain of ambergris, and at the end of that time they still retained their odour. It is to be noted that the odorous particles are sent out, and the body emitting them does not act as a centre of agitation, giving rise to vibrations. It is thus a different case from those of light and heat. The odour is the odorous molecule itself; whereas light, as perceived, is not the luminous body. We cannot tell whether oxygen has some chemical influence on the particles; nor what kind of action takes place on contact of the particle with the nerve, whether a mechanical agitation or a chemical decomposition. But the distinction of the senses into physical (sight, touch, and hearing) and chemical (taste and smell) is a just one. In the latter, contact is always implied. Thus An able writer has recently tried to prove a kind of music in odours. That is, different odours, according to him, affect the olfactory nerve in various degrees, corresponding to those in which sound affects the auditory nerve. we may have octaves of odours. He enumerates various substances that produce the same impression, but in different degrees; e.g., these four, almond, heliotrope, vanilla, and clematis. combination he obtains semi-odours, correa rose with a sponding to semitones; e.g., geranium. He points ont principles of harmony in perfumes corresponding to those in colours, and thinks it possible to produce a desired perfume from a mixture of others. By The theory is ingenious and worthy of attention, but it is open to grave objections. For the harmony in colours and sounds depends on exact numerical relations, which may be accurately determined; whereas, in the case of smell, the criterion is capricious and uncertain, and it is not possible to reduce to formula what our sense reveals. There are many cases of hallucination as regards smell; united, generally, with insanity on constantly complained of a fetid odour; others other points. Lunatics have been met with who rejoiced in the most delicious, though imaginary, perfumes. M. Lelut tells of a patient in the Salpetrière, who was continually troubled with the smell of dead bodies, which she thought to have been buried in the establishment. Capellini mentions the case of a lady who could not bear the smell of a rose, and fainted one day when a friend came in with one that was artificial in her hand. Many other instances could be given. It seems to be well authenticated, that in lunatic asylums these delusions as to smell are very frequent. The intensity and delicacy of the sense of smell vary in different individuals and races. In some it is wonderfully sensitive. Woodwart tells of a woman who predicted storms several hours in advance, from the sulphurous odour (due to ozone probably) which she perceived in the air. A young American who was deaf, dumb, and blind, became a good botanist, simply by the sense of smell. It is, however, in some of the lower animals that we find the sense most highly developed: ruminants, pachydermous animals, and, above all, carnivorous mammifers. Smell is, with some of them, like an eye, which sees objects, not only where they are, but where they have been. The keen scent of the dog is well known. Humboldt mentions that when, in his travels in South America, it was desired to attract condors, all they had to do was to slaughter an ox or a horse, and in a short time the odour attracted a number of these birds, though none were visible previously. Of birds, waders have the largest olfactory nerves, and their sense of smell is most highly developed. The olfactory organ in reptiles is large. Fishes also have an olfactory membrane; and fishermen have observed that they are driven away when certain odorons substances are thrown into the water. Sharks and other voracious fishes often gather from great distances when a carcase is thrown into the sea. Crustaceans are not insen of every brake on the train may be almost simultaneous with the intimation of danger, depending solely on the quickness or smartness with which the driver puts in operation the means at his disposal. Under the present arrangement the time occupied in whistling and getting the brakes on often means just the difference between a collision and its avoidance, for although the time thus occupied may seem almost inappreciable, it is frequently of sufficiently lengthy duration to be a trifle too long. It is time, however, that we proceeded to describe what experience has shown to be the best arrangement for stopping trains yet put into practice. The most important part of the the air and storing it up for use when required. Westinghouse system is the method of compressing This is accomplished by an ingeniously contrived engine and pump secured to the outside of the trailer; in fact, on one side of the fire-box in a locomotive, between the driving-wheel and the similar position to that frequently occupied by the Giffard's injector. The piston of the little cylinder and that of the pump are connected together by a rod of a somewhat peculiar section, obtained by cutting or filing down the ordinary circular rod on four sides. The object of this is to to the peculiar arrangement of the steam-valve, prevent the turning of the pistons, which, owing and the absence of guides, &c., would otherwise be free to rotate. The arrangements for the admission and regulation of the steam to the pump engine are of a very ingenious character, and we suffice it to say, that the steam-valve is contained shall probably illustrate them at a future time; in a cylindrical chamber, and is made to rotate to admit and exhaust the steam. This rotatory movement is obtained from a very small piston actuated by steam, situated on the top of the cylinder and working at right angles to its axis. The main piston-rod is hollow for more than half its length, so as to permit the insertion of a rod connected with a valve which admits steam to the small piston employed to rotate the valve-rod. Thus the motion of the piston-rod actuates this valve-rod, and the steam being caused to act upon the same piston, the valve is rotated to the required positions. The air-pump is double-acting, takes its air through a strainer, and also draws in a supply of the lubricator at each strokemineral oils being used for the purpose, owing to the great heat developed by the forcible compression carbonising all other lubricating materials. The compressed air is forced from the pump to a strong cylindrical receptacle carried under the foot-plate of the engine, and it is found in practice that the pump is self-governing, working when the air chamber is full at just sufficient speed to supply the small leakage which unavoidably takes place, but when the pressure which thus opposes its movements is reduced on applying the concentrated force to the brakes, it immediately springinto rapid action and restores the normal press sure. The small engine and pump is capable of a figures thus obtained, but there is another point speed of 100 double strokes per minute in the of view which appears to have been overlooked event of any extraordinary leakage, less than oneby the chroniclers of the experiments. Under third of that speed being found amply sufficient, the present system, as our readers are aware, the however, under ordinary circumstance. driver or the stoker has the immediate control only reservoir is provided with a small safety-valve, so of the brake attached to the tender. In order that whatever the pressure of the steam in the that the other brakes on the train may be applied boiler of the locomotive may be, the pump may be he is obliged to whistle to call the attention of, allowed to work as fast as it can against the presand signal to, the guards, who, it is to be hoped, sure of the air in the reservoir, generally from always pay prompt attention to the commands of 60lb. to 70lb. per sq. in. The compressed air is the driver thus conveyed. As many of our led by a pipe from the reservoir to a three-way readers will not require to be told, however, long cock placed conveniently to the hand of the driver, acquaintance with danger renders those callous which communicates by one pipe with a three-way who have to face it; and although we are inclined cock situated beneath the foot-plate, and by the to be reticent in insinuating that guards do not other pipe with the atmosphere. In connection always pay that attention to the whistle of the with this second three-way cock are inch iron gasdriver they are supposed to do, there cannot be pipes, fixed beneath each carriage one on each the slightest doubt that far too much is left to side, the joints between the carriages being made their care; in other words, that the command of with stout specially prepared indiarubber tubing the train is taken out of the hands of the man best and an ingenious coupling, the air-tight fit of capable of governing it, to an extent which should not which is secured by means of the compressed air be allowed when a remedy is pointed out. But itself. The object of having two sets of pipes is granting that the guards are always on the qui partly to insure against mishap to one set of tubes, vive, with their hands on the brake wheel, ready in which case the other would be sufficient for all the at the first intimation of danger to apply the purposes required, and partly to facilitate means of stopping the train under their control, the connection of the different carriages; for it must be acknowledged that with trains travelling the couplings, being provided with male and female at 50 miles per hour even fractions of a second are screws respectively, and all the carriages being valuable amounts of time, and it is only too true, fitted alike, it is obvious whichever end of the having been proved in numerous instances, that carriage it is desired to couple will present the the waste of these fractions of time in whistling pipes in the required position, which could not be and in getting the brakes put down, has often the case if only one pipe was employed. The resulted in accident, or rather has failed to pre-coupling is fitted with two valves, which, when the vent what would have been, under a better ar- connection is perfect, are both open and allow of ranged system, preventible. With the Westing- the passage of the compressed air, but in the house air-brake, on the contrary, the application event of rupture of any of the couplings by COLOURED SUNS.* F a brilliant star be observed when near the aecilent, or if the connection through carelessness air and nitrogen mixed with the chlorine gener- caused to react simultaneously, carbonate of lime has not been made, the valves close the end of ated partly prevents the condensation of this and chloride of magnesium being produced. This the pipe and prevent the escape of the air. Besides chlorine or its combination with the alkalies and distilled chloride of magnesium regenerates the this self-acting arrangement the driver can, by alkaline-earthy bodies intended to produce hypo- hydrochloric acid, which is again employed means of the three-way cock beneath the foot- chlorites suitable for practical use in bleaching. for the production of a fresh quantity of chlorine. plate, shut off the compressed air from either or The object of M. Tessió du Motay's process is The magnesia remaining serves again for another both of the pipes. while wholly or partially utilising the hydrochloric operation. Thus the reactions which constitute The air being thus led throughout the whole acid employed, to generate pure chlorine in an the process are shortly as follows:-1, the length of the train is conveyed by branch pipes isolated state which can combine without waste oxides of manganese serving for the production to an air cylinder under each carriage. This with the alkaline or alkalino-terrous bodies in the of chlorine are ceaselessly regenerated; 2, cylinder contains a piston packed by a cup-leather, form of bleaching chlorides; and to accomplish the hydrochloric acid is utilised completely for and connected with a rod, to the outer end of this the inventor has discovered two methods. the production of chlorine; 3, all the chlorine which is attached a conical cup, which receives 1. Into a retort heated to a deep red, con- generated is in a pure state, and consequently the thrust rods employed to actuate the brake- taining peroxide of manganese or a mixture of suitable for the production of dry hypochlorites. shaft. A small pipe is inserted in the frout cover peroxide of manganese and lime, a current of 2. The second method only differs from the one of the cylinder to permit the escape of air when hydrochloric acid is caused to pass; chlorine and just described in the substitution of magnesia for the piston is going forward, and to admit it steam are produced and disengaged, and there lime, the chlorides of magnesium produced being when the piston is going back. Thus the whole remain in the retort non-decomposed peroxide of without transformation, and capable of re-engenoperation is readily understood. The driver by manganese and chloride of manganese, or a mix-dering hydrochloric acid by simple distillation. means of the three-way cock placed near his ture of peroxide of manganese, chloride of manright hand admits the compressed air to the pipes ganese, and chloride of calcium. The chlorine is and the cylinders, where it moves the pistons, and collected in the water or led away into a chamber by means of the thrust-rods and gear forces the for the production of dry hypochlorites. Over brake-blocks against the wheels with a degree of the mixture remaining in the retort a current of pressure entirely under the control of the driver, air or oxygen of the same temperature is caused to who can thus by a mere turn of the wrist lock pass, which, in the presence of peroxide of manevery wheel in the train, or bring just sufficient ganese decomposes at once the chloride of friction into play to check the speed and retard a manganese alone or the chlorides of manganese train when running down an incline or through and calcium regenerated from the sesquioxide of a station where numerous points and dangerous manganese alone into sesquioxide of manganese crossings render 50 miles an hour a hazardous mixed with lime, and sets at liberty the chlorine speed. By another turn of the wrist the compressed contained in the chlorides. This chlorine mixed air which bas done its work is permitted to with air and azote or oxygen is led into vats conescape into the atmosphere, and spiral springs taining a mixture of lime and protoxide of manimmediately draw away the brake-blocks and ganese which has been previously produced by the pash back the pistons in the air cylinders. The decomposition of chloride of manganese by an existing brake-gear can be made available for the excess of lime, the soluble chloride of calcium application of compressed air, but where new produced in this reaction having been previonsly gear has to be provided Mr. Westinghouse prefers run off. In presence of the oxygen of the air and to adopt an arrangement of swing brake which of the chlorine it produces immediately sesquipossesses the valuable properties of equalising oxide of manganese and hypochlorite of lime, the pressure on the blocks, however nnequally which in reacting upon the sesquioxide produces they may be worn, and of preventing all jar and finally the hydrate of peroxide of manganese and vibration, none being perceptible, it is said, in chloride of calcium. The excess of lime rematathe first-class carriage to which it has been ing having no longer to set upon the sesquioxide applied on the Caledonian Railway. remains in the state of hypochlorite of lime. Upon this mixture composed of hydrate of peroxide of manganese, chloride of calcium, and hypochlorite of lime, liquid hydrochloric acid is made to react in the ordinary manner. Chlorine is at once disengaged by the reaction of this acid on the one hand upon the hydrate of peroxide of manganese and on the other upon the hypo chlorite of lime. This chlorine is led into the chamber for the production of hypochlorites. After this reaction it remains in the vats of the chlorides of manganese and calcium. Upon the chlorides of manganese and calcium an excess of lime is again caused to act, which reproduces the mixture of protoxide of manganese, chloride of calcium, and lime already referred to. The soluble chloride of calcium is then run off, and there remains in the insoluble state a mixture of protoxide of manganese and lime, which will serve for other similar operations by repassing under the action of chlorine and air to the state of hydrate of peroxide of manganese, chloride of calcium, and hypochlorite of liquid lime. Mr. Westinghouse has also devised a simple system of signalling between passengers, guards, and driver, which depends on the adoption of the atmospheric brake, however. It consists in fitting each carriage with a small reservoir, which is supplied with compressed air every time the brakes are applied. Wires lead from the different compartments to a lever in connection with a valve in this reservoir, which lever also works a kind of semaphore indicating the part of the carriage whence the signal was made. The valve being opened, the air rushes along the pipes and sounds whistles near the driver and in the guards' vans. These whistles are also unavoidably blown when the brakes are put on, and to prevent the continuance of the sound longer than is required, a peculiar form of whistle is adopted, consisting of a cylindrical pipe containing a loosely-fitting piston, which permits sufficient air to pass to sound the alarm, but which is driven up so as to close the outlet as the volume of air increases. All the details of the mechanism seem to have been well and carefully thought out, as regards both the brake and the signalling apparatus, each of which answers its purpose in an admirable manner. When we further consider that the cost of application cannot amount to a very great sum, that the coupling of the pipes occupies but a few seconds, and that the power of the driver over his train is considerably increased (which means, as we take it, increased safety for the passengers), we are curious to see what action will be taken by railway companies, who have some regard for the money they pay away in damages if they have no respect for the lives of the public. It therefore follows, first, that by the reaction of gaseous hydrochloric acid upon air and oxygen in retorts heated to redness containing peroxide of manganese or a mixture of peroxide of manganese and lime, a first quantity of pure chlorine is produced, which is led away into condensing chambers, and for the production of dry hypochlorites; secondly, that by the decomposition by means of air or oxygen of the chloride of manganese alone, or the chlorides of manganese and lime contained in the said retorts, gaseous com. pounds are produced containing at once oxygen and chlorine. These compounds in their passage across the vats containing the protoxide of manganese and liquid hypochlorites of lime produce pare THE PRODUCTION OF CHLORINE AND chlorine by the action of liquid hydrochloric acid, HYPOCHLORITES. the chlorine in its turn being led into the chambers for the production of dry hypochlorites. Instead NY improvements in the manufacture of of the mixture of protoxide of manganese and chlorine must be, as the majority of our lime in excess, over which the chlorine mixed with readers are perfectly well aware, of considerable air and oxygen is caused to pass just as it comes importance to sundry industries of the United from the retorts, a milk of lime may be employed, Kingdom. We gave an account of an improved which is transformed into hypochlorite of lime. process on p. 55 of Vol. XII., and we are now This hypochlorite as well as the mixture of enabled to give the details of the method recently hydrate of peroxide of manganese and bypopatented by M. Tessié du Motay. According to chlorite of lime treated by liquid hydrochloric that distinguished chemist, the processes hitherto acid regenerates pure chlorine suitable to be taken employed to produce chlorine continuously by to the chambers for the production of dry bypomeans of oxygen or of air and hydrochloric acid chlorites. in the presence of certain metallic peroxides or The chloride of calcium remaining from the dehydrating salts have never given practically operation is collected in vessels wherein carbonate luable results, because the excess of oxygen or of magnesia, or magnesia and carbonic acid,, el tiful phenomenon of coloured scintillation." The colours thus exhibited exceed in purity even those seen in the solar spectrum or in the rainbow. By comparison with them the light which flashes from the ruby, the emerald, the sapphire, or the topaz, appears dull and almost earthy. There are four or five stars which present this phenomenon with charming distinctness. The brilliant Vega in the constellation Lyra, which rarely sets in our latitude, with the approach of spring, this splendid steel-blue is one of these. At midnight in winter, and earlier star may be seen as it skirts the southern horizon, scintillating with red, and blue, and emerald light. Arcturus twinkles yet more brilliantly low down towards the north-east in our spring evenings. Capella is another notable scintillator, seen low down towards the north during the summer sights. But these, though they are the most brilliant northern stars, yet shine with a splendour far inferior to that of Sirius, the famous dog-star. No one can mistake this noble orb as it rises above the southern horizon in our winter months. The vivid colours exhibited by Sirius as it scintillates have afforded a favourite image to the pouts. Homer compares the celestial light which gleamed from the shield and helmet of Diomed to the rays of "Sirius, the star of autumn," which shines with a peculiar brilliancy when laved by ocean's waves;" and, to pass at once from the father of poetry to our greatest modern poet, we find in Tennyson's "Princess" the same image, where he says of Arac and his brothers, that As the fiery Siring alters hae, And bickers into red and emerald, shone Their morions, washed with morning, as they came. It is difficult to persuade oneself that these everchanging tints do not really belong to the stars. But there is now no doubt that they are caused by our own atmosphere. Unequally warm, unequally dense, and unequally moist in ita various strata. the air transmits irregularly those coloured rays Now one colour prevails over the rest, and now which together produce the light of a star. another, so that the star appears to change colour. But it is only low down towards the horizon that these changes take place to their full extent. In the tropics, where the air is more uniform in texture, so to speak, the stars do not scintillate unless they are quite close to the horizon, "a circumstance," says Humboldt, "which gives a peculiarly calm and serene character to the celestial depths in those countries." caused by peculiarities in the quality of the light But the stars are not wanting in real colours, which they emit towards us. In tropical countries the colours of the stars form a very obvious and a very beautiful phenomenoa. The whole heaven seems set with variously coloured gems. In our latitudes, none but the brightest stars exhibit distinctly marked colours to the naked eye. Sirius, Regulus, and Spica are white stars; Betelgens, Aldebaran, Arcturus, and Antares are red; Procyon, Capella, and the Fole-star are yellow; Castor exhibits a slightly green tint; while Vega and Altair are bluish. Antares, which we have described as a red star, presents, when carefully watched, a greenish scintillation so peculiar as to have early attracted the notice of astronomers. The green tint of Castor had been found to arise from the fact that the star is double, and one of the components green. But, for a long while, powerful instruments failed to exhibit a companion to Antares. At length General Mitchell, with the great refractor of the Cincinnati this brilliant red star-the Sirius of red stars, as it Observatory, detected a minute green companion to has been termed. But, as we have said, the stars which present distinctly marked colours to the naked eye in our latitudes are few and far between. It is in the telescope that our observers have to seek for a full From Essays on Astronomy," reviewed on p. 291. "Coloured Suus" appeared originally in The esser on view of the delicate phenomenon of coloured stars. When a survey is made of the heavens with a powerful telescope, peculiarities well worthy of careful attention are revealed to the observer. We have seen that there are no stars visible to the naked eye which are decidedly blue or green. The ancients, also, recognised only red and white stars. In the telescope, this peculiarity is still observable when single stars only are looked at. We meet with some telescopic stars, the depth of whose red colour is remarkable. There are stars of a fiery red, of a deep blood-red, and of a full orange colour. There is a well-known star entitled the "garnet star." And, in fact, every variety of colour, from white through yellow and orange to a deep, almost dusky red, is met with among the single fixed stars. But there is no instance throughout the whole heavens of a single green, blue, or violet star. The case is altered when we come to examine those double, triple, and multiple stars, the observation of which is one of the most pleasing employments of the amateur telescopist. Amongst these systems we meet with all the tints of the rainbow, and with many colours which are not seen in the rainbow, such as fawn-colour, lilac, gray, and so on. The attentive observation of the double stars," writes the celebrated Struve (who detected 3,000 of these objects) "teaches us that, besides those that are white, all the colours of the spectrum are to be met with." "Here we have a green star with a deep blood-red companion, there an orange primary accompanied by a purple or indigo-blue satellite. White is found mixed with light or dark red, purple, ruby, or vermilion." Sometimes a single system offers at one view many different colours. Such is the case with the remarkable group detected by Sir John Herschel within the Southern Cross. It is composed of no less than 110 stars, which, seen in a telescope of sufficient size, appear, Herschel tells us, like "a casket of variously coloured precious stones." It will be well to examine some of the collocations of colour, that we may trace the presence of a law of distribution, if such exist. We have said that blue stars are not met with singly in the heavens. Among double stars they are common enough. But they are generally small. When the larger star or primary is not white, it is usually either red or yellow; then the smaller star or satellite, as we may term it-is frequently blue or green. But this is so far from being a law without exception that the more common case is to find both stars similarly tinted. Amongst 596 bright "doubles," Struve found 375 whose components were similarly coloured, 101 whose components presented colours belonging to the same end of the spectrum, and only 120 in which the colours were totally different. Amongst double stars whose components are similarly tinted, by far the greater number are white, yellow, or red. But there are some instances of double blue stars; and in the southern heavens there is a group containing a multitude of stars, all blue. It is impossible, therefore, to suppose that the blue colours seen in multiple systems are due to the mere effect of contrast. In some cases this may happen, however; or at any rate the effect of contrast may intensify the colours of each component of a "complementary double." There is one very charming instance of complementary colours in a double star which may be separated with a telescope of very low power. We refer to the star Albireo on the beak of the Swan. The components of this star are orange and blue, the tints being well pronounced. It has been found that when one of the components is hidden, the other still preserves its colour, though not quite so distinctly as when both are seen together. Another "complementary double" is the star Andromeda. The primary is red, the smaller star green. In very powerful telescopes the smaller component is found to be itself double, and doubts exist among astronomers whether the two minute components of the lesser star are both green, or one blue and the other yellow. There is another double star very beautiful in a powerful telescope. This is the star Bootis, on the Herds man's belt; it is called also Mirach, and, on account of its extreme beauty, Pulcherrima. The components are nearly equal-one orange, the other a delicate emerald green. One of the most startling facts revealed by the careful observation of the fixed stars is that their colour is not unchangeable. We may begin at once with the brightest of the fixed stars-Sirius. This star was known to the ancients as a red star. To its fiery hue may doubtless be ascribed the peculiar influence assigned to it by ancient astronomers. At present Sirius is brilliantly and unmistakeably white. We have not such decisive evidence in the case of any other noted star. But among telescopic stars, there have been some very remarkable changes. There are two double stars, described by the elder Herschel as white, which now exhibit golden-yellow primaries and greenish satellites. That careful observer, Admiral Smyth, records also that one of the components of a double star in Hercules changed, in twelve years, from "yellow, through gray, cherry red, and egregious red, to yellow again." The questions may well be asked: Whence do the stars derive their distinctions of colour, and by what processes do their colours, change? To these questions modern discoveries have supplied answers which, if not complete, are well worth listening to. It had long been suspected that the stars are in reality suns. It had been shown that their distance from us must be so enormous as to enable us to assign to them an intrinsic brilliancy fully equal, in some instances, and in others far superior, to that of our own sun. Nothing remained but that we should have some evidence that the kind of light they emit is similar to that which we receive from the sun. This evidence has been supplied, though only of late years. We cannot bere enter at length into an account of the important discoveries of Kirchhoff and Bunsen, which have enabled astronomers to analyse the light emitted from the celestial bodies. It will be sufficient to remark that in the solar spectrum there are observed fine dark lines breaking the coutinuity of the streak of light, and that these lines have been proved to be due to the presence of the vapours of certain elements in the solar atmosphere. The proof depends on the exact correspondence of numbers of these lines, grouped in a complex manner (so as entirely to eliminate the possibility of a mere chance accordauce) with the bright lines seen in the spectra of light from the vapours of those elements. When once Kirchhoff and Bunsen had proved the possibility of exhibiting the same set of lines either as bright lines on a dark ground or as dark lines on a brilliant spectrum, all doubt as to their meaning in the solar spectrum disappeared at once. It has been found that in the sun's atmosphere there are present the vapours of iron, copper, zinc, and nickel, besides calcium, magnesium, sodium, and other metals. But the vapours of tin, lead, silver, and gold do not appear to be present in the solar atmosphere. One of the most remarkable dark lines is due to the presence of hydrogen. But it has been found possible to extend these Let us take first the brilliant Sirius. This star The atmosphere around Sirius contains sodium, The whole spectrum is covered by a very large number of faint and fine lines, indicating a corresponding variety in the substances vapourised in the star's atmosphere. The hydrogen lines are abnormally strong as since it is a peculiarity characteristic of white stars Take next an orange-red star, the brilliant Betel- Take next the yellow star, Pollux. The observers yellow stars are characterised by the absence of The observations required, says Dr. Huggins, “are We recognise, then, the influence of time upon But, inasmuch as it resulted from Dr. Huggins' examination of a temporary star which appeared last year, that the increase of light-for it was only the abnormal brilliancy of the star which was really temporary-was due to a sudden outburst of inflamed hydrogen, it seems on the whole more probable that the incandescent vapours of stars buru with variable brilliancy, than that they vary in quantitative distribution. As regards the constant colours of different stars, we are enabled at any rate to deduce negative results. For instance, we may dismiss at once the theory started some years ago by the French astronomer M. Doppler. He supposed that the colours of & star are due to the proper motions of the star, acting so as-in effect-to lengthen or shorten the waves of light proceeding from the star to the earth, just as the apparent breadth of sea-waves would be greater or less to a swimmer according as he swam with or against their course. It is quite clear that the effects of a motion rapid enough to produce such a change would be to shift the position of the whole tected by a reference to the spectral lines. Apart spectrum,-and this change would be readily defrom this, the colour of a star would not be changed by such motion, the spectrum being merely displaced, not affected in its characteristics of colour. (See p. 275.) Another theory-that the orange and red tints indicate a lower degree of temperature must also be dismissed. For we have seen that the spectra of red stars indicate the presence of the vapour of iron and other metals, and nothing but an exceedingly high temperature could vapourise these. It seems clear that the difference of tint is due to the different arrangement of the dark lines-in other words, to an absolute difference of physical constitution. "There is a striking difference," remarks Huggins, between the effect on the colour of a star of such closely grouped and very dark lines in the green and blue part of the spectrum of Betelgeux, and of the corresponding part of the faint, and wholly unequal to produce any noticeable spectrum of Sirius, in which the dark lines are subduing of the blue and green rays." But we have still to consider the peculiarities presented by the double stars. We have seen that *I may be permitted to notice that this was among the earliest published references to the possibility of decr mining motions of recess or approach by the displacement of the spectral lines. Very shortly afterwards, Dr. Huggins had succeeded in applying the method, which he had been endeavouring to do for some month before. I was, however, quite unaware of this when I wrote the above lines. I believe, in fact, his rescarolom were carried on altogether privately. |