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mutter of smallpox and scarlet fever is particularly persistent. Clothes which had belonged to some uuo suffering from smallpox, and been laid by for months, have passed on the complaint to thoee who have had the misfortune to handle them. The poison of scarlatina is most difficult to eradicate, chiefly fmtn the desquamation or peeling off of the skin, which occurs when the malady is passing away, and which is the chief medium for the dissemination of the contagious matter. The skin or cuticle comes off in very fine powder, which is extremely light, and penetrates into every corner of the room which dust can reach, accumulating on the cornice of the door, on the shelves of bookcases, or projecting parts of picture frames. The clothes which the sick man has worn are a frequent medium of contagion ; it has been noticed that they have been sent for miles to people who were quite ignorant of the fact that they cam:1 from an infected place, and yet have communicated the contagion. Woollen clothes retain the infectious material much more than cotton, for the obvious reason that wool, from its structure, is much more likely to absorb the poison than cotton. Black clothing also retains the contagious material for a longer time than white; this fact is quite unexplained. It was first noticed at the military hospitals in Vienna, where it was found that when я soldier with a white uniform had recovered from an infectious disease, and was sent hack to the barracks, fewer admissions into the hospital were made of his fellow-soldiers, suffering from the same disease, than when the patient's uniform had been of a dork colour.

The bed clothes and bedding, from the wool and hair which they contain, offer a Urge surface for the reception ami retention of the contagious material. The carpets and curtains are frequently sources of contagion, because seldom disturbed. Drinking-water also conveys the infection; the emanations from the sick man, the water in which he has washed, Ac, are too often thrown carelessly away, and unless properly disinfected, the contagions material may find its way into wells and cisterns, and thus spread the disease. Typhoid fever, which destroys on an average 10,000 people in the prime of life, every year in England, is almost solely propagated by the drinking water, as it is very slightly contagious to those who nurse or tend the sufferers. Dr. Snow, in his work "On the Mode of Communication of Cholera," has proved most conclusively that cholera is chiefly communicated by the drinking water, and but seldom through the ordinary means of infection. To conclude this subject, it niUHt not be forgotten that each specific disease has its own specific germ. The poison of small-pox will not produce measles, but only smallpox; and an attack of small-pox offers no pi otection whatever against measles.

When the contagious matter meets with an individual in a condition favourable to the production of the disease (for, like the seed, the contagious matter must be placed in a fit soil before it can germinate), the individual thus attacked does not at once show symptoms of illness, nor indeed does he know that he is going to be ill, but there is always an interval, usually many days, between the reception of the poison, and the first feeling of malaise. This stage is called the stage of incubation, in which the disorder is latent within the patient ; for there are no signs or symptoms by which it can be known that he retains within him the seeds of severe illness ; he goes about his ordinary occupations, und feels quite in his usual health. This period of incubation varies in different illnesses; in small-pox and measles it is twelve or fourteen days; in scarlet fever it lasts from five to twelve days, never being less than five, or more than twelve, in duration. The knowledge of this fact may often be of practical use ; if a child have been, by chance, to see another who has taken the measles or scarlet fever, the mother would know that all risk of the infection woidd be over in about a fortnight from the time of the visit. For this reason it is that travellers are detained so long a time in quarantine, lest any of them might he in the incubative stage of an epidemic.

The end of the stage of incubation is announced when the person begins to feel ill ; what is called the stage of invasion has arrived, and this is the commencement of the illness properly so called; like the stage of incubation, this has a course of a certain number of days, varying in each disease. In scarlet fever the invasion-stage lasts only twentyfour hours, and is accompanied by feverishness and sore throat ; in small-pox it lasts forty-eight hours, and there is also a great pain in the back, and the patient feels seriously ill. In measles this stage lasts three days, during which the child is feverish, and its eyes and nose pour out a fluid, which scalds the skin over which it flows. In whooping-cough, the stage of invasion lasts nearly a fortnight, during which time the child seems to have only an ordinary severe cough, without anything to announce its specific character. When the complaint is in the stage of invasion, no drug or medicino is known which has the least power to stop the illness from going on further into the ypecific stage, which, like the two preceding stages, has a sharply defined duration, beyond which it

never lasts, and within which it never terminates, except by the death of the patient. The tendency of this stage is to end, after its specific duration, in the complete recovery of health. In no complaint is tliis better exemplified than in typhoid fever. Here the specific illness never lasts less than twenty-eight or more than thirty days; during this time the patient is feverish, with a temperature of the body often rising to 1U6J Fahr., and is delirious and entirely without appetite. If the patient only survive the twenty-eighth or thirtieth day, the fever and delirium go, the temperature of the body falls to the natural standard, 98* Fahr., and the appetite begins to return. This illustrates what was said about the power of curing disease, and the importance of an intimate acquaintance with its natural history. Here the physician is aware that he cannot cure, but at the same time he knows that if he can keep his patient alive over a certain day, the patient will recover; the only endeavour of the physician in this case is, then, aknply to prolong life, to enable the patient to live over the critical day, and thus by simply endeavouring to prolong life, the physician often succeeds in на ring life.

In this specific stage there are two symptoms, the specific process, and fever. In small-pox and measles, the specific process is the rash on the skin; in scarlatina, the rash on the skin, and the sore throat conjoined ; while in diphtheria it is the sore throat alone, which is the specific process. This specific process is the essence of the whole disease, without which the disease could not exist, and the means by which the disease is propagated. The specific process itself is strictly local, never affecting all the tissues of the body generally, but limiting itself to one set of tissues, or to those analogous to it. Thus iu small-pox, the local specific process is limited to the skin alone, except when it attacks, in grave cases, the mucous membrane, similar in structure to the skin, of the windpipe and air-tubes of the lungs. In diphtheria, the mucous membranes alone arc involved, while in typhoid fever it is the adenoid tissue, which the spleen and some other organs largely contain, that is affected. Fever is a constant accompaniment of the local specific process ; and by fever we simply mean that the temperature of the body, as measured by the thermometer, is greater than in health. The natural temperature of the body is 98° Fahr., but in fever it rises above this. The temperature of the body in health is maintained by a constant oxidation or burning of the tissues by the oxygen of the air, brought by the blood from the lungs. In fever, this process of combustion goes on more rapidly, and the tissues are burnt away at a higher rate, and thus an elevation of temperature is produced. A great increase in the products of combustion, wluch are eliminated from the system, takes place during the fever, or at its termination. This process of increased combustion readily explains the rapid emaciation which occurs in fevers. The great debility of the patient depends upon the exhaustion produced by the high temperature. According to Joule's law, every degree of increased temperature represents a certain amount of mechanical exertion. The Rev. Professor Haughton says: "The work due to animal heat would lift the body through a vertical height of eight miles per day; and it thus appears that an additional amount of work, equivalent to the body lifted through one mile per day, is spent in maintaining its temperature at fever heat. If you could place your fever patient at the bottom of a mine, twice the depth of the deepest mine in the duchy of Cornwall, and compel the wretched sufferer to climb its ladders into the open air, you would subject him to less torture from muscular exertion, than that which he undergoes at the hand of nature, as he lies before you, helpless, tossing, and delirious on his fever couch."

{To he concluded next week.)

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Part Ш.


[Concluded from page 391).

IT is well known that certain organisms of the animal world do not confine themselves to one state of being or to one order of existence, and the most familar instance of this roving habit is the caterpillar, which passes first into the chrysalis state, and after that into the butterfly. This habit is not, however, peculiar to the organic world; for energy delights in similar transmutations, and we have just seen how the eminently silent and invisible electrical current may occasionally be transmuted into the vivid, instantaneous, awe-inspiring flash of lightning. Nor is this element of change confined to our peculiar corner of the universe, but it extends itself to remote starry systems, in some of which there is a total extinction of luminosity for a while, to be succeeded by a most brilliant outburst, presenting all the appearance of a world on fire.

We shall not enter here into great detail regarding the various changes of energy from one form into

By Balfour Stewart, in Nature.

another; suffice it to say that among all these changes of form, and sometimes of quality, the element of quantity remains the same. Those of our readers who are mathematicians know what is meant by variable quantities, for instance, iu the equation *+.'/+;=A, if x, y, and % are variable and A constant, you may change x into у and into ;, and у into x and into г, and in fact, perform any changes you choose upon the left hand side of your equation provided that you keep their sum always constant and equal to A. It is precisely thus iu the world of energy ; and the invariability of the sum of all the energies of the universe forms the doctrine known as the "conservation of energy." This doctrine is nothing else than an intelligent and scientific denial of the chimera of perpetual motion.

Recognizing the great importance of work, it was natural enough at an early stage of our knowledge that enthusiasts should endeavour to create energy or the power of doing work—that is to say, endeavour to construct a machine that should go on working for ever without needing to be supplied with fuel in any way—and accordingly, inventors became posessed with the idea that some elaborate system of machinery would, no doubt, give us tliis grand desideratum, and men of science have been continually annoyed with these projects, until in a moment of inspiration they conceived the doctrine of the conservation of energy.

It flows from this doctrine that a machine is merely an instrument wliich is supplied with energy in one form, and which converts it into another and more convenient form according to the law of the machine.

We shall now proceed to trace the progress of energy through some of its most important transformations. To begin with that one to which we have already alluded, What becomes of the energy of a falling body after it strikes the earth? This question may be varied in a great number of ways. We may ask, for instance, What becomes of the energy of a railway train when it is stopped ? what becomes of the energy of a hammer after it has struck tie anvil ? of a cannon ball after it has struck the target? and so on.

In all these varieties we see that either percussion or friction is at work; thus it is friction that stops a railway train, and it is percussion that stops the motion of a falling stone or of a falling hammer, so that our question is in reality, what becomes of the energy of visible motion when it has been stopped by percussion or friction?

Rumford and Davy were the pioneers in replying to this important question. Rumford found that in the process of boring cannon the heat generated was sometimes so great as to boil water, and he supposed that work was changed into heat in the process of boring. Davy again melted two pieces of ice by causing them to rub against each other, and he likewise concluded that the work spent on this process had been converted into heat.

Wo see now why by hammering a coin on an anvil we can heat it very greatly, or why on a dark night the sparks are seen to fly out from the break-wheel which stops the motion of a railway train, or why by rubbing a metal button violently backwards and forwards against a piece of wood we can render it so hot as to scorch our hand, for in all these cases it is the energy of visible motion which is being converted into neat.

But although tliis was known nearly a century ago it was reserved for Joule, an English philosopher of the present day, to point out the numerical relation subsisting between that speeies of energy which we call visible motion and that which we call heat.

The result of Ids numerous and laborious experiments was, that if a pound of water be dropped from the height af 772ft. under the influence of gravity, and if the velocity which it attains be suddenly stopped and converted into heat, this heat will ' be sufficient to raise the whole mass 1 Fahr, in temperature.

From tliis he concluded that when a pound of water is heated V Fahr, in temperature, an amount of molecular energy enters into the water which is equivalent to 772 foot-pounds, that is to say, to lib. raised 772ft. high against the influence of gravity or allowed to fall 772ft. under the same influence.

He found again that if a pound of water were to fall twice this distance, or l,S44ft. under gravity, the velocity, if stopped, would raise its temperature 2' Fahr., and in fact that the riso of temperature under such circumstances is proportional to the height from which the pound of water is supposed to fall. By this means an exact relation is established lietween heat and work. Grove was the first to point out the probability of a conueetüm between the various species of molecular energy ; anil the researches of Joule, Thomson, and others, have established these relations with numerical accuracy. No better example of the correlation of the various kinds of energy can be given than what takes place in a galvanic battery. Let us suppose zinc is the metal used. Hero the source of energy is the burning or chemical combination of the zinc with oxygen, &c, in order to form a salt of zinc. The source of energy is in fact much the same as when coal is burned; it is the energy produced by chemical combination. Now, as we have said, the zinc combines with the oxygen and sulphate of zinc is produced, but the result of this combination docs not at first exlubit itself in the form of heat, hut rather in the form of an electric current. No doubt a great portion of the energy of this electric current is ultimately spent in heat, but we may, if we choose, spend part in promoting chemical decomposition; for instance, we may, decompose water. In this case part of the energy of the battery, derived, as has been stated from the burning of the zinc, is spent in heat, and part in decomposing the water, and hence we shall have less heat than if there were no water to decompose. But if when we have decomposed the water, we mix together the two gases hydrogen and oxygen which are the residts of this decomposition, and explode them, we shall recover the precise deficiency of heat. Without tho decomposition, let us say that the burning in tho battery of a certain weight of zinc gives us heat equal to 100, but with the decomposition only 80 ; twenty units of energy have therefore become spent in the decomposition, but if we explode the mixture of gases produced from the decomposition we shall get back heat equal to 20, and thus make the whole result of the burning of the zinc 100 units of energy as before.

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In like manner, if our electric battery is made to do work, thus forming a kind of engine, we shall have the heat produced by the current diminished by the exact equivalent of the mechanical effect which we have obtained from this engine.

There is nothing for nothing in the universe of energy.

By Captain John Ekicsson.

IN a previous communication on this subject,* I adverted briefly to some experimental engines which I have constructed in order to ascertain the practicability of employing solar heat as a motive power. I also adverted to the imperfections of the methods adopted by certain physicists to determine the dynamic energy of the sun's radiant heat. Having in the mean time perfected the necessary instruments for measuring, with desirable precision, the dynamic force of solar heat under the varying conditions governed by the changes of altitude, seasons, atmospheric temperature, and the presence of aqueous particles in the air—elements of paramount importance in judging of the applicability of the sun's radiant heat as a motor—I intend to lay before the readers of Engineering a series of articles giving a brief account of my researches, to be accompanied by accurate illustrations of the instruments employed.

Apart from ascertaining the dynamic energy of solar radiation by accurately measuring the units of heat developed in a given time under the varying conditions adverted to, I have extended my labours to the determination of tho true intensity of the son's radiant heat. Accordingly, I have instituted a serios of observations which enable me to estimate the loss of intensity during the passage of the raye through the atmosphere. By adding this to the

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ascertained intensity of the radiant heat on reaching the surface of the earth, and before it is affected by terrestrial radiation, I can determine the actual intensity at the point where the rays enter the earth's atmosphere. My attention was originally called to the important subject of actual intensity of solar radiation by reflecting on the limited amount of dynamic energy, about five units of heat per minute upon an area of 142 square inches, exposed perpendicularly to the sun's rays, while the thermometer idicated 150' above Fahrenheit's zero, or 610° above absolute zero. Preliminary experiments, conducted very carefully, having disclosed the startling fact that the real intensity of solar radiation marks a point on the thermometric scale several hundred degrees below the freezing point of water, I resorted to the expedient of concentrating the sun's rays by such a method that the degree of concentration could be accurately measured. Investigations, conducted in conformity with this method of determining the true intensity of the radiant heat, proved the temperature to be nearly identical with that shown by the preliminary experiments referred to. The extraordinary fact "was accordingly established, that the intensity of the sun's rays before gaining by terrestrial radiation, is so feeble that fluid mercury contained in an exhausted shallow vessel covered with a thin lens of about 50in. focus, and exposed to the full power of a clear sun, will very rapidly become solid, provided the vessel is pre* vented from receiving heat from surrounding substances. It matters little whether the molecular action within the mass of mercury necessary to keep it in a fluid state is checked by the slower undulations of the solar ray, as waves of a rapid motion are checked by mingling with waves of less motion; or whether the molecular action within the mass of mercury is communicated to the surrounding cold vessel. In either case the reduced molecular force within the freezing mercury proves the inadequacy of the action produced by the sun's rays to maintain the metal in a fluid state.

Incidentally the experiments thus instituted to demonstrate the feeble power of solar radiation beforo its intensity is augmented by the intervention of the earth's atmosphere have established the fact that tho вш-face of the moon, lieing devoid of any gaseous envelope, is at all times, even under the vertical вип of the long lunar day, intensely cold. This apparently irrelevant subject will be considered hereafter. In the mean time, illustrations and descriptions will be presented of the instruments by means of which it has been satisfactorily demonstrated that before the temperature is augmented by the accumulation of heat which results from terrestrial radiation and the presence of the atmosphere, the sun's radiant heat, as before stated, marks a point on the thermometric scale several hundred degrees below the freezing point of water.

Before entering on a description of the accompanying illustration of my solar calorimeter (a denomination adopted in preference to "actinometer," as its object is only that of measuring the amount of heat transferred from tho sun to the earth), I deem it proper to say that I object to the inferences which Pouillet, Mayer, and others have drawn from our knowledge of the dynamic force of

solar radiation on a given surface of the earth Unquestionably the amount of heat transferred froK the sun to the earth may be accurately computed bj means of the eolar calorimeter; but to infer fra« the point thus estabbshed that the sun parts wit! as great an amount of heat in all directions on e¿ equal area as that which the earth during it« orbiUI motion receives by intercepting and Bucceasivelv arresting the solar wave is a mere gratituous assumption. The practical mind refuses to accept i theory which involves such a vast disproportion lietween the means and the end, as the assrumptioa that 200,000,000 times more heat is wasted than tha: wliich is employed to animate the planetary worldof our system, more especially as the improbable and extravagant, not to say absurd, speculations which have been put forth by Mayer, Helinholtz, and others, all fail to suggest any mode of supplying the assumed enormous waste which does not iK>int to & speedy extinction of the central force. I will return to tills subject on a future occasion, when tbe consideration of the new motor, the solar engine, will be in order.

M. Pouillet's pyrheliometer being now generally known through Professor Tyndall's work on " Heat as a Mode of Motion,'' the imperfections of that instrument may be pointed out without minutely describing the method adopted by the French physicist in determining the amount of dynamic force which the earth receives from the sun in a given time. The radical defect of Pouillet's instrument is, that it cannot be nsed during winter when the thermometer is below the freezing point, as warm water would have to be used, in which case the loss of heat by radiation and convection would be so great as to render the task futile of accurately measuring the force of solar radiation. This defect of Pouillet's method is the more serious as the Leai of the sun is most intense during the winter solstice for given zenith distances, not only on account of the diminished distance between the sun and the earth, but owing to the fact that the sky is clearer during a cold winter's day than during the heat oí summer when the air is charged with vapour.

The loss of heat by radiation, in the pprhetiameter—loss of heat by convection, accelerated igt currents of air—the absence of adequate means /or circulating the fluid contained within the heater— the rude method of keeping the inslranwut perpendicular to the sun by hand—not to mention Üie 4isturbing influence of respiration and the ríAUÜoii from the operator's body—are self-evident delects. Nor can we pass unnoticed the want of any direct means of ascertaining the depth of the atmosphere through which the radiant heat passes at the moment of measuring its energy. I need scarcely point out that computations based on latitude, daU, and tract time, are too complex and tedious for investigations in which the principal element, the depth of the atmosphere, is continually changing.

It will be well to state at the outset that the solar calorimeter, and all my instruments constructed for investigating the mechanical properties of solar heat. are attached to a table which swings upon a horizontal axle, and which rotates round a vertical pivot. appropriate mechanism being applied for regulatim; the combined vertical and lateral movement in such a manner that the top of the table, composed of a heavy brass plate accurately faced, is at all turns during observations kept perpendicular to the central ray of the sun. Hence, instruments, whose base is at right angles to their vertical axis, niay I* secured at any point of the face of the rotating tabic without further adjustment. A graduated arc U attached to one end of this table, provided with an immovable index; consequently, the sun's zenith distance may at all times be ascertained by a mere inspection, a very great convenience in an investigation which at every instant is dependent on the changing depth of the atmosphere through which the sun's rays pass. As this depth bears a fixed relation to the sun's zenith distance, it may of course be accurately determined by noting the position the fixed index on tbe graduated arc; but as then' is no time during investigations of this kind for сокputи t toi is, as already pointed out, I ha vc constructed a graduated scale provided with n movable nuM index, which, by being brought to the division corresponding with the observed zenith distance, shows the depth of atmosphere. It is proper to observe that in constructing this »cole I have assumed the earth to be a perfect sphere of 3,956 miles radius. The error resulting from this assumption is, however, so trifling, that the described graphic method of ascertaining the depth of the atmosphere may, without appreciable discrepancy, be employed in all latitudes. The solar calorimeter consists of a double vessel, cylindrical at the bottom, and conical at the top, an 8in. lens being inserted at the wide end in the manner shown by the illustration above. The interior is lined throughout with burnished silver, and the space between the two vessels w closed at the top and bottom by means of perforated rings, as shown in the transverse section, the object being to distribute equally a current of water to l>e passed tlirough tho space between the vessels. Nozzles are applied at the top and bottom of the external vessel of suitable form to admit of sninu hoses being attached. A stop-cock with courhng joint is applied at the bottom, communicaüBÍ

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with the interior of the calorimeter, and connected with an air pump for exhausting the same. A cylindrical vessel, termed heater, with curved top and bottom, composed of polished silver, is secured in the luwer part of the instrument, and provided with a conical muzzle at the top, through which a thermometer is inserted from without. Within the lower part of the heater is introduced a centrif agal paddle wheel, surrounded by a cylindrical casing divided in two compartments by a circular diaphragm, the lower compartment containing four radial wings or paddles, the diaphragm being perforated in the centre. The centrifugal paddle wheel revolves on an axle which passes through a stuffing box applied at the bottom of the double vessel, the rotary motion being imparted by means of a pulley secured to the lower end of the axle. The operation of this wheel, intended to promote perfect circulation of the fluid within the heater, is quite peculiar. It will be readily understood that by turning the wheel the centrifugal action of the fluid produced by the rotation of the paddles will draw in water downwards through the central perforation of the diaphragm, and force the same into the annular space round the casing of the wheel; thus an upward current will be kept up through tliis annular space uniform on all sides. This current, after reaching the top of the heater, will toen return, first entering the open end of the casing of tho wheel, and ultimately the central perforation of diaphragm. I have been thus particular in describing this system of promoting uniform circulation within the heator because a proper proportion of the actual mean temperature of tho water contained in the same is the aU important condition on which depends the accuracy of tho determination of the number of units of heat developed. It only remains to be pointed out that the lens, whirl) is so proportioned as to admit a sun beam of 52 square inches of section, is placed at such a distance from the heater that when the concentrated rays reach the upper end (painted with lamp-black) they are confined to an area of 3'25 square inches, precisely l-16th of the sectional area of the sunbeam which enters the lens.

It will be obvious that the concentration of the radiant heat on an area of only one-sixteenth of that of the section of the sunbeam, removes a very difficult disturbing element from the investigation— viz., the great amount of heat radiated by the blackened surface of the heater, which, in the pyrhcliometer, is sixteen times greater than in the solar calorimeter. But this is not all, while tho sixteen times more extensive blackened surface of the former is exposed to currents of air, the disturbing effects of which can neither be controlled nor computed, error arising from convection is wholly removed from the latter, because the reduced blackened surface of the heater receives the concentrated radiant heat within a vacuum. The loss of heat at the bottom and sides of Fouillet's instrument, caused by convection and currents of air, is likewise wholly removed in the solar calorimeter by the expedient of operating within a vacuum. It will be seen, therefore, that the loss of heat by convection and currents of air has been wholly ob

viated in the solar calorimeter, while the loss caused by radiation from the blackened surface of the heater has been reduced to a mere fraction. It may be contended, however, that the loss by radiation of the polished heater against the interior polished surface of the calorimeter, although minute, is yet appreciable; and thut some heat will be lost by conduction at the points where the heater joins the external vessel. Even these trifling sources of error, it will be seen presently, have been removed by the new method. A force pump and capacious cistern containing water ore arranged near the calorimeter, a uniform temperature of 60° being kept in this cistern by the usual means of a warm and cold water supply. By appropriate hose and the force pump mentioned, a constant current is kept up through the space between the internal and external casings of the instrument; hence, every part of the latter may be brought to a uniform temperature of 60" in a few minutes. The process of measuring the solar energy is conducted in the following manner: The thermometer being withdrawn, the heater is charged with distilled water of a temperature of about 45°, after which the thermometer is again inserted. The table supporting the instruments should now be turned towards the sun and the paddle wheel put in motion. The indication of the thermometer must then be watched, and the time accurately noted when the mercurial column marks 60° on the scale, the observation continuing until tho thermometer marks 70°, at which point the time is again accurately noted. The experiment being then concluded, the table should be turned away from the sun. It scarcely needs explanation, that during the elevation of the temperature of the water from 50s to60° the instrument radiates towards the heater, and that while the temperature rises from 60° to 70°, the heater radiates towards the instrument. In each case the amount of beat radiated, that is, the gain and the loss, is almost inappreciable, since both the heater and the surrounding internal vessel ore composed of polished silver. The amount of gain and loss of heat by conduction at the points where the heater joins the eurromiding vessel, if appreciable, evidently balance each other in the sumo manner as the gain and loss by radiation.

The weight of distilled water at 60° contained in the heater, and the weight and specific heat of the materials which compose its parts, being ascertained, the number of units of heat necessary to elevate the whole 20° may be readily calculated. To this must bo added the percentage of calorific energy lost during the passage of the sun's rays through the lens. The eun will represent a permanent coefficient for each particular instrument which may ever afterwards be employed to determine the dynamic energy of tho sun*s radiant heat. Obviously the indication will be equally correct during the winter solstice in a northern latitude with the mercurial column at zero as during the summer solstice within the tropics, when the thermometer marks 100° in the shade.

It must not be supposed that the some difficulty presents itself in ascertaining the loss of calorific

energy of tho rays of heat as that involved in ■ determination of the retardation which rays of light suffer during their passago through a lens. In order to determine the former we have only to compare the units of heat developed by the direct action of a sunbeam of a given section, with the number of units developed by another sunbeam of eqnal section during an equal interval and at the same time, acting through the lens, the retarding influence of which we desire to ascertain. I have constructed an instrument for this purpose by means of which the diminution of the calorific energy of the sun's radiant heat can be accurately measured for all lenses not exceeding f* Jin. diameter. This instrument will be delineated and explained at tho proper time.

Keferriug to the experiments which have been made with the solar calorimeter, it is specially worthy of notice that the sun's energy, as shown by this unerring mode of measuring the force actually transferred to the surface of the earth, i , never regular. The force of the radiant heat (call it molecular action) indicated by the increment of the temperature of the fluid in tie heater of the instrument, is continually oscillating. At first I attributed this circumstance to invisible masses of light vapour passing through the atmosphere. More recent observations induce me to think that wont of constancy in the evolution of the heat at the source may possibly be the true cause.—Engineering.

New York, June 21.


{Continued from pace 892.)

í)í)A Boot's double-reciprocating or equate /v^rti piston engine. The "cylinder," A, of this engine is of oblong square form and contains two pistons, В and C, the former working horizontally, and tho latter working vertically within it; the piston, C, is connected with the wrist, a, of the crank on the main shaft, b. The ports for the admission of steam are shown black. The two pistons produce the rotation of the crank without dead points.

225. One of the many forms of rotary engine. A is the cylinder, having the sbaf t, B, passing centrally through it. The piston, C, is BÜnply an excentric fast on the shaft and working in contact with the cylinder at one point. The induction and eduction of steam take place as indicated by arrows, and the pressure of the steam on one side of the piston produces its rotation and that of the shaft. The sliding abntmeut, D, between the induction and eduction ports moves out of the way of the piston to let it pass.

226. Another form of rotary engine, in which there are two stationary abutments, D, D, within the cylinder, and the two pistons, A, A, in order to enable them to pass the abutments, are made to slide radially in grooves in the hub, C, of the main shaft, B. Tho steam acts on both pistons at once, to produce the rotation of the hub and shaft. The induction and eduction are indicated by arrows.

227. Another rotary engine, in which the shaft, B, works in fixed bearings excentric to the cylinder. The pistons, A, A, are fitted to slide in and out from grooves in the hub, C, which is concentric with the shaft, but they are alwaye radial to the cylinder, being kept so by rings (shown dotted) fitting to hubs on the cylinder-heads. The pistons slide through rolling packings, a, a, in the hub, G.

228. The india-rubber rotary engine, in which the cylinder has a flexible lining, E, of india-rubber, and rollers, A, A, are substituted for pistons, said rollers being attached to arms radiating from the main shaft, B. The steam acting between the indiarubber and the surrounding rigid portion of the cylinder presses the india-rubber against the rollers, and causes them to revolve around the cylinder and turn the shaft.

229. Holly's patent double-elliptical rotary engine. The two elliptical pistons geared together are operated upon by the steam entering between them, in such manner as to produce their rotary motion in opposite directions.

These rotary engines can all be converted into pumps.

230. Overshot water-wheel.

231. Undershot water-wheel.

232. Breast-wheel. This holds an intermediate place between overshot and undershot wheels; haa float-boards bio the former, but the cavities between are converted inte buckets by moving in a channel adapted to circumference and width, and into which water enters nearly at the level of axle.

233. Horizontal overshot water-wheel.

234. A plan view of the Fourneyron turbine water-wheel. In the centre are a number of flxed curved "shutes" or guides, A, which direct the water against the backets of the outer wheel, B, which, revolves, and the water discharges at the circumference.

235. Warren's central discharge turbine, plan view. The guidée, a, are outside, and tlie wheel, o, revolves within them, discharging the water at the centre.

236. Jonval turbine. The "shutes" are arranged on the outside of a drum, radial to a common centre and stationary within the trunk or casing, b. The wheel, c, is made in nearly the same way; the buckets exceed in number those of tho shutes, and are set at a slight tangent instead of radially, and the curve generally used is that of the cycloid or parabola.

237. Volute wheel, having radial vanes, я, against which the water impinges and carries the wheel around. The scroll or volute casing, 6, confines the water in such a manner that it acts against the vanes all around the wheel. By the addition of the inclined buckets, с, c, at the bottom, the water is made to act with additional force as it escapes through the openings of said backets.

238. Barker's or reaction mill. Rotary motion of central hollow shaft is obtained by the reaction of the water escaping at the ends of its arms, the rotation being in a direction the reverse of the escape.


AN interesting lunar region, that has been very inadequately described, is found on the northern hemisphere of the Moon, between the well-known spot Piato and the lowest edge or limb of the Moon as seen in an inverting telescope. This region, which is situated between the craters Fontenelle, Timteus, and Epigenes, of Beer and Madlcr, comes into sunlight about and just after the first quarter. Beer and Midler speak of it as calculated to "throw the observer into the highest astonishment,'1 and certainly as the San rises upon it and illuminates one after another the ridges of mountains which compose it, it is a magnificent spectacle. The three leading objects, the craters above-named, which may easily be found by means of Webb's index map in his" Celestial Objects for Common Telescopes," are the three angular points of the region. It is naturally divided into two distinct areas, and is bounded on the south by the Mare i'r^joris. The western division consists of very nigged land, the principal feature being a bold promontory, more or less cleft, which stretches into the Mare Frigoris towards Plato. Between the rugged land on the west, and a very individualized depressed surface on the east, a sinuous mountain-chain extends from the promontory above-named to the fine bold eastern portion of the rim of Epigenes. This crater is an interesting instance of a feature by no means uncommon on the Moen, riz., portions of wailed plains occuring in extensive lines of cliffs or mountains. In many instances the cliffs are interrupted or broken, so as to form extensive bays on the surfaces of the plains and bold promontories at the points of their inosculation. The west border of Epigenes forms a portion of another range, west of and nearly parallel with the before-mentioned chain of moun

tains. Tho western rango rises to a considerable altitude on the west border of Epigenes, and is continued to a high mountain at tho west end of a flue walled plain just west of the crater Anaxagoras. This plain is surrounded by high mountains, and is by far the grandest and most imposing object in thia lunar landscape. It remained unnamed until the late Dr. Lee suggested the designation "Goldschmidt " аз suitable for it. The eastern division of this region—which, as before stated, consists of a depressed surface—is not mach raised above the surface of the Mare Frigoris on the south. The N.E. boundary forms a separation between two levels, as if a "fault" had occured in the line between Fontenelle and Epigenes. The lower level, which has upon it two short mountain arms stretching outwards from the N.E. boundary of the depressed surface, extends towards Anaxagoras, and is generally smooth. There is in its neighbourhood a well-marked crater forming a triangle with the N.E. angle of the depressed surface east of the rugged land and Fontenelle. Between this crater and Fontenelle an imperfect elliptical depression exists, and another may be noticed to the N.E. of this. Between the craters Tinnens, Fontenelle and Anaxagoras, the observer will find three very' distinctly marked and individualized formations, viz., the rugged land west of the mountain chain passing through the east border of Epigenes; the depressed surface on the east of the same mountain chain (the interior of this depressed surface contains several interesting objects); the third formation is the depressed surface extending towards Anaxagoras. To trace out these features, to observe during the progress of the illumination of the northern parts of the Moon's disc the changes in aspect which they undergo as the Sun rises higher above them, and as that hitherto unexplained and mysterious metamorphosis, which so gradually creeps over the surface, obliterating some objects and bringing out other» not seen before, passes through its various phases, together with the gradual streaking of the landscape with the rays from Anaxagoras, form a pleasing and instructive occupation with the telescope while the Moon is passing from her first quarter to full; and to those students who prolong their watching» to "early dawn " the formations seen under the reverse light are full of interest.

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THERE is probably no branch of mechanical science which has of late years received so comparatively small a share of study or made so little progress in this country as horology.

To advocate the sudden adoption of such reforms as would to any great extent alter the character of the article produced, or revolutionize the present system of hand-finishing by the piece, would not be wise, but without going to this length there is room for vast improvement and much economy to be effected in the manufacture. At present every movement maker uses a different gauge (which he does not understand), and adopts a different calliper, based on bis individual experience, the residt of winch is that there will be nearly as much difference in the same nominal sizes of two different makers as there is supposed to be difference between two consecutive sizes of watch movements. We say advisedly "supposed" difference, because the actual difference is not even established, and is as variable as the gauges generally made use of, which have an unmarked and undefined space of varied length, and give a result whicli cannot be definitely expressed by any known scale of measurement. The approximate difference, however, between the diameter of consecutive sizes of watch frames of the same make will be found to be '07, or about the fourteenth part of an inch, which difference is so small that the various sizes of movements in finished watches are not readily determinable, and a greater multiplicity of sizes is created than there is any necessity for. In comparison with the Swiss system we have within the same range six sizes to their five, their sizes being regulated by the diameter of the dials in French hues, but even this division we hold to be somewhat smaller than it might be. It would quite suffice if the difference were established as the tenth of an inch in the diameter of the dials between each size, the diameter of the top and pillar plates, and all the other parts of the movement, being proportioned thereto by a gauge divided to the tenth and hundredth part of an imperial inch. This division would give us five sizes of watch movement instead of seven, now commonly made. Fixed diameters should also be determined for the balances, wheels, barrel, &e., and every flat movement of the same size should have the same height of pillar with its plates of the same thickness and hollows вппк the same depth, which will enable the manufacture to get the wheels, etc., pivoted to the gauges, thereby creating another important division in the work The calliper of every movement of the same size should also bo the same size throughout, and all sizes should be of a calliper similarly proportioned to the fixed diameter of their dials. The exact radins

By Boethwick Smith, in Horological Journal.

of every wheel, barrel, and staff hole, also the j>~. tion of every screw, stud, dial-foot. etc.. and the mit line of every bar and cock should be «lefiued, whirs would, if generally adopted, admit of every sepam,port of tho complete watch being a 11 яЛфчмяЛ* finished article, including balances, с neun, dials caps, and all other parts that have now to be mad and fitted specially to each movement. It newi scarcely be asked whether the general adafticai l.r the trade of such a system would not at ox«* and thsame time make the trade less fluctuating, preuiot a more complete division of the Labour, cbenpeti tbcost of production, yet enable the workman to io crease his earnings, produce greater uniformity ir the style and finish of the work, and expedite tfci manufacturing process very considerably.

Having now at some length set forth what wt consider should be done, it may be required that »> should indicate the means whereby the general adop tion of such a system might be brought about, auj the details fully considered and determined opon

The first step to be taken would be to fix upon the measure which shall determine the scale of Eizm. the choice of which lies between—firstly, the Frencfc metre, or miffimetre, two of which are equivai :¡ to 078 of an inch, nearly; secondly, the French line. equivalent to -089 of an inch, nearly; and thirdly, tht 10th of an inch, to which latter ineosuremeut we have given the preference because it is English, and therefore aproper standard for the measurement of Englitt watchwork. This gives a dial 15 or Hin. in diameter, being proportionate for a full 8-size movement; th* next size with dial l-Sin. in diameter, the movemai: proportionate to which would he équivalent to an 11-size movement; next size with dial l'7in in diameter, proportionate to 11-size movement: next size with dial ISin. in diameter, proportionatr to 17-size movement; next size, with dial 1Эш. m diameter, proportionate to 20-size movement ; which, within the range from eight to twenty, gives five sizes of movement, in place of the seven sizes usually made and expressed as 8, 10, 12, 14, 16,18, and 20 sizes respectively, bnt 8, 10, 12, &c, what, no one can tell. For larger or smaller sizes the same scale would be maintained : and thai the difference in size that would be esUblisheJ by the universal adoption of this scale of measurement would suffice for all requirements of the tnde, may be adduced from the fact that Messrs. John Ryley & Co., of Coventry, have for the last three years successfully put the system ui practice, having had all their movements made to piit«t giving the calliper exactly proportioned throughout to the sizes of dials indicated above, and thai ixçfcrience nas. proved it of immense advantage in reducing the manufacturing process to an easy working system, and ensuring unif onnity not attainable by any other means, the system being adopted not only for the improved full-plate movements, but also for all the patent 4-plate centre-seconds and ¡plate movements made and finished by them.


MEDICAL and other students are at this time of the year purchasing a microscope will which to begin the investigation of animal ani vegetable structures. Others who would wish to invest in an instrument are detened by the expense on the one hand and by the fear of obtaining a worthless tiling on the other. Too strong a protest cannot be made against the notions prevalent with regard to microscopes, and encouraged by most the makers in this country. The handsome-lookinc instrument of great size, with its long tube anil innumerable wheels, is not to be recommended to the would-be observer, even should he feel jnstinea in the expenditure. The microscopes which are used in most of the German laboratories, where so mnch thorough work is done (to the writer's knowledge in Prof. Strieker's and Prof. RcJdtanrtT8 laboratories at Vienna, in Prof. Schweigeer Seidd s at Leipzig, and in Prof. Claude Bernard's at Pansi. are the little instruments of Hartnadt. which <K> not stand above loin, high, with a srmrde but buR« stage without any movement, no raekwork to the tube, but a sliding motion and a fine adjustment The instrument is used in the vertical position ««' complete comfort, and when liquid is on the stage, this position being necessary, it is of considérame advantage to have a small microscope over wtocu one can easily bend the head. Large microscopes, with their complicated machinery, are made to snit the optician who sells them, and not for the convenience of the observer. Those, who wish to get > microscope should insist either on havingon" these small and handy instruments made, or order one from M. Verick or M. Hartnack in Paris. Sncl1 a body having been purchased at a very minim"'" of cost, a larger sum may be expended on the really essential part of the apparatus—namely, the lenses. And here it will he found of great advantage to have the tube of the ndcroscope not more than tluv« and a half or four inches in length, for then the objectives of the continental makers can be used with the greatest advantage, though, with proper care«»

* From A'rtííire.

to thi! ocular or eyepiece, they niny be used on our ordinary long-tubed awkward English microscope. It Ы almost incredible that the English makers of object-glasses continue to demand three, or even four, times the price for their lenses which foreign makers do for lenses in every respect as good. For two pounds an object-glass may bo obtained of M. Veriek or Ы. Hartnack, of Paris, No. 8, which ia quite as good u glass and in some respects more pleasant to use than the one-eighth, for which üngliah opticinns demand eight guineas. Many persons anxious to work with the microscope ore deterred by the price of really first-rate instruments in this country. What we urge upon them most earnestly is to purchase such a body with eye-piece as that described above—simple but strong and steady—for between two and three pounds, and to equip the instrument with the objectives of MM. Veriek or Hartnack, say No. 2, No. 5, and No. H, which can bj obtained for another four pounds. We shall huve occasion again to speak of the merits of English and foreign objectives, especially of the immersion object-glasses. 4At présent we speak from personal experience, and desire to point out the convenience and cheapness of the small lnicroïieupe-body, and the thorough excellence and immensely diminished cost of the French makers' object-glasses.

L'uttioy Sections of Tissue*.—The method of "embedding," first practieedby Strieker and Klebs, is now extensively used in Germany, and is of very great assistance to the practical nistologist. It consists simply in surrounding the object from which sections are desired, with cither paraffin, »teorine, or a mixture of wax and oil. This latter is preferred at Vienna by Prof. Strieker and Dr. Klein, his assistant, and can be obtained of the exact consistency which may ba desired; usually parts are to be used. Á. little truy of paper is made, and some of the wax composition in a melted state is poured in. The object to be cut is then placed in the tray, and mare composition added, till the object is thoroughly enclosed. When hard, sections of the mass can be cut, the advantage being, in the case of thin lamina: or processes, that a complete support is offered by the surrounding composition, and a uniformly thin cutting may be obtained. For some purposes the microtome of Dr. Ranvier, of Paris, is very useful ; it is similar to one recently brought out by Mr. Stirling, of the Anatomical Museum, Edinburgh. In this little instrument we have a flat piece of brass with a hole in the centre, leading into a cylindrical chamber, at the bottom of which a screw works. A piece of elder-pith is excavated, so as to hold the tissue to bo cut; and when this has been well fixed in it, the pith is squeezed into the cylindrical box through the hole in the brass plate. A razor drawn along the surface of the brass plate cuts through the pith and the tissue it embraces, leaving a surface perfectly smooth and continuous with that of the plate. A turn of the screw, which works into the cylindrical box, now causes a certain very small thickness of the pith and tissue to project above the plate, and the razor again drawn across and pressed on to the surface of the brass plate, cuts a fine section, the exact thickness of wliich may be nicely regulated by the screw which pushes up the pith. This little instrument may be obtained at a small cost from M. Veriek, 2, Rue de la Parehamhmerie, Rue St. Jac

pies, Paris. It is not unlike an instrument described in English books on the microscope for cutting sections of wood, but its application with the use of pith, previously much in use for making sandwiches with delicate tissues which had to be cut, increases its value greatly. As to knives to be used in making sections, though some largo knives are made on purpose, there is nothing better than а first-rate broal-bladed razor. Dr. Moynert has cut his immense collection of brain preparations with a common razor.

Staining and Mounting TUsms.—The method which is now very extensively used ill German histological laboratories for the study and preservation of all kinds of delicate tissues, such as sections of the developing hen's egg morbid growths, fine injections, nerve tissues, &c, is as follows :—The section, either from a fresh specimen or from one preserved in alcohol, is placed in a solution of carmine in ammonia, from which all excess of ammonia

has been allowed to evaporate, as tested by the smell. The solution is also carefully filtered before use, and diluted to a small extent. After from three to ten minutes or more in the carmine solution, the section is placed in distilled water and thoroughly washed for some time by blowing into the water with a small pipette. From this the eection is removed momentarily to a watchglass containing distilled water and two drops of acetic acid, and then is placed in absolute alcohol. The water is thus removed, anil in five or ten minutes the section may be placed in oil of cloves, which renders it very transparent. From this it is removed to the glass slip, and is mounted in a solution of gum damara in turpentine, such as is sold by artists' colourmen. At any stage in this process we can proceed back again by the same steps, ammonia being used in place of acetic acid, and re-stain, rewash, or re-acidify as the case may be. If the staining is carefully managed and the subsequent

washing a thorongh one, most cellular structures are very beautifully and clearly brought out. Where rapidity is desired, and for the purpose of inspecting a specimen, it may be simply mounted in glycerine after the staining. The process above described is that of Gerlach and Stieda, and is preferred to any other by some observers of great experience. Thus Dr. Meyuert, of the lunatic asylum at Vienna, who is throughout Germany regarded as the great authority on the histology of the brain, uses this method for mounting his sections of cerebrum, cerebellum, ifcc. It is very convenient to have little glass dishes with covers for each of the above-mentioned re-agents, so that the sections may be passed from one to the other and left covered up, if desired, for a day or two—the waste of re-agents involved in filling watch-glasses each time they are required being also avoided. If preparations have been preserved in chromic acid, they must be very well washed before staining, and very often cannot be made to stain well at all. Various methods are useful in varions cases, but, as one of great general use, the carmine staining and oil of cloves clearing miiy be strongly recommended. Staining tissues with nitrate of silver, chloride of gold, and with bile-pigment are most important aids to the histologist. the merits of which have been recently much discussed, and of which we shall have a word to say from experience.

Glycerine Jelly.—This composition, which has been lately introduced, melts at a lower temperature than Deaue's medium, and has a greater clearing action on the objects mounted in it. A small piece of the jelly put on a glass slip and warmed, soon liqúenes, and is ready to receive any object, after which the cover is directly applied. For objects which do not require any great amount of "clearing," it is a most useful medium. Insects, worms, small crustácea, &c, may be mounted in this way excellently.

E. Ray Linkester.



Hon. SecWilliam F. Denning, Ashley-road, Bristol.

Report of obtervatMns made by ttie member* during the

period from May 7 to July G, 1870, inclusive.

SOLAR PHENOMENA.—Mr. John Birmingham, of Tuam, writes :—" A remarkable obscuration of the sun was observed here on May 22. It lasted from sunrise to sunset, with a short interval in the afternoon of returning brightness. The sun was of a beautiful pink colour, though there wa3 no fog whatever, and its light was so reduced as to permit a long observation of it through the telescope, without the aid of a dark glass. I am informed that the same phenomenon was noticed in the South of England on the next day (the Sftrd), and on that day also, but late in the afternoon, it was observed at Rohrbach (Moselle), and described by M. Hainat m a letter to the Scientific Association; so that the cause of the obscuration, whatever it was, seems to have been moving eastward and southward." Mr. T. W. Backhouse, of Sunderland, reports that in May "there was a remarkable case of a Holar spot making a revolution round another. It occurred with respect to the two largest spots of a group that was half away across the northern zone, on May 9. The smaller spot was south of the larger, on the 7th, at 8h.„ but preceded it on the 12th, at 21h., the line joining the two spots having rotated through an angle of 80° or 90' in 5? days. This movement continued to the 15th, but this wonld be partly apparent, owing to the group approaching the limb. By that time the larger spot was reduced to the size of the other. I cannot say whether the motion was a curved or a straight line, though it was probably the former; nor can I say which of the spots moved, or whether both did. They were about 22,000 miles apart on the 9th, at 3h., but on the 13th, at 20h„ they were 32,000 miles apart. One spot must therefore have moved, relatively to the other, about 34,000 miles, in Ц davs, or at the rate of 300 miles per hour." "Mr. T. G. É. Elgar, of Bedford, says :—" The sun spots observed during Juue were, with the exception of one group, small and devoid of interest when compared with those soen in April and May. The largest spots were confined to the sun's northern hemisphere. Between the 8th and 15th the spots were all small; on the latter date there were only two groups on the disc, and these were insig»ineaut. On the 19th a very remarkable spot was observed, it formed the preceding member of a large scattered group 2' 62' in length; its penumbra measured about 1' 10" in greatest diameter. At 10 a.m., an isolated mass of light, intensely bright, was remarked on the nucleus; this at 2 p.m. formed a "bridge" connecting adjacent sides of the umbra. The nucleus of this spot was very uneven in colour. At 5h. 15m. p.m., on the 19th, the enitral portion was noted as brown and the border a* black, and on subsequent dates the variety of tint was still more marked. At 7 a.m., on tho 21st., when the penumbra showed evident signs of cyclonic action, not more than half the area of the nucleus was black, the remaiuder was made up of patches of various shades of brown. The group disappeared at tho limb on the 27th." The Rev. S. J. Johnson, of Crediton, observed numerous spots on the sun on May 13th. There were then four groups with penumbrie close together. W. H. Michel Whitley, of Penarth, says :—" June 21, I noted

on the sun's disc one very large, round, and wcll<1 e fined spot; on one sido, however, tho penumbra was invaded by two tongues of faenho for a short distance, and in the centre of the umbra wax a bright patch."

The Planet Saturn.—Mr. H. Michell Whitley repeatedly observed this object with hi i (Hin. reflector. He says:—"June 21.—Air very unsteady, but after midnight better.—The Bill : Duller yellow than rings; equatorial zone yellow; north of thi'; a pale red belt, and anothor further north again towards pole, much fainter, and about midway. Polo of planet bluish grey, edge a of ball slightly shaded; no other spots or markings.—Ring A: Inferior in brightness to B; colour pale yellow i no subdivisions or markings on it.—JiaW* division: Traced all round; widest and darkest, if at all, in W. Ansa; sharply defiucd in was not so black as the sky, bnt deepor than the crape ring across the ball; colour dusky.—Ring Б; This ring was very bright for a short distance from its outer edge, which was very sharply denned; colour gradually deepens and light fades towards inner edge; outer edge lemon yellow ; duller and deeper inwards; strongly suspected to be shaded, but no actual subdivision scon. No line of light on innor edge of ring wliich was not sharply defined.—Ring С or crape ring; Very delicate colour, dusky purple; I could with care, as u very line object, trace the edge of the globe through it up to ring В., equally distinct in E. and W. Ansa. No markings of any kind upon it. June 28.—10b. to llh. 15m., power 250, definition very fluttering. North equatorial ruddy belt very distinct. Equatorial yellow band the brightest part of the planet. Between tho north equatorial ruddy belt and north pole, lay one or more very faint ruddy bands. Pole: pale bluish grey. No other markings. Tho crape ring very dark and distinctjacroes the-ball. July 2.—10b.¿definition very sharp, power 250, a glimpse observation. The two belts before mentioned very much plainer and darker than on June 21, Í8, and not of such a ruddy hue.''

Lcnab Observations.—Mr. John Birmingham, of Tuam, Ireland, reports that on June Cth he saw " a very marked central depression in the white Bpot of Linni', though the Terminator was so far away as the boundary between tho Marc and the Palus Pntridinns. The depression wa* rather east of the exact centre of the white spot, so that the western exterior elor*e was longor than the eaatexn." Mr. H. Michell Whitley has observed, with great care, manv interesting and difficult lunar objects, and the results of his observations Lave been sent to Mr. W. R. Birt, F.R.A.S.

Winnecke's Сонет.—Mr. Gecrgo J. Walker, of Teignmoutb, observed this body on June 6th, 6th, and 7th, and he says that " it looked like a tolerably bright nebula." On tho 6th, at 14h. 18m., the comet looked faint, owing to the strong twilight.

Meteors.—Mr. G. J. Walker saw a splendid meteor on June 24th. It traversed the greater part of the sky, and was much larger and brighter than Venus. It was of a blue colour. Mr. Walker adds, "I think it appeared a little to the right of Altair, and passed uear Vega, and on^t ) the Pointers in Ursa Major; it had a magnificent train, and, I think, must have traversed an arc of about 120°. The time oi its appearance, as well as I could make out from my watch, was llh. 18m. Greenwich mean time, and it may have been 7 or 8 seconds making its sweep over the heavens. I did not hear any sound with it." Mr. H. M. Whitley observed a brillinnt meteor on June 29th, at llh.30m. It was of tho second magnitude—"pale yellow, velocity very great."

A New Red Star.— Mr. John Birmingham ha* "frequently observed a red star in Cygnns, not, I believe, previously noticed; at least it is not in "Kehjííllernp's Catalogne" (Ast. Nach., No. 1591 /, which gives a list of all the red stars known up to 1806. It is of a deep red, of about the eighth magnitude, and is near a blue star of the same size. Its approximate position, compared with 32 Cygni, is about K. Ä. 'JOh. 15m. 37s. Declin. + 47° 27' 28"."

Occultation.—Mr.Walker witnessed the occultation of 0 Libra on June 11th, and found that the exact time of disappearance was 9h. 27ra. 55-tis. Greenwich mean time.

EXPORTS OF MACHINERY.—Dnring the first four months of the present year the value of the steamengines and machinery exported from the United Kingdom showed a sensible Improvement as compared with the corresponding period of 1839. Steam-cut'mes were exported, to April 30th this yenr, to the value ef £575,041, as compared with £409,492 in the flrbt four months of 1869, and £431,472 to the corresponding date of 1868. The increase observable this year was chiefly attributable to the greater demand for eteam-engiues from Egypt, which took them to the value of £106,424 in the first four months of this year, against £29,054 m 1869, and £18,259 in 1868. General machinery was exported to April 30th this year to tho value of £957,670, as compared with £848,934 in the corresponding period of 1869, and £725,960 in 1868. There was an increase this year in the exports to Franco, Spain, Egypt, and Australia; and a decrease to Russia, tho Hanse Towns, Holland, Belgium, and British India.

AN ATMOSPHERIC TELEGRAPH.—A novel kind of telegraph, the invention of Signor Guattari, an Italian, was submitted to the inspection of A party of scientific gontlemen on Monday week, at a private house In Gloucester-et-, Warwick-sq. The inventor aims at obtaining by the use of atmospheric power tho same or better results than those attained by electric and magnetic forces To this end he charges a reservoir with compressed nir and, by the operation of valves worked in the samo manner as those in use in the ordinary telegraph system, sends pulsations through a tube, which pulsations are made to work upon the receiving instrument with an effect corresponding with that of the electric oarrunt' passed along insulated wires.

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