When we contemplate the benefits of the natural world, we do not often realize what a wonderful object is the sun, and how manifold are the kindly offices it constantly performs for us. From an inconceivable distance in space truly it rules the earth, imparting to it light, heat, and other subtile influences, and rendering it a possible abode for countless forms of life. The ancients were right in placing it foremost among the grand objects of creation, and we can hardly wonder that it was eafly chosen by idolatrous nations as an object of worship. Of its size and distance the first astronomers had no true conception. Anaxagoras, who lived 430 years before Christ, claimed that it was as large as the whole territory of Greece, for which he was heartily laughed at. In later times, Leonard Digges, a quaint English philosopher of the sixteenth century, estimated its distance at 64,811-J miles, which is, in reality, barely a fourth of the distance to the moon! At the present day we smile at such guesses, knowing that the Grecian peninsula would, if laid on the sun, be absolutely invisible when looked at through our largest telescopes, and that, as regards the distance of the great orb of day, our friend Digges does not give us a thousandth part of the truth. If we attempt to obtain a conception of the vast magnitude of the sun, we find ourselves thoroughly bewildered. Were we at its center, our moon would revolve in its orbit but little more than half way to the sun's surface. If it were a hollow sphere, there would be sufficient room to accommodate more than 1,200,000 balls the size of our planet. The earth is a mere homeopathic pill in comparison with such a body; and if proj ected on its bright disk, would, from our orbit, be absolutely invisible to the naked eye. Illustrations like these do little more than show that by no effort of the imagination can we obtain a satisfactory idea of the gigantic proportions of the nearest fixed star—our sun. When viewed with a small telescope, care being taken to shield the eye with dark-colored glass, dusky spots are often detected on the solar disk. At the present time they may be seen with the veriest toy spy-glasses, and I have frequently so seen them when, without such modest assistance, they CDuld not be detected. As the next two or three years will be rich in sun-spots, our young readers will have ample time to try their hands in this department of astronomical science. Either a spyglass, or opera-glass, will answer; and if colored glass is not at hand, an ordinary piece, smoked in a candle flame, will do very well. You must not, however, give up the search, if at first unsuccessful, for the curious blotches are constantly coming and going, and sometimes appear quite suddenly on the disk. They pass slowly across from the eastern to the western side in about fourteen days, not, however, owing to their own motion, but because of the sun's rotation. Should a group continue in existence so long, it would reappear on the eastern edge after the lapse of another two weeks, but this does not often happen. It is by means of observations of this kind, made through a long series of years, that the time of revolution of the sun upon its axis has been ascertained as twenty-seven and a quarter of our days. Astronomers describe sun-spots as consisting of three distinct parts; the penumbra, or " almost-shadow," the umbra, and the nucleus. The penumbra consists of a grayish appearance, not unlike a dark cloud, which encircles the black center, like the fringe to a mat. It is the most conspicous portion of the phenomenon, and from its varying character possesses the chief interest. It is most frequently made up of long, thin wisps of cloudy matter, extending inward to the center of the Spot. The nucleus is but a darker part of the already deep brown, or black umbra. It is only seen under favorable circumstances; as when the telescope is a large one, and in good working order, the atmosphere clear and still, and the observer's vision acute. One of the most interesting features of the sun's surface is the delicate mottling which may at almost any time be detected, if the atmosphere is moderately free from vibrations, and the telescope a good one. To see it satisfactorily, an instrument, in which the principal lens measures two or three inches across, is necessary. We may compare this mottling to the appearance of tissue paper held up to the light; or better still, to the tufted surface of light gray chinchilla cloth, such as is used for heavy winter overcoats. But best of all, we may liken it to the snow-white ends of coral branches. The mottling of the sun would seem to vary considerably in appearance from time to time; sometimes resembling a sky covered with mackerel clouds, and then again presenting the compact and well-defined arrangement of the coral tips. Let us consider for a moment what happens in the case of the union of the little black points alluded to. The bright envelope called the plwtospliere—which is what we see when we look at the sun—is evidently pierced in some unaccountable manner; and the rent growing larger and larger, a deep cavity in the luminous covering ensues, and the penumbra is formed. Should the cause of the phenomenon prove sufficiently violent, the true body of the sun is then seen through rifts in the cloudy strata. But instead of being- white—daz-zlingly so we should expect to find it—it has a dark brown tint. This is, however, an effect of contrast, just as coal fires look dull in sunlight, and the calcium light positively black, if placed between our eyes and the sun. The central mass supplies the materials for the illumination, but is not as bright as the dazzling light it produces, any more than in the case of a candle, the intensely hot and luminous gases enveloping the glowing wick, give out light equal to the upper portion of the flame, where combustion is perfect. Thus a sun-spot is by some considered as a tearing aside of the long flames issuing from the liquid or gaseous sea beneath, revealing the less brilliant lower strata of flame (to our view the penumbra), and the still less luminous body of the sun itself, the latter appearing as the umbra, with or without a nucleus, as the case may be. The materials of our sun are, doubtless, capable of producing greater heat, pound for pound, than the substances usually employed by us for the same purpose. Eecent researches in chemistry would seem to point to a more elementary condition of matter in the stars and nebulae, than any with which we are acquainted on the earth. Who can say but that the production of our terrestrial elements was accompanied by displays of light and heat similar in intensity to those now witnessed in the sun and stars. This theory has great support in the constantly accumulating facts which the spectroscope is bringing to our attention. One of the most impressive sights which ever falls to the lot of man to witness, is that of a total eclipse of the sun. Such an event is comparatively rare for any one part of the earth's surface, so that one may live to a good old age, and die without having witnessed such a phenomenon. In London, for instance, there has been no total eclipse since the year 1715; and more than five and a half centuries had then elapsed since the previous one. The characteristic features of such an occurrence are the following : The peculiar gloran which spreads itself, like a pall, over the landscape; the changing tints of the sky, black, orange, indigo, red, sickly yellow, and leaden hues appearing at one and the same time, in different portions of tbe heavens; the awful approach of the moon's shadow in the air; and lastly, the magnificent circle of light around the eclipsed sun, called the corona, which is compared to the " glory" around the head of a saint, in an old painting. We might add to these the rosy flames frequently seen issuing from the dark limb of the moon, but in reality connected with the solar atmosphere. These flames are often to be seen with the naked eye. During the past year they have been analyzed by the spectroscope, and found to be masses of self-luminous hydrogen. Finally, the larger planets, and some of the principal stars, are occasionally recognized by acute observers during the period of totality, as the gloomiest part of the eclipse is called.— W. 8. Oilman, Jr., in the Riverside Magazine. Purifying; Water. It is a well-known and generally observed fact that the water of rivers, canals, and some lakes is never quite clear. This turbidity, which often remains even after many days of quiet rest, is partly due to inorganic substances floating about in the water and suspended therein, but is far more frequently caused by matters of an organic nature too minutely divided and too small to be readily recognized, even by a powerful microscope. The researches of some of the. members of this report have undeniably proved that, at least as far as the N etherland waters they submitted to research are concerned, this turbidity is due to extremely minutely divided clay, by the aid of which a great deal more of organic matter than could otherwise remain suspended is kept in such an extreme state of division as to pass through filters and not deposit, even after many days of rest. When, to such kinds of water, a solution of alum (from l-50,000th to l-100,000th of the bulk of the water) is added, it will be observed that after a longer or shorter lapse of time a flocculent precipitate is formed, which is either alumina or a basic sulphate thereof, which flocculent material takes up all the turbidity of the water, leaving that perfectly clear; the precipitate thus formed has been submitted to chemical tests, and it was found to contain a large quantity of organic matter, and to yield, on being heated with soda-lime, ammonia very largely. Since the committee was instructed to ascertain and discover the means of improving the condition of the potable waters where it was required, this especially also applied to the towns and villages whose chief supply of water for domestic and drinking purposes depends upon that of the river Maas, along the banks of which, in the lower portion of its seaward course, the population is entirely dependent upon its water; which has been almost from time immemorial known to produce, in those not accustomed to its daily use, a diar- rhea, which in certain individuals is accompanied by very unpleasant, if not always, therefore, dangerous symptoms. The water of this river has been analyzed over and over again by many eminent scientific chemists, and has been submitted to microscopic research, but no trouble, nor anything science could, armed with its best weapons, bring to bear on this research, has ever revealed the precise cause of this peculiar property, which is not possessed by the water of the same river, nor also by that of the Rhine, higher up its course. For curiosity's sake, we here quote the result of one of the most recent analyses of this water taken at flood tide at Rotterdam : Physical properties, very turbid, does not become clear on standing, is not rendered clear on addition of a few drops of hydrochloric acid; taste—not quite unpalatable; solid residue—dried at 120 C, yielded, for 1 liter, 0195 grm., containing 0055 of combustible matter; earthy salts- 0-0975 grm., containing 0-048 sulphate of lime, chlorides of alkalies, 0-0233; ammonia, none; slight tracs of nitrates; dry residue had a yellow color before ignition. It is a highly important fact, and one of very general importance to learn, that Dr. J. W. Gunning, of Amsterdam, has found that the perchloride of iron added to this water (and the same applies to far more foul waters experimented upon) has the effect of rendering it perfectly wholesome and even agreeable for use. To one liter of water, 0-032 grm. of the dry salt just alluded to, and previously dissolved in pure water, are added, and, after well stirring the liquid, it is lerc quietly standing, to settle, for full thirty-six hours. * A series of very carefully made experiments has proved that no free hydrochloric acid (the quality thereof contained in the above-stated weight of perchloride of iron only amounts to 0'021 grm.) was left in the clarified and purified water, but in order to suit the application on );he large scale, and to make assurance doubly sure, as regards any acid or perchloride being left undecomposed, or rather uncombined, with the organic and inorganic matter of the water, Dr. Gunning has advised that a small, but equivalent, quantity of crystallized carbonate of soda should be also added some hours previous to beginning to take the purified water for use. At Dr. Gunning's request, a scientific gentleman of high attainments, who happens to hare an excellent opportunity, near Rotterdam, to try on the large scale this process, has submitted it to practical test, arid a quantity of np less than about 240,000 liters of Maas water, taken at all times of the year, has been treated by this process, and thereby rendered perfectly fit for use, and consumed by various parties, has proved to have been entirely deprived of its property of causing diarrhea; moreover, the medical officer in charge of the crew of Her Majesty's corvette the Lynx, moored off Rotterdam, in the river, has applied this process to the water taken from the river, and found by experience that the thus purified water has even the good effect of restoring to health such of the ciew as had been incautiously drinking the not previously purified Maas water. It is, wlien using this means of purifying bad water, of great impor: ance to let the sediment quietly settle; it occupies about 4 per cent of the bulk of the water, which on the large scale will, for security's sake, be submitted to a filtration through fine well-cleansed sea-sand before being sent through the mains of the large waterworks intended to be established near Rotterdam for the supply of that town. The quantity of crystallized carbonate of soda which is equivalent to 0032 grm. of dry perchloride of iron is 0085 grm.; both these quantities are the maximum required to render the Maas water perfectly pure, even at the time when it is most turbid; comparative experiments have conclusively proved that the application of this process is very superior to filtration of the water, even through animal charcoal. The result obtained with the Maas water having been so eminently successful, the committee has applied this method to the purifying of water otherwise non-drinkable, such as is met with in many of the smaller canals, brooks, and also pumps yielding surface water of bad quality in many parts of the kingdom, and the results obtained are such as to justify the order that this method of purifying must be applied by authority to a class of waters which, thus treated, become available for use. The precipitate formed by the addition of the perchloride of iron and carbonate of soda, both previously dissolved, has been proved, by accurate analysis, to contain a large quantity of organic matter, which, on being ignited with soda-lime, yielded ammonia very largely; analysis has also proved that, as regards the Maas water, the only addition to its inorganic constituents is that of one part of chloride of sodium, by weight, in 40,000 parts of water by the application of this process. Dr. Gunning has found that the effect of the perchloride is not so conspicuous with some well waters containing much carbolic acid; while, moreover, there may exist in some of these kinds of waters, either in quantity or quality, inorganic salts which delay or altogether impede the peculiar mode of flocculent precipitation observed with the aboved-named Maas and other waters to take place after addition of the iron salt.—Chemical News. Forms of Saw-Teeth. The rules for regulating the forms of saw-teeth must necessarily be arbitrary, as much depends upon the nature and quality of the wood, and the direction in which it has to be sawn. In cross-cutting, the object is to sever every fiber or thread, and as the material in this direction is almost non-elastic or unyielding, teeth of an acute and nearly lancet-shape must be employed, so that acting like a series of knives in rapid motion, they cut the threads asunder rapidly and sweetly, the saw-dust produced having a fine granular appearance. On the other hand, in ripping or cutting with the grain, the desideratum is to separate the texture, as it were tad as in so doing the teeth do not meet with so much re" Sistance and resilience from the filaments as in cross-cutting' they may be made much larger and coarser, thereby pro" ducing small shavings or chips, rather than saw-dust. The nature and quality of the material to be sawn has considerable bearing on the configuration of the teeth/which, following the general law of cutting tools, and agreeably to common usage, have to be more obtuse or acute according to the disposition of the substances opposed to them. Soft and pliable woods, such as pines, willow, alder, limes, etc., require the use of large teeth with acute points and considerable pitch, whereas hard woods, or those of a tougher and denser consistency, as oak, mahogany, rosewood, etc., necessitate the adoption of teeth of perpendicular pitch and diminished space. Yellow deal, pitch pine, larch, etc., are of so gummy and resinous a character, that the teeth require not only more set but the blades themselves have to be smeared with grease, to keep them cool and decrease the friction arising from the adherence of the resin during motion. Similar results are experienced in working soft woods; the teeth become choked by the damp consolidated saw-dust, and obstinately refuse to perform their duty without extra force.— Worssam on Mechcm-ical Saws.