Volume 17 (1868) (428 pages)

The Mining and Scientific Press. 3 Mechanical, The Durability of Materials, _A very interesting paper was read by Mr. Edwin Clarke before a late meeting of tho . London Institution of Civil Engineers, on) ‘Durability of Materials,” from which we eondenso as follows; ‘Tho list of materials . used hy the Engineer is small, Itinelndes . stone and timber among uatural produetions, and hricks an:] eement and the metals among artificial prodnets, Itis diflieult to state, oven approxiniately, the positive life of either of these articles. The durability of any material depends, not merely on its own inherent properties, but principally on the agencies to which it is exposed ; as, for instauce, the effects duo to elimate. On examining all the facts and seeking gome eommon clinracteristic, it is found that among all the cunses of deeay, humidity holds the first rank. The decaying influence of humidity was evidently dependent on other coineident circumstances. Tho mere pressure of water, or even of p saturuted atmosphere, is not sufficient to indnee rapid decay, which appears to be eaused by humidity only under peculiar conditions. Ono of these conditions is well known by the popnlar title of dampness. Tho decay caused by dampness, as in the ease of dryrot, is effeetnally prevented by the presence of water or by a constant enrrent of air, whether perfeetly dry, or saturated to any degree of hnmidity. Dampness, therefore, is uot the mere presenee of moisture in the ordinary formin whiel it is held in solution by theatmosphere. If an hygrometer’were placed in a damp situation it would simply indicate perfeet saturation ; no ovaporation wonld take plaee, but the eottou eovering of the wet bulb will be speedily covered by a peculiar mould, well known by its fanguslike odor, and iu a short time it will he converted into an impalpable powder, or ash, Under similar circumstances timher, leather, paper, and all like materials underfo the same rapid decomposition; vegetxble gums and oils, that are insoluble in water, and even dry hard paints and yarnish, becomo soluble and liquid. Massive timhers are rapidly disintegrated, entirely losing their weight, though still retaining their form ; and they are often totally free from apparent moisture, altbough at times dotted externally by drops of brilliant water. Damp spots are, moreover, peeuliarly hygrometic, indicating atmospheric changes with remarkable precision, and temporary desiccation in no way disturbs this precess. The peculiar odor which always accompanies this eondition is one of the best tests of its existence; and the ex_ pression that a room smells damp is strictly correet. Theeffect is, within certain limits, intensified by increase of temperature and absenee of light, and arrested hy poisons destruetivo to vegetable life. If this phenomenou of deeay is more elosely examined the process would be found to resemble, in many respects, a slow combustion. The ultimate results of combustion and .deeay are strikingly similar ; the union with oxygen is slowly effeeted, and the residue is more or less diluted with foreign substances ; but whether bodies are burned or deeayed the remains, in thoashes, are substantially identical. Deeay may thus, to a great extent, be looked upon as a decomposition, resulting from the slow chemieal combination of oxygen witb the matters deeomposed. Now, if slow combustion is the eause of decay, and that particular state called dampness is so important an aecessory, tho inquiry naturally suggests itself: What connection exists betweeu those agencies, or in what way eau damp promote the absorption of oxygen? In tho case of organic substances, the presence of vegetation in the form of fungns, or mold, is an invariable characteristic of decay, and the decomposing effect of all vegetable growth is beyond question. It may be said, that the vegetable growth alluded to is the effect rather thau the cause of deeay. Doubtless, the spores of microseopic fungi followed the law of all other seeds in vegetating only under the peculiar Conditions of soil, light, and moisture which were adapted to their growth ; dampness and partial darkness, and absolute quietude, and even deeay, may bo essential to their existenee ; and, therefore, itis only under such conditions that they appear at all. But, nevertheless, when they do appear, their preseneo rapidly aecelerates deeay, and they furnish a vital medium, capable of accomplishing tho observed effeet—eombustion, or slow union with oxygen, of the substauees on which they thrive. It is probably by some sueh chemical vital action that tho faet can be explained, why even tho hardest roeks aro rapidly dosomposed by the growth of lichens, or that deeay should be arrested by poisons whieh econld exert no other infiuenco than the prevention of vegetation. It was equally remarkable that in the putrefactiou, or rapid ehemien] decomposition of animal und vegetable substances the same profusion of tho lower forms of animal, us well as vegetable, organisms eharacterize the phenomenon, Whatever may he the enuso of deeny, moisture is an indispensablo element, Dry air is inenpablo of deeomposition. Water ;isa earrier of oxygen iu a potent form ; and it was only from water, aud more espeeially when iu tho form of vapor, that the oxygen necessary for decay ean be obtained. The durability of tin and iron roofs in Geneva and St. Potersburg is dne to the absenec of moisture ; and the importance of some shelter for timber, and of thorough ventilation, wherever it is employed in a moist elimate, is a neeesssry eorollary. We shall next week eontiuuo our notes on that portion of the paper of Mr. Clarke, wherein he speaks of the durability of nretals, Magnet Test of Iron---the other Side. _ Mr. Jolin Farquharson, of Her Majesty’s Dock-yard, Sheerness, sends a paper to Engineering, ix which he takes a different view of tho above-named subjeet from that advaneed by Mr. Saxby, of whose eonelusions we gave asumming-up two week since. It will bo rememhered that oue of these conclusions was, that free magnetism was not confined to the surface of a body, but distributed thronghout the mass, Mr. Farquharson, after refuting certain other positious by Mr. Saxby, takes up this one, and closes his paper with the following remarks upon it: “The amount of free magnetism in iron is not direetly as the mass, nor exactly as tho surfaee, although nearly so. Barlow found that a sbell 10 in. in diameter and 1-36 in. thick, had two-thirds the magnetism of a solid sphere of that diamcter; and aceording to Poisson’s formule, a cylinder 10 ft. diameter and 474 iu. thiek has as much free magnetism as a solid cylinder of that diameter; but it has been objected that this is only true when the continuity is regularly interrupted—a condition not to be anticipated in aetual practice, and I havo endeavored to test this experimentally with tho following result: A cylinder 4 in, long, Zin. diameter, and 4 in. thick had a cylinder of iron borings roughly fused together by molten iron inserted, and slowly revolved within the hollow cylinder; the needle was perfeetly steady and unaffected. The like resnlt followed the suhstitution of a solid and also the half of a solid cylinder of the same deseription of iron tor the rough cylinder of borings, the defleetion in either case remaining the same. It appears, therefore, that tho free, magnetism acting upon a needle is due to a stratum cf iron near the surface, and that considerable irregularity iu the internal structure of a bar of iron 2in. thick may exist without affecting the needle. But the praetice, so far as I have seen, is to use a very light noedle near the surface of the iron, and to disregard altogether the induetive influence of the needle. Now a cylinder of the thinnest iron that can bo produced will defleet a needleso used 90°; a solid mass can do no more, and I can see no reason why we should not find the same varieties between this and the ueutral point, where deflection is uil. We must, therefore, it appears to me, remain quite uneertain as to the condition of the internal mass at a greater distanco fromthe needle.” Puantne-Macuinr Breps.—Au idea has been advaneed that the beds of planing machines should he reversed onee a year where their construction pormits it. This will equalize the wear of the slides and make them truer than they wou!d otherwise be. Carclessuess will often in twelve months so injure 2 planiug machine that nothing willcure it but being made over. If, however, the artisan be up to his business, ho will so arraugo his work on the bed that it will wear true at all times; if he is obliged to work auy leugth of time on one end of the bed, le ought to divido the periods so as to run first one end of the platen over the slides and then change tho other end. In this way the best results will he obtained. Scelentifie Miscellany. "The Heating Power of the Moon. Myr. Harrison reeeutly read an interesting paper before tho British Royal Astronoimical Society on the capacity of tho moon to receive heat from the sun and to radiate the saine intespace. Assuming that the lunar surface hns a capucity for heat, equal tothe surfaee of tho earth, that luminary must, during its long lunar day, of uearly filteen of onr days and nights, storo up on any giveu snrfaee exposed to tho action of tho sun’s rays during that leugth of time, a very large amount of heat. he moon’s hemisphere, visible to ns, would Le heated to its greatest possible extent during tho third or last quarter, whon the half moou thus illuminated has been subjected to the eflects of solar radiation for a mean duration of about eleven days, and the remaining half, then in shade, has recently been receiving the sun’s rays for a period of equal duration. Hence, if the moon radiates heat as farinto space as to reach the earth, it would be at that time that our planet would be reeeiving its maximum of hoat from its satelite. Now the heat thus assumed to be acquired by the moon, and radiated into space, is dark heat; andas it is known that the aqueous vapor in the atmospbere has a power of absorbing dark heat, says Mr. Harrison, hence, the heat radiated by tho moon, instead of conveying warmth to the earth’s surfaee, is employed in heating the aqueous vapor in the atmosphere above the clouds. Tho clouds would thus be raised toa higher elevation, and of course to a greater or less extent dissipated. There would also be a sensible fall iu the temperature near the earth’s surface caused by such eyaporation or rarifieation, Myr. Harrison further stated in his paper that the daily mean temperature at the Oxford, Berliu aud Greenwich observatories, when reduced to tables, according to tho age of the moon, show that the temperature of the air near the surface of the earth is affected by the moon in the mauner aboye deseribed; and that the maximum mean temperature oceurs about the seveuth day of the lunation, and the minimum after the full moon, These results, if as stated, would be re‘markably confirmatory of Mr. Harrisou’s views, We may here remark that the editor of the London Quarterly Journal of Science, differs from Mr. H. ‘The editor holds that the moon does indeed exert a marked influence, but ot for the reasons assigned by Mr. Harrison; but because that influence is exerted (in consequence of the varied times at whieh the moon reaches ber meridian) at more or less favorable hours of the day—such hours as those in whieh the hygrometrieal state of the atmosphere, whieh varies at different hours of the day, is most favorable for the development of such phenomena, As respects the heating of the moon’s surface, tho Quarterly remarks that, although thero is undoubtedly an enormous quantity of heat poured upon a lunar hemisphere, in the courso of the long lunar day, yet we have.no means of knowing how that heat is disposed of. Nearly all of it may be radiated into space, or a large portion may be consumed in effeeting changes —as of solid into liquid, or of liquids into vapors—followed by a return to the original state during tho equally long night whieh follows. The Qzarterly thinks it bardly possible that the heat stored up in the moon during its day, beeomes sensible tous, by radiation, during its following night; but rather far more probable that the heat we aetually reeeive {rom the moon is from refleetion, procisely as we reeeive her light. Iv has been found that steel rifle-barrels when fired off several times in a northerly direction, aequire magnetic propertie +. Cotor Ix Astronxomtcan OBSERVATIONS. Mr, J. Browning, F. I. A. §., has published a paper in the Chemical News, in which ho shows quite eonelusively thatthe difference in tho apertures of different teleseopes affects materially tho appearance of the heavenly hodies to the observer. The eolor of a given star, or of the moon during au eclipse, ete., appears very different to tho observer wheu he ehanges his teloseopo from a four toa six or seven ineh aperture. From this it follows that the estiniate of eolors, in astronomieal observations, must bo coupled with the diameter of the aperture of the telescope through whicli the ohservations are made, For instance, the small star in the eluster Perseus, appears of an indigo-blue with an 8% ineh, Prussian-bluo with a 104 inch, and royal-blue with a 15'{ inch aperture. This diseovery accounts for some most singular discrepaneies notieed by observers, whieh have beretofore been attributed to color blindness, Curuustry or Writinc.—Writing ink, with trifling variations of proportious, is a compound of sulphate of iron, extraet of galls, and gnw, held in mechanical union by soft wator. When tho fluid is applied to the paper, the following ehemieal actiou oeeurs: The oxygen of the atmosphere forms gallic acid with the tannin of tho galls, whieh, iu turn, unites with the iron in solution, forming a black precipitate (the per-gallate of iron), and the sulphuric acid, thus set free, enters the body of the paper, while the water passes off by evaporation. When the presence of this sulphuricacid in tho tissue of the paper is in excess, the paper is gradually destroyed. It should be the aim to obtain an ink which will leave tho least acid in the tissuo, and still give a permanent black color. Expansipinity oF Bismure.—Bismuth is a metal which, unlike other metals, expands on fusing or cooling. Mr, A. Tribe recently read a paper before the London Chemical Society ‘‘on the Freoziug of Water and Bismuth,” in which the author made mention of a series of experiments whieh proved that, although bismuth, like water, increases in bulk on freezing; yet this increase is only at the moment of congelation. Thisis no evidence that, as is the case with water, any expansion tales place before solidification. Srrctra oF Merrzors.—Mr, Browuing has invented an ingenious contrivance for reducing the angular velocity of meteors so as to enable him to obtain their spectra. With this deviee he has found it easy to ohtain the spectra of balls shotfrom a Roman eandle—the characteristic lines of baryta, strontia, etc., can be readily distinguished in their spectra. : Buow-Prrer Braps,— Prof, G, Rose has studied some curious phenomena exhibited by eortain blow-pipe beads. He finds that tho opacity which they frequently assume on eooling, results from the separation of mieroscopic crystals. The Professor’s researches on the reaetion of titanic acid appear to have some bearing on the natural formation of anatase. Trunprr Mapr Visreue.—Dr. Topler foealizes a ray of light on the object-glass ot a telescope, whieh is conueeted with a screen in sueh a way that any disturbanee of the air becomes visible; foriustanee, the intense sonorous vibrations of the atmosphere produced by electric explosions show themselves in the teloseope as visible rings or cireles of light.Discovery 1n Maanntism.—M. Gerard has discovered a vory curious faet. If a metallie ring made of wire, the diameter of which varies regnlarly, so that at one side of the ring itis very thin and atthe other side relatively very thiek, be suspended over an . eleetro-maguet, it will begiu to revolve. The author sees in this fact the germs of a . new system of eleetric telegraphy, for the . details of whieh we wait.

The Mining and Scientific Press. 3 Mechanical, The Durability of Materials, _A very interesting paper was read by Mr. Edwin Clarke before a late meeting of tho . London Institution of Civil Engineers, on) ‘Durability of Materials,” from which we eondenso as follows; ‘Tho list of materials . used hy the Engineer is small, Itinelndes . stone and timber among uatural produetions, and hricks an:] eement and the metals among artificial prodnets, Itis diflieult to state, oven approxiniately, the positive life of either of these articles. The durability of any material depends, not merely on its own inherent properties, but principally on the agencies to which it is exposed ; as, for instauce, the effects duo to elimate. On examining all the facts and seeking gome eommon clinracteristic, it is found that among all the cunses of deeay, humidity holds the first rank. The decaying influence of humidity was evidently dependent on other coineident circumstances. Tho mere pressure of water, or even of p saturuted atmosphere, is not sufficient to indnee rapid decay, which appears to be eaused by humidity only under peculiar conditions. Ono of these conditions is well known by the popnlar title of dampness. Tho decay caused by dampness, as in the ease of dryrot, is effeetnally prevented by the presence of water or by a constant enrrent of air, whether perfeetly dry, or saturated to any degree of hnmidity. Dampness, therefore, is uot the mere presenee of moisture in the ordinary formin whiel it is held in solution by theatmosphere. If an hygrometer’were placed in a damp situation it would simply indicate perfeet saturation ; no ovaporation wonld take plaee, but the eottou eovering of the wet bulb will be speedily covered by a peculiar mould, well known by its fanguslike odor, and iu a short time it will he converted into an impalpable powder, or ash, Under similar circumstances timher, leather, paper, and all like materials underfo the same rapid decomposition; vegetxble gums and oils, that are insoluble in water, and even dry hard paints and yarnish, becomo soluble and liquid. Massive timhers are rapidly disintegrated, entirely losing their weight, though still retaining their form ; and they are often totally free from apparent moisture, altbough at times dotted externally by drops of brilliant water. Damp spots are, moreover, peeuliarly hygrometic, indicating atmospheric changes with remarkable precision, and temporary desiccation in no way disturbs this precess. The peculiar odor which always accompanies this eondition is one of the best tests of its existence; and the ex_ pression that a room smells damp is strictly correet. Theeffect is, within certain limits, intensified by increase of temperature and absenee of light, and arrested hy poisons destruetivo to vegetable life. If this phenomenou of deeay is more elosely examined the process would be found to resemble, in many respects, a slow combustion. The ultimate results of combustion and .deeay are strikingly similar ; the union with oxygen is slowly effeeted, and the residue is more or less diluted with foreign substances ; but whether bodies are burned or deeayed the remains, in thoashes, are substantially identical. Deeay may thus, to a great extent, be looked upon as a decomposition, resulting from the slow chemieal combination of oxygen witb the matters deeomposed. Now, if slow combustion is the eause of decay, and that particular state called dampness is so important an aecessory, tho inquiry naturally suggests itself: What connection exists betweeu those agencies, or in what way eau damp promote the absorption of oxygen? In tho case of organic substances, the presence of vegetation in the form of fungns, or mold, is an invariable characteristic of decay, and the decomposing effect of all vegetable growth is beyond question. It may be said, that the vegetable growth alluded to is the effect rather thau the cause of deeay. Doubtless, the spores of microseopic fungi followed the law of all other seeds in vegetating only under the peculiar Conditions of soil, light, and moisture which were adapted to their growth ; dampness and partial darkness, and absolute quietude, and even deeay, may bo essential to their existenee ; and, therefore, itis only under such conditions that they appear at all. But, nevertheless, when they do appear, their preseneo rapidly aecelerates deeay, and they furnish a vital medium, capable of accomplishing tho observed effeet—eombustion, or slow union with oxygen, of the substauees on which they thrive. It is probably by some sueh chemical vital action that tho faet can be explained, why even tho hardest roeks aro rapidly dosomposed by the growth of lichens, or that deeay should be arrested by poisons whieh econld exert no other infiuenco than the prevention of vegetation. It was equally remarkable that in the putrefactiou, or rapid ehemien] decomposition of animal und vegetable substances the same profusion of tho lower forms of animal, us well as vegetable, organisms eharacterize the phenomenon, Whatever may he the enuso of deeny, moisture is an indispensablo element, Dry air is inenpablo of deeomposition. Water ;isa earrier of oxygen iu a potent form ; and it was only from water, aud more espeeially when iu tho form of vapor, that the oxygen necessary for decay ean be obtained. The durability of tin and iron roofs in Geneva and St. Potersburg is dne to the absenec of moisture ; and the importance of some shelter for timber, and of thorough ventilation, wherever it is employed in a moist elimate, is a neeesssry eorollary. We shall next week eontiuuo our notes on that portion of the paper of Mr. Clarke, wherein he speaks of the durability of nretals, Magnet Test of Iron---the other Side. _ Mr. Jolin Farquharson, of Her Majesty’s Dock-yard, Sheerness, sends a paper to Engineering, ix which he takes a different view of tho above-named subjeet from that advaneed by Mr. Saxby, of whose eonelusions we gave asumming-up two week since. It will bo rememhered that oue of these conclusions was, that free magnetism was not confined to the surface of a body, but distributed thronghout the mass, Mr. Farquharson, after refuting certain other positious by Mr. Saxby, takes up this one, and closes his paper with the following remarks upon it: “The amount of free magnetism in iron is not direetly as the mass, nor exactly as tho surfaee, although nearly so. Barlow found that a sbell 10 in. in diameter and 1-36 in. thick, had two-thirds the magnetism of a solid sphere of that diamcter; and aceording to Poisson’s formule, a cylinder 10 ft. diameter and 474 iu. thiek has as much free magnetism as a solid cylinder of that diameter; but it has been objected that this is only true when the continuity is regularly interrupted—a condition not to be anticipated in aetual practice, and I havo endeavored to test this experimentally with tho following result: A cylinder 4 in, long, Zin. diameter, and 4 in. thick had a cylinder of iron borings roughly fused together by molten iron inserted, and slowly revolved within the hollow cylinder; the needle was perfeetly steady and unaffected. The like resnlt followed the suhstitution of a solid and also the half of a solid cylinder of the same deseription of iron tor the rough cylinder of borings, the defleetion in either case remaining the same. It appears, therefore, that tho free, magnetism acting upon a needle is due to a stratum cf iron near the surface, and that considerable irregularity iu the internal structure of a bar of iron 2in. thick may exist without affecting the needle. But the praetice, so far as I have seen, is to use a very light noedle near the surface of the iron, and to disregard altogether the induetive influence of the needle. Now a cylinder of the thinnest iron that can bo produced will defleet a needleso used 90°; a solid mass can do no more, and I can see no reason why we should not find the same varieties between this and the ueutral point, where deflection is uil. We must, therefore, it appears to me, remain quite uneertain as to the condition of the internal mass at a greater distanco fromthe needle.” Puantne-Macuinr Breps.—Au idea has been advaneed that the beds of planing machines should he reversed onee a year

where their construction pormits it. This will equalize the wear of the slides and make them truer than they wou!d otherwise be. Carclessuess will often in twelve months so injure 2 planiug machine that nothing willcure it but being made over. If, however, the artisan be up to his business, ho will so arraugo his work on the bed that it will wear true at all times; if he is obliged to work auy leugth of time on one end of the bed, le ought to divido the periods so as to run first one end of the platen over the slides and then change tho other end. In this way the best results will he obtained. Scelentifie Miscellany. "The Heating Power of the Moon. Myr. Harrison reeeutly read an interesting paper before tho British Royal Astronoimical Society on the capacity of tho moon to receive heat from the sun and to radiate the saine intespace. Assuming that the lunar surface hns a capucity for heat, equal tothe surfaee of tho earth, that luminary must, during its long lunar day, of uearly filteen of onr days and nights, storo up on any giveu snrfaee exposed to tho action of tho sun’s rays during that leugth of time, a very large amount of heat. he moon’s hemisphere, visible to ns, would Le heated to its greatest possible extent during tho third or last quarter, whon the half moou thus illuminated has been subjected to the eflects of solar radiation for a mean duration of about eleven days, and the remaining half, then in shade, has recently been receiving the sun’s rays for a period of equal duration. Hence, if the moon radiates heat as farinto space as to reach the earth, it would be at that time that our planet would be reeeiving its maximum of hoat from its satelite. Now the heat thus assumed to be acquired by the moon, and radiated into space, is dark heat; andas it is known that the aqueous vapor in the atmospbere has a power of absorbing dark heat, says Mr. Harrison, hence, the heat radiated by tho moon, instead of conveying warmth to the earth’s surfaee, is employed in heating the aqueous vapor in the atmosphere above the clouds. Tho clouds would thus be raised toa higher elevation, and of course to a greater or less extent dissipated. There would also be a sensible fall iu the temperature near the earth’s surface caused by such eyaporation or rarifieation, Myr. Harrison further stated in his paper that the daily mean temperature at the Oxford, Berliu aud Greenwich observatories, when reduced to tables, according to tho age of the moon, show that the temperature of the air near the surface of the earth is affected by the moon in the mauner aboye deseribed; and that the maximum mean temperature oceurs about the seveuth day of the lunation, and the minimum after the full moon, These results, if as stated, would be re‘markably confirmatory of Mr. Harrisou’s views, We may here remark that the editor of the London Quarterly Journal of Science, differs from Mr. H. ‘The editor holds that the moon does indeed exert a marked influence, but ot for the reasons assigned by Mr. Harrison; but because that influence is exerted (in consequence of the varied times at whieh the moon reaches ber meridian) at more or less favorable hours of the day—such hours as those in whieh the hygrometrieal state of the atmosphere, whieh varies at different hours of the day, is most favorable for the development of such phenomena, As respects the heating of the moon’s surface, tho Quarterly remarks that, although thero is undoubtedly an enormous quantity of heat poured upon a lunar hemisphere, in the courso of the long lunar day, yet we have.no means of knowing how that heat is disposed of. Nearly all of it may be radiated into space, or a large portion may be consumed in effeeting changes —as of solid into liquid, or of liquids into vapors—followed by a return to the original state during tho equally long night whieh follows. The Qzarterly thinks it bardly possible that the heat stored up in the moon during its day, beeomes sensible tous, by radiation, during its following night; but rather far more probable that the heat we aetually reeeive {rom the moon is from refleetion, procisely as we reeeive her light. Iv has been found that steel rifle-barrels when fired off several times in a northerly direction, aequire magnetic propertie +. Cotor Ix Astronxomtcan OBSERVATIONS. Mr, J. Browning, F. I. A. §., has published a paper in the Chemical News, in which ho shows quite eonelusively thatthe difference in tho apertures of different teleseopes affects materially tho appearance of the heavenly hodies to the observer. The eolor of a given star, or of the moon during au eclipse, ete., appears very different to tho observer wheu he ehanges his teloseopo from a four toa six or seven ineh aperture. From this it follows that the estiniate of eolors, in astronomieal observations, must bo coupled with the diameter of the aperture of the telescope through whicli the ohservations are made, For instance, the small star in the eluster Perseus, appears of an indigo-blue with an 8% ineh, Prussian-bluo with a 104 inch, and royal-blue with a 15'{ inch aperture. This diseovery accounts for some most singular discrepaneies notieed by observers, whieh have beretofore been attributed to color blindness, Curuustry or Writinc.—Writing ink, with trifling variations of proportious, is a compound of sulphate of iron, extraet of galls, and gnw, held in mechanical union by soft wator. When tho fluid is applied to the paper, the following ehemieal actiou oeeurs: The oxygen of the atmosphere forms gallic acid with the tannin of tho galls, whieh, iu turn, unites with the iron in solution, forming a black precipitate (the per-gallate of iron), and the sulphuric acid, thus set free, enters the body of the paper, while the water passes off by evaporation. When the presence of this sulphuricacid in tho tissue of the paper is in excess, the paper is gradually destroyed. It should be the aim to obtain an ink which will leave tho least acid in the tissuo, and still give a permanent black color. Expansipinity oF Bismure.—Bismuth is a metal which, unlike other metals, expands on fusing or cooling. Mr, A. Tribe recently read a paper before the London Chemical Society ‘‘on the Freoziug of Water and Bismuth,” in which the author made mention of a series of experiments whieh proved that, although bismuth, like water, increases in bulk on freezing; yet this increase is only at the moment of congelation. Thisis no evidence that, as is the case with water, any expansion tales place before solidification. Srrctra oF Merrzors.—Mr, Browuing has invented an ingenious contrivance for reducing the angular velocity of meteors so as to enable him to obtain their spectra. With this deviee he has found it easy to ohtain the spectra of balls shotfrom a Roman eandle—the characteristic lines of baryta, strontia, etc., can be readily distinguished in their spectra. : Buow-Prrer Braps,— Prof, G, Rose has studied some curious phenomena exhibited by eortain blow-pipe beads. He finds that tho opacity which they frequently assume on eooling, results from the separation of mieroscopic crystals. The Professor’s researches on the reaetion of titanic acid appear to have some bearing on the natural formation of anatase. Trunprr Mapr Visreue.—Dr. Topler foealizes a ray of light on the object-glass ot a telescope, whieh is conueeted with a screen in sueh a way that any disturbanee of the air becomes visible; foriustanee, the intense sonorous vibrations of the atmosphere produced by electric explosions show themselves in the teloseope as visible rings or cireles of light.Discovery 1n Maanntism.—M. Gerard has discovered a vory curious faet. If a metallie ring made of wire, the diameter of which varies regnlarly, so that at one side of the ring itis very thin and atthe other side relatively very thiek, be suspended over an . eleetro-maguet, it will begiu to revolve. The author sees in this fact the germs of a . new system of eleetric telegraphy, for the . details of whieh we wait.