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OUR ASTRONOMICAL COLUMN.
ASTRONOMICAL OCCURRENCES IN APRIL 1898 :-
April 3. Pallas 15' south of o Eridani (mag. 4'1).

5-15. Mercury well visible in the evenings near Venus.
9. Juno (mag. 8.7) in opposition to the sun.
IO. 13h. Mercury at greatest elongation (19° 23′ E.).
10. 14h. 38m. to 15h. 8m. A Ophiuchi (mag. 47) oc-
culted by the moon.

10.

14.

15.

99

".

Saturn. Outer minor axis of outer ring = 18" 14. 5h. 51m. to 8h. 26m. Transit of Jupiter's Sat. III. Venus. Illuminated portion of disc o'968. 15. Mars = 0.953. 16. 9h. 4m. Minimum of 8 Persei (Algol). 18. Mercury and Venus in conjunction (Mercury 3° 20′ N.). 19-20. Meteoric shower from near a Lyra (radiant 270° + 32°).

9h. 11m. to 11h. 49m. Transit of Jupiter's Sat. III. 15h. Mercury in conjunction with moon (Mercury 2° 2' S.).

21. 21.

27.

79 Geminorum (mag. 6·5)

6h. 41m. to 7h. 44m. occulted by moon. 28. 12h. 34m. to 15h. 15m. Transit of Jupiter's Sat. III. 29. 13h. Im. to 13h. 15h. § Leonis (mag. 5'2) occulted by moon.

FAVOURABLE APPARITION OF MERCURY.-The most convenient period in 1898 for observing Mercury will be during the fortnight from April 5 to 18, when the planet will become visible about an hour after sunset above the W. by N. horizon. He will reach his greatest eastern elongation on the morning of April 11, and will set on several evenings at about this time, a little more than two hours after the sun. Fortunately, at this special period, the planet will be situated within a few degrees of Venus, and the latter will form a brilliant guide to the position of Mercury. On April 5 Mercury will be apparently 6 degrees above Venus, and on ensuing nights the interval decreases until on April 18 the two objects will be in conjunction, Mercury being about 3° 20' N. of Venus. Mercury will then appear on the north-west side of Venus, but is likely to be much fainter than before elongation, as he rapidly loses brightness owing to the crescent-phase which his disc assumes. The following are the times of setting of the sun, Mercury and Venus, and the intervals at which Mercury sets after the sun :

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18

Date 1898.

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Mercury Venus

sets.

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h. m. 8 28

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48 47'1

2 = 263 164 18980

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33 7 48

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Elements.

T = 1898 March 18.501. Berlin Mean Time.

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The conjunction of Mercury and Venus on April 18, at about 5h., does not appear to be mentioned in the Nautical Almanac.

COMET PERRINE.-Dr. F. Ristenpart has calculated the elements and ephemeris of this comet from the observations made on March 19, 21 and 22. These, as given in Circular No. 3 from Kiel, are as follows:

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The first of these stars, whose position for 1900 is R. A. 19h. 32m. 15s., declination + 20° 6' 6, has a period of nearly eight days, the light curve varying from mag. 69 or 70 at maximum to 76 at minimum; the epoch for the calculation of the maxima being 1897 October 2'47 Greenwich mean time. The light curve shows small secondary variations both in the ascending and descending portions, the rise to maximum and fall to minimum Occupying equal intervals of time.

The second variable, whose position for 1900 is R. A. 19h. 40m. 49s., declination + 29° 1′2, has a period of 3 844 days, the magnitudes at maximum and minimum being 66 and 7'4 respectively. The dates of maxima can be calculated from the epoch (maximum) 1897 October 4'66 Greenwich mean time + 3844 E. In the case of this star the curves on either side maximum are not equal, but the rise to maximum comprises less time than the fall to minimum. The former occupies only 09 days, while the latter takes 29 days. The curve is described as similar to Cephei. The observations suggest that on the downward side of the curve, 175 days after the maximum, the light becomes stationary for a short period of time, afterwards decreasing to the next minimum.

VARIABLES AND THEIR COMPARISON STARS.-Variable star observers may be glad to know that Prof. E. C. Pickering is able to furnish the photometric magnitudes of a great many comparison stars for long-period variables, and that he will communicate the information in advance of publication should any one require it (Harvard College Observatory Circular, No. 27). Sequences of comparison stars have been selected for about one hundred variables, stars brighter than the tenth magnitude having been measured on at least three nights with the meridian photometer, and those from the eleventh to the thirteenth magnitude on two nights with the photometer having achromatic prisms. Observations are already completed for the following stars ::-T Andromeda, T Cassiopeia, R Andromeda, S Ceti, S Cassiopeia, R Piscium, R Arietis, T Persei, o Ceti, S Persei, R Ceti, U Ceti, R Tauri, S Tauri, R_Auriga, U Orionis, R Lyncis, R Geminorum, S Canis Minoris, R Cancri, S Hydræ, T Hydra, R Ursa Majoris, X Virginis, R Comæ, T Virginis, Y Virginis, T Ursa Majoris, R Virginis, S Ursæ Majoris, U Virginis, R Hydræ, S Bootis, R Camelopardali, U Herculis, W Herculis, R Ursa Minoris, R Draconis, x Cygni, S Cygni, R Delphini, U Cygni, V Cygni, T Aquarii, T Cephei, S Cephei, SS Cygni, S Aquarii, R Pegasi, S Pegasi, R Aquarii, and R Cassiopeia.

Prof. Pickering adds that the brightness of each of these variables is being determined monthly by Argelander's method, and it would be a good thing if other observers would reduce their observations to the same scale of magnitudes, as then the desired uniformity in results would be obtained.

The variability of the star in Aquila, R.A. 19h. 333m., Decl.+ 11° 29′ (1900), announced recently by the Rev. T. D. Anderson, has been corroborated by an examination of the Harvard photographs. Measures of fifty-seven negatives gave the maximum brightness 92, and minimum less than 129. The variations can be closely represented by the formula J.D. 2411550 + 330 E.

1

CONCAVE GRATINGS FOR STELLAR PHOTOGRAPHY.-Some experiments have been carried on quite recently at the Johns Hopkins University to investigate the value of the use of concave gratings for stellar spectroscopy, and the results obtained bid fair for further trials (Astrophysical Journal, vol. vii. No. 3, March). The methods originally suggested by Prof. Rowland have been developed; Dr. Poor has derived the formulæ, and directed the construction of the apparatus, while Mr. Alfred Mitchell has made the experiments and photographs. The method finally adopted was the direct one, the grating being the objective and spectroscope combined; the light from the star was thus reflected directly from the grating to the photographic plate. The best position for general work was found to be that in which the centre of the photographic plate falls on the axis of the grating. From the simplified general equation

ρ

I + COS V

in which p is the radius of curvature of the grating, R and the spherical coordinates of the light source, and r and u those of the curve on which the spectra are brought to a focus (R being ∞ and μ = 0), it was found that those parts of the spectra where cos μ could be assumed equal to unity, were brought to a focus on a circle whose radius is given by the above equation. The equation really represents a parabola, but within certain limits the spectrum may be considered normal. For a grating of medium dispersion, the entire spectrum will be practically normal; but with one giving larger dispersion, as a Rowland 21-foot, the scales of the middle and end differ by one and onehalf parts in a thousand at a distance of 3° from the axis. It is necessary, therefore, that parabolic curved photographic plates must be used, but within certain limits they may be circular. In the experiments a small Rowland concave grating, of 15,000 lines to the inch, radius of curvature one metre, and ruled surface 1 x 2 inches, was employed, the photographic plates being bent to the proper radius. The spectra of Sirius, Capella, and Rigel obtained were 5 cm. long, and from o'I mm. to 15 mm. broad, and showed many lines.

Thus with an exposure of forty minutes, the spectrum of Sirius showed "16 hydrogen, H and K lines, and 15 other distinct fine lines." Capella, with forty minutes' exposure, gave F.G.h. H. K., and about fifty fine lines. It may be mentioned that these experiments were made on the fifth floor of the Physical Laboratory," subject to the jar of street-cars and city traffic, as well as to dust and to the glare of electric lights," so that the results were not obtained under the best conditions.

A CATALOGUE OF 636 STARS.-No. 4 of the Mittheilungen der Hamburger Sternwarte contains a catalogue of stars observed by Herr W. Luther in the years 1885-92 with the meridian circle of the Hamburg Observatory. The observations in R.A. were made after the eye and ear method: those for declination by bringing the stars between two horizontal wires. The positions have all been reduced to the year 1885, and a comparison is made with the catalogue of the Astronomische

Gessellschaft Zonen.

THE PREPARATION OF MARINE ANIMALS AND PLANTS AS TRANSPARENT LANTERN-SLIDES.

AT the request of the editor of NATURE, I give an abridged account of my essay in the volume of original researches published to commemorate the establishment of the Sheffield University College by Royal Charter in 1897. I shall confine myself mainly to the animals shown in the reproductions from four of the series of photographs taken by Mr. J. E. Atkinson, of our College, from some of my slides. Though on the whole these reproductions show the general facts fairly well, much of the minute detail is unavoidably lost, which is quite distinct when the mounted animals or photographs are somewhat magnified.

It is about eleven years ago that I first attempted to prepare lantern-slides with marine animals. At first I did not mount them in balsam, but very soon found that this is in almost every case not only desirable but even essential, since they so readily become mouldy, sometimes are attacked by mites, and are often far too opaque. Some also scale off from the glass and break to pieces, unless mounted. The success of the preparations depends almost as much on the proper mounting with balsam as on anything else, and sometimes the only way to get

excellent results is to mount several, and pick out the best, which perhaps cannot be known until the specimens are finally mounted in balsam.

The methods necessary in mounting vary greatly in the case of different animals. Often little else is wanted than to arrange them properly on a lantern-glass, so that they touch it more or less completely all over their under surface, and then to drain and dry them. Many readily adhere round the drying edges, before the central parts are dry; and being thus fixed, they do not shrink laterally on further drying, but merely become thinner. On finally drying completely they may partially scale off, and it may be desirable to gum them down in one or more places, lest they should become loose when mounted in the balsam. There are a few animals that will not adhere at all to the glass, and yet shrink greatly. This circumstance has so far prevented me from making satisfactory slides of Actinia. I have succeeded with every other group.

Few animals are more easy to prepare than small flat fish like soles and dabs, 2 or 24 inches long. These are killed by putting them into dilute alcohol, and arranged on the glass as soon as dead, whilst still limp. The chief matter is to arrange out the fins neatly. These soon dry, and adhere well; but in order that the side near the glass may keep flat, it is desirable on further drying to adopt a plan which I find most useful in many other cases. Very few, if any, animals will adhere in an objectionable manner to thin paper soaked with bees-wax, and, having laid such over the animal, pressure can be applied. What is wanted is that this pressure should be fairly uniform, and not merely on the thick parts. This is easily done by having a stout lantern-glass covered by two or three thicknesses

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FIG. 1.-Priapulus in natural state.

of fine thin flannel, which is pressed down by a smaller or larger weight, so regulated as not to crush or distort the animal, but rather to retain as much as possible the natural shape and show the internal structure. The animal then dries through this flannel, and at the same time keeps sufficiently flat on the glass. Finally, any specially high parts can be pressed down by using a flat glass without flannel and a heavier weight.

A considerable variety of marine worms can be made into most excellent transparent slides, showing not only their general shape and colour, but also much of their internal structure. Sabella may be named as a specially good example. Such animals should be killed by keeping them for a short time in dilute alcohol. The aim should be to dry them before partial decomposition sets in and destroys the small blood-vessels. If all goes on well it is possible to dry and permanently preserve such worms as Nereis, so as to show not only the chief bloodvessels but even the smallest branches, and the blood may retain its red colour for years without any apparent change.

As an example of an animal mounted without staining, I give in Fig. 1 a reproduction from Priapulus. It should be killed by putting it into fresh water, and left in it so long that the body just begins to get limp. It can then be easily arranged on the glass, and adheres fairly well without lateral contraction. If mounted at once or previously kept in alcohol the body is too hard and will not adhere to the glass, and on drying contracts so much laterally as to become very unlike the living animal. The internal anatomy and general structure are best seen by cutting the animal open from end to end, and staining the whole with Beale's carmine or Kleinberg's hæmatoxylin. When thus

prepared, the muscular structure of the body-wall and the general internal anatomy are seen to great perfection.

I have not yet succeeded in preparing specimens of Arenicola when in their natural condition, so as to show their internal structure well, but have made some most excellent preparations by carefully cutting the animal open from end to end, spreading it out on the glass, and displacing the intestine and its appendages so as to be quite clear of the body, but yet to show the numerous blood-vessels passing to the lateral branchiæ from the main trunks along the intestine, which, however, are imperfectly seen in Fig. 2, which I give as an illustration of what may be done by partial dissection. Of their kind no preparations could be more satisfactory than some thus made, since the general anatomy is seen to great perfection, and the colour of the blood has remained unchanged for years, though in other cases, from some unexplained cause, it quickly turned brown.

It was the desire to preserve some of the beautiful Nudibranchs that led me to mount animals on slides. The lovely purple Eolis quickly loses its colour in alcohol. It should be killed in dilute alcohol, but kept in it a very short time, and then arranged on the glass and nearly dried. A strong solution of gum should then be placed over it, and the whole kept damp over diluted alcohol, to enable the gum to soak well into the animal, so as to protect the pigment from the balsam, in which it is soluble. I have specimens which have been mounted for more than seven years without showing any further change than the loss of a bluish tint, which occurs almost at once.

Most excellent transparent slides may be made with the so-called spider crabs, and these sometimes show well the

FIG. 2.-Arenicola partly dissected.

manner in which they are covered with a growth of sertularians, sponges, ascidians, &c. The animal is properly arranged on the glass, and at first gentle, and afterwards stronger, pressure applied, using waxed paper and glass covered with flannel; by which means the whole may be pressed flat without material distortion. The body and legs may indeed be made a little wider than natural, but this is to a great extent counteracted by lateral shrinking. At all events the general results are extremely good, and the muscles in the legs well seen.

Various species of Mollusca can be prepared so as to show their general anatomy by dissolving away the shell with hydrochloric acid in diluted alcohol. The organic matter of the shell retains the natural form, and shows the attachment of the various parts of the animal, which may be stained or not according to circumstances. Judging from what I have done, it will be possible to prepare instructive slides from the shells alone of some species, by dissolving away the carbonate of lime and mounting the membranous residue, which retains the natural form and much of the colour.

When first I attempted to mount Medusæ as lantern-slides, I looked upon them as most unpromising, and never imagined that it would be possible to prepare such specimens as I now possess. The first step must be to dissolve out all the included salt. For some years I used to put the newly caught specimens of Aurelia into methylic alcohol, diluted with half its bulk of fresh water, and after leaving them in for some hours, with occasional movement so as to prevent adhesion to the glass, they were digested over and over again with fresh diluted

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alcohol. Specimens so prepared are so colourless and transparent that little of the general structure can be seen, but if kept many months in alcohol they turn somewhat brownyellow and show their structure moderately well. On the whole it is, however, better to stain them. I have experimented with a great variety of colouring-matters, but find that the best are tincture of madder, Beale's carmine, methylene-blue, port wine, and tincture of galls. The canal-system and the general structure are well seen when Beale's carmine is used, but the colour is unnaturally bright, whereas the colour of madder is more in harmony with nature. Methylene-blue gives good results with fresh specimens, but does not stain those which have been kept long in alcohol.

Though I have many splendid specimens prepared as described, my last year's experience shows that, at all events for some Medusa, a 4 per cent. solution of formic aldehyde is far better than alcohol. Into this the newly-caught animals were at once put, and it was subsequently used to dissolve cut the salt. The superiority of this over alcohol is that Medusa retain their form almost unaltered, and the most delicate parts can be moved about and arranged without fear of tearing. The only serious objection is that the very delicate fringe of Aurelia may be too rigid to be properly extended. No such objection exists in the case of Cyanea or Chrysaora; and Cyanea may be stained so as to be of nearly the natural colour, which is other

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FIG. 3.-Aurelia stained with carmine.

wise lost. In Fig. 3, I give an illustration of an Aurelia stained with carmine when in a 4 per cent. solution of formalin to which a little sulphurous acid was added.

In mounting Meduse some special methods are necessary. Having removed the salt and stained the specimen as thought desirable, the lantern-slide glass is put into one of the usual developing dishes, and the animal floated out, and to some extent properly arranged, when under the liquid. The specimen may then be half an inch thick in the centre. No attempt should be made to dry it at once, since the greater part of the included liquid usually diffuses out, and nearly the whole can be drained off by keeping the slide inclined and covered up so as not to dry. In some cases the liquid passes off badly, but comes off rapidly, if a solution of gum is spread over the animal. As the edge dries, it should be covered with a strong clear solu tion of gum to which a little glycerine has been added to make it less brittle when dry, and this process continued until the whole specimen has been covered with gum. It should then be kept for some days in a wet state, so that the gum may soak well in, and any small bubbles not easily removed mechanically may disappear by absorption. At first I used to keep the specimens in a developing dish over a little water, covered up with a closely-fitting plate of glass, but sometimes in the course of a single day they became coated with a long growth of mould.

If, however, instead of water they are kept over alcohol diluted with an equal volume of water, they may remain wet for weeks, without any such growth of mould or such alteration in the gum as is produced by the action of stronger alcohol. It is very desirable not to finally dry too quickly, but, as it were, to anneal the specimens; since contraction may give rise to sufficient tension to cause them to crack and scale off from the glass.

I must now consider cases in which it is desirable to get rid of part of the colouring-matter, either natural or developed on keeping. Diluted sulphurous acid is very useful for this purpose, and remarkable results can be obtained with small fishes. If plaice about 24 inches long are kept in alcohol and then for a few weeks in diluted sulphurous acid, the earthy matter of the bones is dissolved out and only cartilage left; the general colour is reduced, and the thickness diminished; but strange to say, the arteries and enclosed blood are so little altered that when the specimens are mounted the aorta and branching arteries are well seen over the whole animal, as shown in Fig. 4, which, however, fails to show the more minute arteries, quite visible in the original.

FIG. 4.-Plaice treated with sulphurous acid.

I must now conclude by describing the methods employed when finally mounting the specimens in Canada balsam. At the four corners of the glass should be gummed small pieces of blackened cardboard, of such a thickness that the cover-glass will just clear the object and not rock. The glass with the animal should be kept for a short or longer time in benzole; and, in the meanwhile, the cover-glass should be warmed on a suitable stand over a small burner, and a fair quantity of liquid balsam placed in the centre. The glass with the animal is then taken out of the benzole, and carefully placed over the balsam, so as to catch up as few bubbles as possible, the benzole causing the greater part to burst and disappear. If too little balsam has been used, more is easily run in between the glasses; and if only a few bubbles have been caught up, they soon disappear. If there are more than desirable, they can be got rid of by keeping the slide slightly inclined until they rise to one edge and can be removed. After keeping cold for a few days, for the balsam to harden the edges, it should be bound round with thin paper of the best quality, made thoroughly wet with gum. When this dries, contraction may squeeze out some superfluous balsam. This paper should then be varnished, and finally strips of good black paper should be glued well round the whole. All possible care should be used to enclose the balsam thoroughly, so as to avoid its turning yellow, and to prevent leakage, when the slide becomes warm in the lantern.

I have, however, had scarcely any trouble from this cause, since I have so completely fastened it in that the glasses or binding yield sufficiently. I may also say that though many of

my slides have now been made for more than seven years, I have not observed any deterioration, but, on the contrary, many have greatly improved owing to the balsam having more completely penetrated into the tissues, and the included air disappeared. When this has taken place, the specimens are far more transparent and show their structure far better than the living or dead animals. Nearly all my slides have been kept in the dark, but some have been kept about the same time in a strong light at the Sheffield Public Museum, Weston Park, and, as far as can be judged, have not faded, even when imperfectly mounted. H. C. SORBY.

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OUR MINERAL WEALTH.

IT would be difficult to conceive of a more concise and clearly expounded compilation of statistics and general information regarding mines and mining than that presented in the Third Annual Report upon the Mineral Industry of the United Kingdom of Great Britain and Ireland, which has been issued by the Home Office in the form of a Blue Book for the year 1896. The volume before us is a synoptical review of the condition of our own mineral industry, as well as that of other countries, which reflects unbounded credit upon its author, Dr. Le Neve Foster, and those who have assisted him in the work. It is divided into six parts, under the respective titles of persons employed, output, accidents, prosecutions, general remarks, and mineral statistics of the Colonies and foreign countries. It contains, in addition, nineteen appendices, and concludes with an exhaustive index.

The statistics for the United Kingdom distinguish between mines or underground workings and quarries or open workings; and the same figures are marshalled again and again under different aspects, so as to show their varying significance when coalfield is compared with coalfield, inspection district with inspection district, and county with county.

The first four parts include sixty-nine tables, in which the various classes of information susceptible of being so dealt with are compared with each other and with the corresponding figures for the year 1895. These are followed by six diagrams, on which are shown by means of curves, extending from 1851 to 1896 inclusive, the yearly variations in the numbers of persons employed above and below ground; the output and export of coal; output, export, and import of iron ore; deaths due to accidents generally; deaths from accidents, arranged in five distinct classes (explosions, falls of ground, in shafts, miscellaneous, and on surface); and the average quinquennial death-rate per 1000 persons employed, classified in the same way as in the last case. In Part iii. short descriptions are given of the circumstances under which the most important accidents of the year occurred; and throughout the volume many pertinent remarks are made, which serve to throw light upon the construction and meaning of the tables, point to the conclusions which they justify, and infer the lessons that are to be learnt from their perusal.

Turning now to a consideration of the subject-matter, we find that, taken altogether, there were 725,803 persons employed in or about mines during the year under review-576,325 working in the mines, and 194,478, including 5114 females, working on the surface. Of these numbers 678,690 were employed at 3260 coal mines, 16,819 at 136 iron mines, and 30,294 at 720 other mines. In addition to this there were 112,829 persons employed at 7758 quarries.

The quantity and value of the principal classes of minerals mined and quarried were as follows:

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The total value of all the minerals worked in the kingdom was 69,088,3667., from which it will be seen that the value of the coal alone was practically five-sixths of the whole amount.

The number of separate accidents in mines was 886, involving the loss of 1065 lives, of which 147 were the victims of four explosions of fire-damp or coal-dust. The number of separate accidents in quarries was 117, in which 124 lives were lost.

A comparative table showing the death-rates from mining and quarrying accidents in different countries per 1000 persons employed, brings out some remarkable facts. Taking the column which represents the total for underground and surface for the year 1896, or in the absence of the figures for 1896 those of 1895, we find the following rates for the coal mines in some of the principal coal-producing countries of the world :—

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According to M. Louis Lacombe, who compared the deathrates from accidents in mines in quinquennial periods, the last of which was 1890 to 1895, the ratios are as follows:

:

Russia 2-90, Belgium 2·38, England 2:18, France 1*37. The death-rate from accidents to railway servants in the United Kingdom for the year 1896 is given as I'01 per 1000. The category includes such classes as carmen o ̊47, clerks 0'17, mechanics o 33, and signalmen o'55, whose occupations are not by any means dangerous. On the other hand, the death-rate amongst those who have to do with coupling and uncoupling and making up the trains is infinitely more serious, such as shunters 4'94, yardsmen, 3'27, guards and brakesmen of goods trains 3:03. The highest of these figures pales before those applicable to sailing ships, amongst which we find :—

39

99

British sailing ships (1896) German (1893).. These figures prove conclusively that the miner's calling, when brought into comparison with some other kinds of employment, is not of such a dangerous nature as is generally supposed. As having a bearing upon this question, however, it may be stated that one of the most gratifying features of the report is the curve given on Plate 4, which shows the death-rate per 1000 persons employed underground in coal-mines to have been reduced from the appalling figure of 5.5 in 1851 to 162 in 1896. This result-upon the attainment of which the Home Office, the Inspectors of Mines, and the mining community generally may well be congratulated-is undoubtedly due to the efforts that have been made by means of legislation and inspection to remove the causes which formerly led to such a lamentable loss of life. The loss of 147 lives in four great explosions in the year 1896 is a black spot in the record which ought never to have been there. I am glad to observe that the year 1897 has been entirely free from anything of the same kind, and I feel confident that if the new regulations regarding the watering of dusty places, and the use of explosives are attended to, or enforced with unflinching severity, we shall have seen the very last of such affronts to humanity and common sense.

The fines imposed upon owners and managers of mines for contraventions of the Mines Acts amounted to the insignificant | sum of 2587. 135. 9d., while the workmen for similar offences paid 4597. 6s. 8d.

The outputs of coal from a few of the principal coal-producing countries were as follows:

:

12'9 15.8

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Acetylene was first isolated by E. Davy in 1837 from potassium carbide, a by-product of Sir II. Davy's method of manufacturing potassium. In the middle of the century Berthelot investigated its properties, and Wöhler produced it from calcium carbide. During the past few years it has assumed commercial importance owing to the development of the electric furnace, in which calcium carbide can be readily produced from lime and carbon. The furnaces used consist essentially of crucibles with carbon rods forming the positive electrode and a bottom plate lined with carbon for the negative. In the more recent furnaces these crucibles are mounted on small trollies so that they may be run out of the furnace when ready and a fresh one inserted without loss of time. The carbide formed is a hard, dense substance of reddish colour, unacted upon by most of the ordinary reagents. It is, however, rapidly decomposed by water into acetylene and lime, giving 5'9 cubic feet of acetylene, at a temperature of 60° F. and a pressure of 30 inches of mercury, per 1 lb. of carbide. As the power required theoretically to produce 1 lb. of calcium carbide in an electric furnace is more than 2 H.P. hours, its manufacture is at present restricted to localities where power is cheap, as for instance where water-power is available.

soot.

Acetylene is a colourless gas with an intensely penetrating odour, and is slightly soluble in water, and extremely so in some other fluids. It is endothermic, giving 407 calories per cubic foot, whereas theoretically its value is 336'5 calories. As an illuminant it gives the most brilliant light of all gases, 5 cubic feet per hour under suitable conditions giving 240 candle-power. For small consumptions, however, this value is not obtained, and ordinary burners after a short time became clogged with The latter defect can be overcome by the use of an injector burner, which, however, requires a higher pressure. Various diluents have been suggested, but have not been tried on a practical scale. The flame has a high actinic value, and causes light colours to appear lighter, and dark colours darker than when exposed to sunlight. The gas, when inhaled, combines with the hæmoglobin and renders the blood incapable of taking up oxygen, and thus causing suffocation. It has, however, been shown that it is no more dangerous in this respect than coal gas. Acetylene unites with copper, in the presence ammonia, forming copper acetylide, and this when in a dry state is violently explosive. Silver is similarly acted upon.

moisture and

Owing to the difficulty of obtaining the materials used in producing calcium carbide in a pure state, phosphoretted and sulphuretted hydrogen and ammonia are often found in the gas, and these should be removed by passing the gas through water and an acidified solution of a metallic salt. Nearly all proportions of air and acetylene are explosive, the gas itself being decomposed at 780° C. At higher pressures than 2 atmospheres, if this temperature is attained by a part of the gas, it is communicated throughout the whole mass and a violent explosion occurs, which causes the pressure to rise to eleven times the initial pressure; but owing to cooling by radiation, &c., this is not reached in practice. Acetylene can be readily liquefied, having a critical temperature of 37° C. and pressure of 68

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