(2) This adjustment is technically called "squaring on," and is usually provided for in telescopes over 3 inches in aperture. If the optic axis of the objective does not pass through the centre of the eye-piece, the diffraction rings which are seen when the star is out of focus, will appear oval, and the focused image will be fan-shaped (p. 8). This follows from the fact that we are dealing with an oblique section of the cones of rays from the object-glass, and the rings will be most expanded and dimmest on the side which is furthest from the objectglass.

Fig. 2, a, represents the rings seen when the star is out of focus in the case of an objective seriously out of square, and Fig. 2, b, the corresponding focused image.

(3) Ordinary objectives should be so corrected that all the rays between C and F of the spectrum are brought to a common focus, these being the rays to which the

retina is most sensitive. When this is done the objective is" over-corrected," and the rays less refrangible than C are brought to a shorter focus, while those more refrangible than F are focused at a greater distance outside. Hence, supposing a white star like Vega is observed, the focused image should be surrounded by an almost imperceptible blue fringe. A little way within the focus the image should show a reddish nucleus, and outside the focus a bluish centre should be observed. The effect of the colour of the star observed must be carefully guarded against (p. 16), and an eye-piece of sufficient power should be employed, for the reason already stated.

A good method of testing for achromatism is to focus the image of a star on the slit of a spectroscope. If the image be perfectly achromatic, as in the case of a reflector, the spectrum seen will be a line of uniform thickAny departure from this will be indicated by local

ness.

widenings of the spectrum. With an ordinary objective, the spectrum should be a narrow line from C to F, widening out at each end.

(4) The absence of proper correction for spherical aberration produces very interesting features in the diffraction rings, some of which are admirably shown by the diagrams which are reproduced in Figs. 3, a, and 3, b. These represent sections of the cone of rays within and outside the focus respectively in the case of a lens in which there is positive aberration-that is, in which the rays from the outer parts of the object-glass come to a shorter focus than the central rays. In the first figure the concentration of light in the outer ring is the chief characteristic, while in the second the central ring is relatively brighter.

rapid transfer from one climate to another, would be glad to visit the island, especially if they could combine to obtain steam communication occasionally with Malta.

THE Meteorological Office of Paris has recently published its Annals for the year 1889, in three volumes, as in previous years. Volume i., under the title of Memoirs, contains a treatise by M. Fron on the course of the thunderstorms during the year, accompanied by daily charts. M. Moureaux has published the details of the magnetic observations made at Saint Maur, with a summary of the disturbances; eight plates reproduce exactly the photographic curves of the most remarkable disturbances. M. Angot gives the results of the first simultaneous observations made at the Central Meteorological Office and on the Eiffel Tower. The diurnal variation of pressure at the summit of the tower shows that the first minimum (4h.-5h. a.m.) is much more pronounced in all months at the summit than at the base, and appears to occur rather later. The first maximum (9h.10h. a.m.) is much less important at the summit, especially during the summer months, and also appears to occur later. The second minimum (2h.-3h. p.m.) is much less important at the summit, and the second maximum (about Ioh. p.m.) is rather more pronounced at the summit than at the base. The temperature of the air at the summit of the tower during the night differs constantly from that of St. Maur by less than the normal value; during the day, on the contrary, the difference of temperature is much greater between the two stations than the normal value. The wind, during all months, has a diurnal variation quite different from that at the Central Office; the maximum occurs at the middle of the night, while the minimum occurs at about 10h. a. m., and rather later in winter. Vols. ii. and iii. contain respectively the general observations and the rainfall values at the various stations.

THE idea of a "weather lexicon " has been recently developed by Herr Seemann (Met. Zeit.), using the records of the Hamburg Naval Observatory. The design is to find in a collection of daily weather charts a condition of the air over Europe resembling that of the day for which a prognosis is to be formed, and note the former sequence of weather, as throwing light on what the coming weather is likely to be. Herr Seemann uses in his lexicon all the Hamburg weather charts of the ten years 1876 to 1885. Each chart is briefly characterized; the pressure differences in three directions (north-west, south-west, and north-east from Hamburg) being indicated for each day; also wind observations in the Alps and in Norway. The days are arranged according to the amounts of difference in pressure between Hamburg and Stornoway; this gives nine groups. Under these are formed sub-groups according to the differences between Hamburg and Biarritz; and under these, others based on the differences between Hamburg and Helsingfors. The classification is further extended to wind direction. The idea seems a useful one, and experience will doubtless show in what directions the proposed method may be most advantageously modified and developed.

THE New York Nation of December 17, mentions a rather striking example of the injustice which is sometimes done to American men of science by the McKinley Tariff. A professor in one of the academies near Boston, returning from Europe, brought with him a microscope for his own use in the biological department. Under section 686 of the tariff law, which includes in the free list "professional books, implements, instru. inents, and tools of trade, occupation, or employment, in the actual possession at the time of persons arriving in the United States," he might very reasonably have expected to import this without duty, but at the steamship dock in Boston a heavy duty was demanded. He appealed to the collector, but was permitted to carry the instrument away without payment of the

tax only upon his making a gift of it to the institution with which he was connected. Even then the trouble was not quite at an end. The Principal of the Academy had to take an oath that he accepted the instrument as a free gift to the school, for its sole use, and not to be sold or given away.

IN a paper contributed to the current number of the Journal of the Franklin Institute, Mr. John Birkinbine, President of the American Institute of Mining Engineers shows that during the last thirty years the United States has increased its relative production of one ton of pig-iron for every thirty-two inhabitants to one ton of pig-iron for every seven and one-half inhabitants. The Middle States have advanced from one ton for every eleven inhabitants to one ton for every two and one-quarter inhabitants. With regard to Pennsylvania, he notes that while its population of less than 3,000,000 inhabitants in 1860 had increased to 5,250,000 in 1890, its pig-iron product of but little over 500,000 in 1860 was augmented to nearly 4,250,000 in 1890. In 1860, Pennsylvania produced one ton of pig-iron for every five inhabitants; in 1870, it made one ton of pig-iron for every three and three-quarters inhabitants; in 1880, one ton was made for every two and one-half inhabitants; and in 1890 one ton for every one and one-quarter inhabitants. Until 1692, no iron was made in Pennsylvania, and even then so little was produced that the exact locality where it was prepared is not known. As a practical producer of iron, the State's history does not begin until 1716, sixty-one years after the establishment of the industry in Massachusetts. Pigiron was not made in Pittsburg before 1859, but in thirty-one years the magnificent industry in Allegheny County advanced so steadily that in 1890 a total of 1,337,309 gross tons was produced.

MR. CHARLES R. KEYES contributes to the new instalment

of the Proceedings of the Academy of Natural Sciences, Philadelphia, a valuable paper on fossil faunas in Central Iowa. In a paper on the lower coal measures of Central Iowa, in 1888, 35 genera and nearly 60 species were mentioned. The figures are now increased to 51 and 84 respectively, and many forms have not yet been thoroughly investigated. The interest, however, lies not so much in the numerical increase of the species as in the information imparted in regard to both the geological and geographical range of the various types within and beyond the limits of the State; and in the exhibition, in many forms, of structural features which have hitherto been more or less obscure. A recent geological study of the locality has disclosed a large number of stations where animal life was at one time very prolific. Several new horizons have been definitely made out, on account of which the distribution in time of the various forms is capable of being traced with greater accuracy than has hitherto been possible.

A THIRD edition of Mr. Charles A. Cutter's "Rules for a Dictionary Catalogue," has been issued by the U.S. Bureau of Education. Mr. Cutter is librarian of the Boston Athenæum, and his experience has, of course, been of the greatest service to him in the working out of his system, which is well worthy of the attention of librarian. The objects of a "Dictionary Catalogue," as he defines them, are (1) to enable a person to find a book of which either (a) the author, (b) the title, (c) the subject, is known; (2) to show what the library has (d) by a given author, (e) on a given subject, (ƒ) in a given kind of literature; (3) to assist in the choice of a book (g) as to its edition (bibliographically), (h) as to its character (literary or topical).

PROF. E. D. COPE announces in the American Naturalist the discovery of a new species of frog in New Jersey. It is a most distinct species, and about the size of the wood frog (Rana silvatica). It is not nearly related to any species of the genus

Prof. Cope obtained five adult and two half-grown individuals, and had two other adults almost within his grasp, but they escaped him. The specimens agree nearly in size, the chief differences being observed in the amount of dark blotching of the belly and the regularity of the markings on the inferior side of the femur. The specimens were found in a "cut-off" of a tributary of the Great Egg Harbour River, in Atlantic county, New Jersey. The water is stagnant, and is well grown with Nymphæas, Utricularia, and Sphagnum. The frogs did not display any considerable powers of leaping or swimming, but concealed themselves with much ease within the aquatic vegetation. Prof. Cope did not observe any voice. In the same locality he observed the Rana virescens and clamata. The "cut-off" is in the woods, and he found no individuals in similar situations in the open country, nor any along running water in the woods. The oversight of this conspicuous species, as Prof. Cope says, is a curious circumstance.

ACCORDING to a statement in the Toronto Monetary Times, grape-culture is becoming an important industry in Ontario. The centre of the vine cultivation is between Grimsby and St. Catharines. In Essex, especially on Pelee Island, experience has shown that grapes can be profitably grown. Some local experiments show a probability that in the near future the county of Norfolk will be added to the vine land of the province. The quality of the grapes grown has of late been greatly improved, and so prolific are the vines that growers have this season in many instances had to be content to take one and a half cents a pound for good samples. Grape culture is rapidly extending, especially in the county of Welland. This year's price for grapes is perhaps about as low as they can be grown at a profit, but it looks as if the supply might in future outstrip the demand.

In the report on his work during 1890, lately issued, Mr. R. L. Jack, the Government Geologist of Queensland, refers to a collection of geological specimens forwarded by the Administrator of the Government of British New Guinea. The collection demonstrated (1) the presence of gold, topaz, and beryl in the bed of the Fly River; (2) the presence, within the drainage area of the river, of (a) stratified rocks in an unaltered condition, including sandstones, clays, limestones, and lignites; (b) metamorphosed stratified rocks, including slates and greywackes; and plutonic and igneous rocks. A number of concretionary ironstone nodules probably indicated the presence of metalliferous lodes. Some fossil corals, in limestone pebbles probably of Mesozoic age, from the first and second rapids of the Fly River, have been sent for identification to Mr. Robert Etheridge, Paleontologist to the Geological Survey of New South Wales

and the Australian Museum. A second collection of rocks from Toulon Isle, Port Hennessy, Red Point, Teste Isle, Rossel Isle, &c., was examined by Mr. Maitland. Among these were grits, sandstones, shales, limestones, basalts, granites, and quartz containing a minute quantity of gold.

M. CARTAILHAC contributes to the current number of L'Anthropologie an excellent abstract of an elaborate paper by A. J. Evans on a late Celtic urn-field at Aylesford, Kent. Other contributions are a fresh instalment of T. Volkov's interesting account of marriage rites and usages in Ukraine; a paper by E. T. Hamy on the country of the troglodytes; and an essay, also by E. T. Hamy, on the ethnographical work of Nicolas-Martin Petit.

FOR experimental proof of the principle of Archimedes, M. Paquet Journ. de Phys.) recommends the following general method: Into any vessel, V, is brought the body A (which is the object of experiment), with attached wire by which it can be conveniently hung. The vessel is then filled up with water;

then A is lifted out, leaving a vacancy equal to its volume. The vessel V is now put into one scale of a hydrostatic balance, and the body A hung under it; then weights are put into the other scale till equilibrium occurs. If now the balance is lowered till A dips wholly in the water of a lower vessel V', the disturbed equilibrium can be restored by simply filling up the vessel V with water.

IT has been long known that glass is attacked and dissolved in small quantities by ordinary water. This dissolving process Herr Pfeiffer has recently sought to prove and measure by change in the electric conductivity of the water (Ann. der Physik). He measured the increase of conductivity undergone by I cubic centimetre of pure water when it has been in contact for one hour with one square centimetre of glass surface, and concluded that the amount of glass dissolved at 20° C. was I to 2 millionths of a milligram. He found, too, that with temperature rising arithmetically, the growth of solubility is considerably more rapid than that of a geometrical series; that the increase of conductivity of the water for a given kind of glass under like conditions is a characteristic constant ; and that later, when a certain quantity of alkali is dissolved, further action involves a dissolving also of silicic acid, and the salts then formed may cause a decrease of conducting power.

December

BARON NORDENSKIÖLD communicated to the meeting of the Royal Swedish Academy of Science the fact that he has discovered notable quantities of uranium in the asphaltic or rather anthracitic minerals, accompanying the magnetic and hæmatite iron ores in Sweden. A large block of so-called "anthracite" from Norberg, for instance, leaves, when burned, ashes (13 per cent.) which contain about 6 per cent. of uranium; a similar mineral from Dannemora left, when burned, ashes containing 4 per cent. of uranium. The Norberg mineral also contains cerite and gadolinite oxides, although in small quantities, and it is remarkable that the mixture of gadolinite oxide (yttria, ytterbia, &c.) from this new provenance has the normal atomic weight of 2556 (for R2O3).

TETRA-IODIDE of carbon, CI, has been obtained in large ruby-red crystals by M. Moissan by the action of his recentlyprepared boron iodide, BI,, upon carbon tetrachloride. Boron iodide is a substance crystallizing from solution in carbon bisulphide in colourless tabular crystals which melt at 43° to a liquid boiling at 210°. It is a substance of great chemical activity, reacting with considerable energy with a large number of substances, as described in NATURE, vol. xliii. p. 568. When it is brought in contact with carbon tetrachloride, double decomposition occurs in the cold, with a large evolution of heat boron chloride and carbon tetra-iodide being formed.

4BI3 + 3CC11 = 4BCl3 + 3CI.

The best mode of operating is to heat the two substances, the crystals of boron iodide and excess of dry redistilled carbon tetrachloride, in a sealed tube for one hour at a temperature of 80°-90°. Next morning the tube is found to contain large crystals of carbon tetra-iodide, which appears to be produced in theoretical quantity. After opening the tube, the crystals are drained, washed with a solution of bisulphite of soda in order to remove the last traces of iodine, and finally dried in vacuo. When the red crystals thus obtained are heated to 100° in an exhausted sealed tube, they slowly sublime into the colder portion of the tube in magnificent brilliant red crystals very much resembling the artificial rubies prepared by MM. Fremy and Verneuil. The reactions of carbon tetra-iodide are somewhat interesting. When heated in a current of hydrogen at a temperature about 140°, it is reduced to iodoform, CHI3.

CI+H=CHI3 + HI.

When the crystals are placed in an atmosphere of chlorine they at once liquefy, and the liquid becomes hot. The products are carbon tetrachloride and liquid chloride of iodine, IC, which latter gradually volatilizes away in the form of the chloride, ICl. CI+ 4C12 = CCl4 + 4ICI.

When heated gently in dry oxygen, it becomes decomposed into iodine and carbon, which latter burns away to carbon dioxide upon slightly raising the temperature. Melted sulphur reacts with carbon tetra-iodide with considerable violence; vapour of iodine is evolved, carbon deposited, and iodide of sulphur formed. If, however, powdered sulphur is warmed with carbon tetra-iodide to 50°, iodide of sulphur and carbon bisulphide are produced. Phosphorus acts with great energy upon it, forming compounds which are still undergoing investigation. Sodium and potassium react with incandescence, an alkaline iodide and free carbon being produced. Mercury and silver likewise attack it at the ordinary temperature, and very rapidly upon warming. Warm hydrochloric and hydriodic acids attack the crystals rapidly, with formation of iodoform and liberation of vapour of iodine. A particularly interesting reaction is that with fluoride of silver. When a quantity of this salt is placed in a solution of carbon tetra-iodide in carbon tetrachloride warmed to 50°, a regular evolution of gaseous carbon tetrafluoride occurs.

CI4 + 4AgF = CF1 + 4AgI.

This reaction affords the readiest means yet discovered of preparing carbon tetrafluoride.

THE additions to the Zoological Society's Gardens during the past week include a Vervet Monkey (Cercopithecus lalandii ?) from South Africa, presented by Mr. J. Parr; a Bonnet Monkey (Macacus sinicus &) from India, presented by the Rev. W. P. Beckett; a Black-faced Kangaroo (Macropus melanops) from Australia, presented by Mr. P. Clark; two Red-crested Finches (Coryphosphingus cristatus) from South America, presented by Commander W. M. Latham, R.N., F.Z.S.

OUR ASTRONOMICAL COLUMN.

THE SECULAR VARIATION OF LATITUDES.-The American Journal of Science for December contains a paper on secular variations of latitudes, read by Prof. George C. Comstock at the Washington meeting of the American Association for the Advancement of Science. The determinations of the latitude of Greenwich made from the time of Flamsteed (1693) to nowthat is, over a period of very nearly two centuries-indicate a very appreciable progressive diminution. But as the observations were made with five different instruments, and are affected, to an uncertain extent, by various sources of error, no definite conclusion can be drawn from them. In the cases of the lati

tudes of Pulkowa, Königsberg, Washington, and Madison, however, Prof. Comstock thinks there is definite evidence of a change of latitude, and from an examination of numerous absolute observations, and a reduction of recorded star-places, he arrives at the data contained in the following table :

latitudes simultaneously determined by zenith telescope observations of the same pairs of stars. "An annual motion of the Pole of o" 045 will alter the difference of latitude of these stations by twice this amount per year, giving a change in the difference of latitude amounting to 1" in eleven years-a quantity which cannot possibly escape careful observation with the zenith telescope or prime vertical transit. If similar observations be made 20° east of Greenwich, they will furnish the best obtainable data for determining the direction of motion of the Pole." All sources of systematic error can be eliminated by the adoption of such a method, and our knowledge of secular variations of latitude, as important to the geologist as to the astronomer, will be of a more definite character than at present.

THE ROTATION OF VENUS.-Herr Löschardt sends us a paper on Schiaparelli's hypothesis as to the period of rotation of Venus, presented by him to the Vienna Academy of Sciences on March 12, 1891. He criticizes the conclusions drawn by Schiaparelli from observations made by others and himself, and points out that the observations made by Denning in 1881 favour the old rotation period of 23d. 21m. rather than one of 224 days. Herr Löschardt has made a number of drawings of the markings on the planet shown by his 3-inch refractor at Nákófalva, and the discussion of them gives support, on the whole, to Cassini's value of the rotation period. The chief reasons which led to this conclusion are the differences between Perrotin's observations and those made at Nákófalva at different hours in the same day, the circular form of polar patches, and the ellipsoidal distribution of the atmosphere, which is said to be the result of swift rotation.

STARS HAVING PECULIAR SPECTRA.—In a communication to Astronomische Nachrichten, No. 3070, Prof. Pickering records that the three stars tabulated below show bright lines in their photographic spectra, and belong to the same class as the stars discovered by Wolf and Rayet :

THE TOWER OF BABEL AND THE
CONFUSION OF TONGUES.1

WHO among the readers of ancient history has not pictured to himself great Babylon, with its long straight streets at right angles, its quays along the banks of the Euphrates, itsroyal palaces, its double walls, and last, not least, its towers in stages, dedicated to the various gods? The picture of grandeur is one of which we can form an estimate only, but it must have been magnificent beyond what was customary in those days, for had not the great Nebuchadnezzar built it? He describes at great length what he had done for the city, for its walls, for its streets, its temples, its towers, and its palaces.

But there was a time when Babylon was not the great city. At first a village settlement, it gradually arose to be the capital of a powerful State, a progress that probably occupied 4000 years, not including the pre-historical period. The story of the beginnings of this great city, which are lost in antiquity, is told in Genesis, and forms one of the most charming of the legends of the Bible. The Biblical account is given in the genealogical table just before "the generations of Shem," and seems to be an interpolation to explain the numerous languages of the world. What the source of the legend may be is uncertain, but as a whole it is unique, for though its source is possibly Babylonian, nothing like it has yet come from that country or from Assyria. The so-called Babylonian legend of the Tower of Babel seems to have nothing to do with the Biblical oneindeed, the evidence all points to its referring to something entirely different.

"As they journeyed (so the Bible narrative says) in the East, they found a plain in the land of Shinar." This land of Shinar is generally regarded as the Sumer of the Babylonian and Assyrian inscriptions. The Sumerians and Akkadians were of a different stock from the Semitic inhabitants of the country, and Abstract of a Lecture by Theo. G. Pinches, before the London Institution, December 3, 1891.