allowed to remain in the gutta percha coverings of a submarine conductor, so long will their insulation fail by slow degrees." Great improvements have of late been effected, which may be estimated by the fact that the covering of the Rangoon and Singapore cable, now in process of manufacture, insulates ten times better if reduced to the same thickness of coating than the covering of the Red Sea and India cable did before it was laid; and these marked improvements are due to the greater care used by the Gutta Percha Company, assisted by stringent electrical tests which the authors are charged by the British Government to apply. The chief characteristic of these tests is, that the conductivity of both the conducting wires and the surrounding coating, which is regarded in the light of an inferior conductor, is expressed in numerical units, capable of direct comparison. The unit of resistance adopted is that of a column of mercury, 1 metre in length and of one square millimetre sectional area, taken at the freezing-point of water (as described by Werner Siemens in Poggendorff's 'Annalen,' vol. cx.). In expressing the degrees of conductivity of both the wire and the insulating medium in definite units of resistance, not only the advantage of a more accurate comparison between the results of different indication is obtained, but subsequently, when the separate coils are united together to a single cable, it affords an admirable means of judging its electrical condition in comparing the total resistances of both the conductor and insulating medium with the sum of the resistance previously obtained in testing each coil separately; but the principal advantage derived from this system of measuring, consists in the facilities it affords in determining the position of a fault in a cable while it is being laid and after submersion. In carrying this system into practice, MM. Siemens constructed coils of definite resistance variable from 1 to 50,000 units of resistance. The cables to be tested are placed for twenty-four hours in water regulated to 75° F.; they are then removed into the testing tank of the same temperature, which is hermetically closed, and hydraulic pressure of at least 600 lbs. per square inch applied, in order to force the water into the cavities or fissures that may present themselves. It is a remarkable fact, which is also borne out by observation upon cables in process of submersion, that the application of hydrostatic pressure sensibly decreases the conductivity of gutta percha; which, however, increases again slightly beyond the former rate when the pressure is relieved. For a full description of the methods of testing employed, we must refer our readers to the paper itself. The authors give a description of a new instrument by means of which they test the inductive capacity of cables, which has also to be accurately ascertained for the purpose of detecting faults; and have affixed a Table containing many satisfactory results, and proving the correctness of a formula for calculating the specific induction of cables, which was obtained by Professor Thomson and M. Werner Siemens by different scientific deductions. The specific inductive capacity of all gutta percha is shown to be nearly the same, and to be entirely independent of the specific conductivity of the gutta percha; while India-rubber and Wray's mixture are far inferior in specific inductive capacity, being equal to 0·7 and 0.8 respectively, gutta percha being taken : = 1. In this way the cable is examined repeatedly at the earliest stages of its manufacture, in lengths of one knot, during the joining and covering of the cable, and finally during the paying out. The paper next gives a full description of the electrical tests to be applied during the paying out, and numerous formula by means of which faults in the cable are ascertained under various circumstances. By these means Messrs. Siemens were enabled to determine with great accuracy faults in the Indian cable, both during the paying out and afterwards, which enabled the contractors, Messrs. Newall and Co., to effect the necessary repairs with a certainty which could not formerly be obtained. Respecting the prospects of success of new lines of submarine cables, the paper states that, owing to the great care used, the conductor of the Rangoon and Singapore cable is fully ten times more perfectly insulated than the best cable hitherto submerged; and that it may confidently be expected that the result in practice will 1860. 3 also greatly exceed that of previous experience; still the insulating material employed remains the same, and is therefore liable to be affected by the same causes of failure. The frequent failure of gutta percha has given rise lately to several projects of substituting India-rubber and its compounds for the same, which, owing to the higher insulating properties and lesser inductive capacity of India-rubber, and above all, owing to its greater homogeneity and resisting power to effects of heat, give promise of valuable results in making electric telegraphs less liable to failure. The chief difficulty consisted hitherto in working India-rubber in such a way as to obtain uniform and perfect coatings upon the conductor without injury to the conductor itself. The authors have endeavoured to remove this difficulty in constructing a covering machine, which they brought before Section G of the Association. They conclude," We do not wish, however, to rest upon our individual efforts for the further development of this important new branch of applied science. Our object in writing this communication has been to show that, although submarine electric telegraphs have often failed, the experience gained has not been lost; and that in bringing the present stock of knowledge to bear upon the subject more complete success may be ensured." ASTRONOMY. On the Forms of certain Lunar Craters indicative of the Operation of a peculiar degrading Force. By W. R. BIRT, F.R.A.S. There are on the surface of our satellite three well-marked classes of lunar craters, those that are more or less complete in the outlines of the mountainous rings by which they are surrounded, having in many cases a somewhat deep interior, and appearing as excavations on the surface of the moon. Cleomedes, Geminus, and others in their neighbourhood are examples. We have also among the perfectly surrounded craters those that have their rings somewhat considerably elevated above the general level of the lunar surface. Tycho may be cited as the most perfect instance of the raised craters. Both these kinds agree in a very important particular; the surrounding ring (whatever may be the varying altitudes of different peaks, or however certain portions may rise higher than others) is in this class complete; there is no evidence of the operation of the peculiar degrading force, to which I shall presently allude-certainly not to any very great extent-in breaking down any portion of the surrounding annulus. A second class of lunar crater consists of those that, having the surrounding ring complete, do not exhibit the depth of such craters above specified, or the gradual rising from the general surface as seen so distinctly in Tycho; they stand out as it were above those portions of the surfaces of the moon where they occur-generally the Maria as if the smooth undulating plains had come quite up to the rings which rise abruptly from them. Most of these craters have smooth level interiors; and there are instances of the first class situated in rugged mountainous districts possessing also a smooth interior. Plato may be quoted as an example. Many instances of this class occur in which the ring is but slightly raised above the interior and exterior surfaces. The third class, to which I am particularly desirous of referring, consists of such craters as having apparently at some previous period of their history possessed a perfect ring; a degrading force, not such as may have produced the terraces and ravines which we notice in Copernicus, but something of a different character, has invaded them from without, breaking down certain portions of the annulus, and leaving only a portion of the walls standing: these craters mostly occur on the borders of the Maria; and it is not a little significant that the broken portions are invariably, so far as my observations extend, on the side next the Maria, the parts of the annuli opposite the Maria being more or less in their earlier state. The two undermentioned craters appear to be interesting examples of this classFracastorius, situated on the border of the Mare Nectaris, and Hippalus on the border of the Mare Humorum. The ring of Fracastorius is so much broken down towards the Mare Nectaris as to give the crater the appearance of a small bay, unless viewed under a suitable illumination-a very early one-when the edge of the crater towards the Mare is seen as a series of low points or peaks casting very short shadows. The floor of the interior appears to be somewhat different from the surface of the Mare, and seems to be slightly depressed below its level. The crater Hippalus is highly interesting; seen under a very early illumination: the western half of the floor is rugged, having a number of hillocks scattered over it and two minute craters; the eastern half is smooth, very like in appearance to the surfaces of the Maria; but the most remarkable feature is the line separating the crater from the Mare, just as though the Mare had come up to and swept away half the ring of the crater and a portion of its floor, the two extremities of the semicircular range of mountains being very distinct, especially the north-eastern, which terminates ab ruptly; not the vestige of a shadow is observed between the two, the light passing between them unobstructedly. On the Possibility of Studying the Earth's Internal Structure from Phenomena observed at its Surface. By Professor HENNESSY, F.R.S. This the author showed to follow as a result from the comparison of the level surface, usually called the earth's surface by astronomers and mathematicians, with the geological surface which would be presented if the earth were stripped of its fluid coating. He had made several comparisons of the arcs of meridian measured in different countries, and had been thus led to the conclusion that the surfaces in question were not only dissimilar, but that the former derived many of the irregularities which it is known to present from the influence of the obvious irregularities of the latter. In the absence of precise knowledge of the true figure of the surface of the solidified crust of the earth, as well as of the assumed level surface perpendicular to gravity, theory was necessarily somewhat in advance of observation upon this particular question. At present the number of unknown quantities involved in an inquiry as to the earth's internal structure was greater than the number of condi tions; but by knowing the true surface, and adopting the results of established physical and hydrostatical laws relative to the supposed internal fluid mass*, we should be able to form as many equations as we have unknown quantities, and thus ultimately obtain a solution. On some Recorded Observations of the Planet Venus in the Seventh Century before Christ. By the Rev. EDWARD HINCKS, D.D., of Killyleagh, Ireland. There is a tablet of baked clay in the British Museum, the inscription on which, if I interpret it aright, contains a series of observations of the planet Venus, and a series of predictions grounded on the observations. The latter are of no value; but the former may in great measure, if not altogether, determine the law by which the Assyrio-Babylonian lunar year was regulated in respect to its intercalary months. The knowledge of this law, again, will either establish or disprove the view which I have long entertained, and repeatedly expressed, that the era of Nabonassar was an astronomical, and not a political one; and I may add, it is not impossible that it may furnish a test of the genuineness of the works attributed to Quthami and other supposed ancient Babylonian writers. For these reasons I am desirous that the observations which I suppose to be recorded should be submitted to astronomers. I now offer two, which will suffice to test the correctness of my interpretation of the records. If any astronomer will take the trouble to calculate whether what is here stated to have happened would have actually happened, and will communicate the result to me, I will, if he desire it, communicate to him other records of observations, as to the interpretation of which I feel less confidence than I do as to these. I observe that the Babylonian months are expressed by monograms, for which I substitute Hebrew names of months. The Babylonian day began at noon; and that day in the evening of which the new moon was first seen was considered to be the first day of the month. I suppose, but am not very confident, that the year of the first obser* See Reports for 1859, Trans. Sect. p. 5. vation was 685. The month of Thamuz would begin in the spring. The second observation was some years later. "On the 25th of Thamuz, Venus ceased to appear in the west, was unseen for seven days, and on the 2nd of Ab was seen in the east." "On the 26th of Elul, Venus ceased to appear in the west, was unseen for eleven days, and on the 7th of the second Elul was seen in the east." This being an embolismatic year, the day last mentioned was necessarily its 184th day, and was 200 days before the first day of the new year. If, then, this day can be determined from what is recorded of Venus, the commencement of two Babylonian years out of a cycle of eight will be determined. The foregoing had been communicated to the Royal Astronomical Society, but is not yet published. Dr. Hincks now added his conviction, that by combining those observations with that of the equinox, recorded on another tablet, a translation of which was given by him in the Transactions of the Royal Irish Academy, the determination of the year in which any of those observations took place would determine the commencement of every Babylonian year. The Babylonians were acquainted with the approximate equality of eight tropical years, five synodic revolutions of Venus, and ninety-nine synodic revolutions of the moon. The first observation, if in the seventh century before Christ (which is probable, though not quite certain-later than this it could not be), must have been in a year of the form -6858 i. On the brilliant Eruption on the Sun's Surface, 1st September 1859. By R. HODGSON, F.R.A.S. While observing a group of solar spots on the 1st of September, I was suddenly surprised at the appearance of a very brilliant star of light, much brighter than the sun's surface, most dazzling to the protected eye, illuminating with its light the upper edges of the adjacent spots, not unlike in effect the edging of the clouds at sunset the rays extended in all directions, and the centre might be compared to the dazzling brilliancy of the bright star Lyræ, when seen in a large telescope with a low power. It lasted five minutes, and disappeared instantaneously about 11h 25m A.M. Telescope used an equatorial refractor, 63 inches aperture, carried by clockwork. Power single convex lens 100, with pale neutral tint sunglass. The whole aperture was used with a diagonal reflector. The phenomenon was of too short a duration to admit of a micrometrical drawing, but an eye-sketch was taken from which the enlarged diagram was made. The only other observer was Mr. Carrington at the Red Hill Observatory, but a drawing was made of the spot by the Rev. William Howlett of Hurst Green, at noon, within half an hour of the occurrence. From a photograph taken at Kew the previous day, the size (length) of the entire group appears to have been about 2 minutes 8 seconds, or say 60,000 miles. The magnetic instruments at Kew and Greenwich were simultaneously disturbed at the same instant to a considerable extent. Prospectus of the Hartwell Variable Star Atlas, with six Specimen Proofs. By JOHN LEE, LL.D. The work announced is to form one of a series of quarto volumes, of which Admiral Smyth's well-known Ædes Hartwelliana' and 'Speculum Hartwellianum' may be regarded as the commencement. It is to comprise maps of the vicinity of all stars of established variability, -at the present moment 102 in number. The light ratio or magnitude scale employed was explained, and six specimen proofs exhibited to the meeting. The scale of projection is unusually large and clear; 3 inches to one degree, to avoid crowding and confusion. After dwelling at some length upon the unsatisfactory state of our knowledge of the variable stars, and making allusion to the most recent researches and discoveries, especially to those of Professor Argelander, Sir John Herschel, Mr. Hind, and Mr. Pogson, and to the annual ephemeris of the variable stars published by the last named astronomer for four years past, Dr. Lee remarked, " A variable star usually remains unchanged for several nights, sometimes even for weeks, when either at maximum or minimum; and yet, owing to the difficulty of estimating absolute magnitudes correctly, and still more to the prevalence of haze and other uncertain atmospheric fluctuations, the most practised eye would fail to fix at all satisfactorily, either the time or amount of greatest or least brilliancy. By comparing the variable with neighbouring stars, which are of course similarly affected by atmospheric influences, most of this uncertainty is however avoided; and by careful consideration of the rapidity of increase and of decrease, the time of maximum or minimum is very closely and easily limited. In order to make such comparisons, it is requisite to know the absolute magnitudes of the stars of reference pretty correctly. A convenient number of stars in each map will therefore have the magnitudes annexed in plain figures, omitting the decimal points to prevent their being mistaken for faint stars; and it is to render this aid to future observers of variable stars that the Hartwell Atlas' is now being constructed." On the Physical Constitution of Comets. By Professor B. PIERCE, of Cambridge, United States. On the Dynamic Condition of Saturn's Rings. On the Motion of a Pendulum in a Vertical Plane when the point of suspension moves uniformly on a circumference in the same Plane. By Professor B. PIERCE, of Cambridge, United States. METEOROLOGY. On a Plan for Systematic Observations of Temperature in Mountain Several members of the Alpine Club have agreed to unite in a plan of systematic observations of temperature in the Alps, and such other mountain countries as they may visit. It is possible that the plan of combined action may eventually be extended to other objects, but for the present it embraces only such observations as may be made with thermometers. As the intention of the present paper is merely to invite the suggestions, and if possible the cooperation, of members of the Physical Section, it seems unnecessary to state in detail the arrangements which are proposed; and it will be sufficient to indicate generally the points to which it is believed that the observations about to be commenced may most usefully be directed. 1st. The condition of the upper parts of high mountains in regard to temperature is most imperfectly known. It may not be possible to learn much by direct continued observations, but it is thought that by means of self-registering instruments we may add considerably to the little which is now known. It is proposed to place such instruments, and especially minimum thermometers, on as many of the higher peaks of the Alps as possible, and to register their indications in succeeding seasons. The chief practical difficulty in carrying out this branch of the proposed plan is to find positions at great heights that are free from winter snow. It will be necessary to select vertical or nearly vertical rocks in order to attach the instruments thereto, and these are not always to be found very near to the highest summits of great mountains. 2nd. It is a matter of much interest, but of considerable difficulty, to obtain measures of the effect of the lower strata of the atmosphere upon the radiant heat of the sun. The general opinion of mountain travellers is adverse to the use of the actinometer in any of the forms in which that instrument has yet been devised, and the same may be said in regard to other instruments proposed for the same purpose. The objections to observations with the black bulb thermometers are obvious and well known instr 13 t is thought that observations made on a uniform plan, and with actly the same dimensions and construction, would give comparah would have some positive value. If it should be possible to h observations made at two stations very different in elevation, .neous, they could scarcely fail to give valuable results. vve are very ignorant at present as to the mode in which disturbances of |