Gulf of Siam, when it reaches on the central line no less than 6' 50", the altitude of the sun being 8740. On its further progress, the shadow runs through Borneo, Celebes, the Islands Bouru, Amboyna, Ceram, and the Arrou Archipelago; covers completely the southern part of New Guinea, and moves then towards the New Hebrides, where the totality begins at sunset. What renders this eclipse so important an object of attention to astronomers, is the fact that the totality lasts almost as long as is possible under any circumstances. For at the commencement the Moon will have just passed a perigee of uncommon proximity, and she reaches during the eclipse the ascending node of her orbit. Thus the eclipsed sun rises nearly to the zenith of those countries where the eclipse takes place at noon; and therefore the augmentation of the moon's diameter (due to her altitude) is a maximum, and the rate at which the shadow sweeps over the surface of the earth is a minimum. The result of the coincidence of all these favourable circumstances will be an eclipse without rival in the records of past eclipses. There are to be found only two which may be compared in size with that of August 17, 1868, and none in which the totality lasts so long. The first is the eclipse of Thales (May 28, 585 B.C.), said to have been the first predicted, and to have concluded a fierce engagment between the Medes and Lydians. The second was visible on June 17, 1435, in Scotland, and the time of its occurrence was long remembered by the people of that country as "the black hour." But besides its enormous size, the eclipse deserves special attention in another respect. In researches on the nature of the red protuberances and other phenomena visible during total solar eclipses, it would certainly be of the highest importance to learn something about the nature of changes to which these appearances may be subject. On a single place upon the shadow's path, the time of visibility is too short to permit of the hope of perceiving processes of physical change in these objects; but it is far from being improbable that observations, obtained at several places along the line of totality, might afford the information we seek on this point. In the present instance the shadow touches a series of accessible regions, as we have seen. It is also very probable that favourable weather will prevail at the time of observation. It would certainly be well that efforts should speedily be made to take advantage of so favourable an occasion for extending our knowledge of solar physics. Centuries will pass before we have such another opportunity. Turning to Major Tennant's remarks on the subject of the same eclipse, we find that much has been done in the way of preparation. The Council of the Astronomical Society has decided that there should be provided for photography a silvered-glass reflector, equatorially mounted and driven by clockwork. The Astronomer Royal also offered to lend Major Tennant two telescopes from the Royal Observatory. As respects Photography, the conditions as to time rendered it unadvisable to attempt to use a speculum of more than 9 inches diameter. The picture will be taken at the side of the tube, the telescope being a Newtonian one. Provision has been made to obtain a field of more than one degree in diameter, so that, if possible, some traces of the structure of the corona may be obtained in the photograph. The important difference between the position of an equatorial used in such low latitudes as the central parts of India and one used in our latitudes, have rendered new designs necessary for almost every part of the mounting. Hence many unavoidable delays have taken place with respect to this part of the arrangements. Measures have also been taken to apply tests for the polarization of light from the coloured protuberances and the corona, the following three methods being applicable: 1st. The extinction of the polarized portion of the light by means of a Nicol's prism, reducing the intensity of the image to a minimum. 2nd. Savart's test, where parallel fringes are formed by the interference of the polarized rays, the central one being either dark or light, as its plane is in or perpendicular to the plane of polarization. 3rd. By a double-image prism and analyzing plate, giving images of complementary colours with polarized light. The first two of these tests can be instantaneously interchanged, and there is no difficulty in using all these tests successively in two minutes. For spectrum observations, the Astronomer Royal has lent Major Tennant one of the old collimators of the Transit-Circle at Greenwich Observatory. An equatorial mounting is being constructed for this, to follow any object steadily, but without clockwork. The spectroscope will allow of the spectrum being compared with a scale of equal parts, by means of which its peculiarities can be referred to the lines of the solar spectrum. All the estimates for the expenses of the proposed operations have been duly sanctioned. Mr. Proctor gives the elements of his new determination of the Rotation-period of the planet Mars. A comparison of pictures taken by Mr. Browning in February of the present year with Hooke's observations in March, 1666-giving a period of nearly two hundred and one years-have enabled Mr. Proctor slightly to correct his former estimate-in obtaining which one or two small errors had crept in. He now gives for Mars' sidereal day the period 24h. 37m. 23-73s., in place of the period 24h. 37m. 27-745s., first obtained. Mr. Cayley gives an expression for the angular distance of two planets, the sun being the centre of reference. Those who are interested in questions of this sort, will be able to judge of the nature of the paper from the statement that, and being the longitudes of the two planets in their orbits, and the longitudes of their nodes, and and their inclinations, then Mr. Cayley finds an expression for the required angular distance, in terms of cos (-), sin (v-v'), cos (+), and sin (+ v'), the coefficients involving the quantities 0, e', o, and '. Mr. Gill supplies a note on the Trapezium of Orion. He was able, with a good achromatic only 33 inches in aperture, to detect the exceedingly minute star 7 of the Trapezium. He also suspected the presence of a more minute star similar in R. A. to 9, and having the same declination as 8. It may be noticed in passing, that 6 of the Trapezium has been seen, with an achromatic only 31 inches in aperture, by Cooke. It appears that, after all, the variable T Coronæ, whose sudden appearance so startled the astronomical world in May, 1866, may have been visible before evening set in, in England, on May 12th. For Mr. Walter, surgeon of H.M.'s 4th Regiment, in North India, saw the star shining at least as brightly as Alphecca at eight o'clock on the evening of that day, an hour corresponding to about halfpast two in the afternoon at Greenwich. It seems possible therefore that Mr. Stone was mistaken in rejecting the evidence given by Mr. Barker, of Canada; evidence, however, which we are bound to say bore a very questionable appearance. Mr. Weston supplies a paper on the appearance of Jupiter's satellites and their shadows when transiting Jupiter's disc, on the evening of August 21st, 1867. He records the apparition of false satellites adjacent to the true ones, and distinct from the shadows. Such appearances, which have been observed by others, must, we think, be referred to optical delusion, since Mr. Dawes and other observers of the first class have failed to notice them. Mr. Weston, using a 9-inch Newtonian reflector, noticed that the shadow of the third satellite seemed larger than that of the fourth, an appearance which—as we have already said-seems to have been presented in almost every case, to observers who used reflecting telescopes. Mr. Leeson Prince, in a paper on the same phenomenon, calls attention to the fact that the remarkable darkness sometimes observed in the fourth satellite when transiting Jupiter's disc, was observed and recorded nearly a century-and-a-half ago by Mr. J. Pound. This well-known astronomer took the satellite for its shadow, so dark was the former; and was surprised-soon after seeing the dark spot which he thus mistook-to see another and darker shadow pass on to the planet's disc. The first, when in the middle of the disc, was almost as dark as the second when near the edge of the limb, but somewhat less in size. "From which it is very plain," he adds, "that the first of these spots was the fourth satellite itself, and the second its shadow. We have seen the first and second satellites appearing, not as dark spots, but as bright ones (somewhat differing from the light of Jupiter), for some little time after they have entered the disc; but as they approach the middle we lose sight of them; and we have frequently observed that the same satellites appeared brighter at some times than at others; and that when one of them hath shined with its utmost splendour, the light of another hath been considerably diminished. From whence it is very probable, at least, not only that the satellites revolve upon their proper axis, but also that some parts of their surfaces do very faintly-if at all-reflect the solar rays to us," an interesting passage, considering the date of the observation. 4. BOTANY AND VEGETABLE PHYSIOLOGY. Dr. Jeffries Wyman has been AMERICA.-Vibrios in Hot-water. making some experiments on the appearance in hot-water of living organisms, which have some interest as touching upon spontaneous generation and some problems of Cryptogamic Botany. He concludes 1. In thermal waters, plants belonging to the lower kinds of algæ live in water, the temperature of which, in some instances, rises as high as 208° F. 2. Solutions of organic matter boiled for twenty-five minutes, and exposed only to air which had passed through iron tubes heated to redness, became the seat of infusorial life. 3. Similar solutions contained in flasks hermetically sealed, and then immersed in boiling water for periods varying from a few minutes to four hours, also became the seat of infusorial life. The infusoria were chiefly Vibrios, Bacteriums, and Monads. 4. No ciliated infusoria, unless Monads are such, appeared in the experiments referred to in the above conclusions. 5. No infusoria of any kind appeared if the boiling was prolonged beyond a period of five hours. 6. Infusoria having the faculty of locomotion, lost this when exposed in water to a temperature of from 120° to 134° F. 7. If Vibrios, Bacteriums, and Monads are added to a clear and limpid organic solution, this becomes turbid from their multiplication in from one to two days. If, however, they have been previ ously boiled, the solution does not become turbid until from one to two days later. The experiments of Dr. Child, of Oxford, and of other recent observers, are referred to by Dr. Wyman. ENGLAND.-A new Arctic Conifer. In the 'Journal of Botany,' Mr. Andrew Murray describes the most northerly tree that has been met with on the north-west coast of America. It was found in the voyage of H.M.S. 'Herald,' forming forests on the banks of the rivers Noatak and Buckland, on the American side of Behring's Straits. This latitude is nearly seven degrees farther north than the limits of the woods on the eastern side of the American continent. This tree was described originally by Dr. Seeman as a variety of Abies alba, but Mr. Murray thinks that certain differences in the bract of the scale warrant a separation, and calls the new species Abies arctica. The desolate country where this tree is found is thus described by Dr. Seeman:-"There is nothing to relieve the monotony of the steppes. A few stunted Coniferous and Willow trees afford little variety, and even these, on passing the boundary of the frigid zone, are either transformed into dwarf bushes or disappear altogether. About Norton Sound groves of White Spruce trees and Salix speciosa are frequent; northwards they become less abundant, till in latitude 66° 44' north, on the banks of the Noatak, Pinus alba disappears." An Edible Fungus from Tahiti.-Mr. Brander, of Tahiti, gives an account of a fungus which is largely exported to Sydney. It is found principally in the Society and Leeward Islands, on decayed trees. The Tahitians call it "Teria iore" (i.e. " rat's ear"), from a fanciful resemblance of shape. The fungus first began to be collected in 1863, and fetches in China, where it is much esteemed and made into soups, from eighteen to twenty cents a pound. Excellent articles (chiefly technical) occur in the same number of the Journal of Botany,' on the Plants cultivated or naturalized in the valley of Caracas, and on the staple products of Jamaica. Weeds and their Characteristics.-Dr. Henry Trimen has made some very sensible remarks on the use of the term "weed," in reply to some observations on the same point by Dr. Seeman. Dr. Seeman says that a weed signifies a naturalized herb, which has a soft and membranaceous look, grows fast, propagates its kind with great rapidity, and spreads to the prejudice of endemic or cultivated plants, in places in some way or other disturbed by the agency Dr. Trimen urges that the popular idea of a weed is any plant, irrespective of origin or appearance, occurring in cultivated ground, in addition to, and therefore more or less interfering with and injurious to the crop intended to be grown. This is the idea of a weed in the mind of horticulturists and farmers, and as it is sufficiently definite Dr. Trimen objects to the restricted sense of man. |