SCIENTIFIC GOSSIP.

New Zealand Times, Volume XXIX, Issue 4169, 31 July 1874, Page 5

SCIENTIFIC GOSSIP.

[By (Edipua, in the Melbourne header.] The astronomical book of the season is Mr. Nasmyth’s splendid monograph, “ The Moon considered' as a Planet, a World, and a Satellite.” This is an object to the investigation of which, the author has devoted many years of his life, and in doing so has brought to bear his great mechanical skill in improving his telescope and adding to it more perfect means of observation. In the management of the illustrative photographs, which are perfect gems, considerable judgment has been displayed. Not content -with giving mere pictures of lunar features as seen from the earth, there are furnished also views of the same objects as such would look if viewed as we view an elevation on the earth, that is, in a direction at right angles to its altitude ; whilst aide by side with Tycho, or other lunar volcano, as seen from the earth, is another view showing Vesuvius as looked at from the moon. By this means the volcanic origin of lunar mountains is very clearly demonstrated since an analogy between them and their earthly prototypes is apparent at a glance. The photographs illustrating the volume are so sharp and clear that one is disposed to regard all other efforts of the same Iciud as miserable failures, and, in not a few instances, we have heard the performances in this line of the great Melbourne telescope spoken of most disparagingly as compared with Mr. Nasmyth’s marvellous productions. The reason of the sharpness is very easily explained by Mr. Nasmyth’s own statement. His illustrations are not photographs of the moon at all. He has simply, after patiently and laboriously examining the moon through the telescope, made models' of any particular mountain or crater, and then photographed the model Another advantage, besides sharpness, secured by this means is the fact that the photographer was enabled to take a view at any angle, and by throwing a strong light upon the object to secure that the shadow of lunar peaks and mountains should be projected in any wished for direction.

Those persons who have seen the moon through a telescope even of small dimensions, and especially those who have been favored by a look through the splendid instrument at the Observatory, are familiar'with the features characterising the surface of our satellite. The prineijial of these are streaks in the case of Tycho, radiating from a centre and extending for many hundred miles in length ; enormous pits, not unlike rain spots, but many miles in diameter; similar pits, circular in form, with a conical hill rising from the centre; and circular walled plains, some of which have a breadth of over 300 miles. Mr. Nasmyth explains the pits by supposing them to be craters, or rather the sort of rampart which would be formed around and at a considerable distance from the crater itself, if showers of stones and ashes were ejected through the orifice, to fall, when the projectile force was expended, by gravity upon the surface. In the oases where the central mount exists volcanic action of varying force seems to have obtained. At one period the matter thrown out was probably projected to a great height, would consequently fall at a considerable distance, and from the outer circle ; and then a time of greatly diminished activity seems to have supervened, and the ejected matter being but feebly projected, .it fell immediately around the crater, forming the central mount alluded to. The walled plains are similarly accounted for by supposing them to be large circles of the first ejected matter, filled up almost to the tops of the surrounding hills by ashes, &c., subsequently thrown out. When' the immense diameter of these ring-shaped craters and plains is considered, it seems essential that the by-gone volcanic forces acting upon the moon must have been immeasurably greater than any at present obtaining upon the earth. The present projectile force of Vesuvius, however, would have produced very different results as exercised respectively upon a large body like the earth and upon a comparatively small one such .os is the satellite. The force of gravity, in fact, upon the former is as six to one upon the latter, consequently the same explosive force would in the latter instance propel a given body to a vastly greater distance than in the former. If the theory that the moon has not and never had an atmosphere is to be maintained, the difference of the two results of volcanoes acting on the earth and moon would be increased still more, since whilst both gravity and resistance of the air would tend to diminish the initial velocity of the projectile in one case, only gravity, and that of a power one-sixth less, would tend to diminish it in the other.

The absence of a lunai' 'atmosphere is now pretty clearly established, and it is held by Mr. Nasmyth that this absence obtained also in all ages of the past, even when our satellite remained still in a molten condition. In reviewing the book Mr. Norman Lockycr, however, combats this idea, holding that it is rational to “ believe in an absolute uniformity throughout nature in such matters,” and adds, “ I do not mean uniformity of matter, so far as chemical materials go, but of manner also,” In support of the idea that the moon probably once possessed an atmosphere, it is said that that of the earth is simply a residue. We have free oxygen in the atmosphere at the present time, but the quantity must have been very much greater when the various metals now found in combination with that metalloid still existed in their pure state. This oxygen was evidently absorbed by the metals being exposed to or burnt in contact with the air, and had larger quantities of the same metals been exposed or burnt, a child can easily see that the quantity of free oxygen would be still more diminished. The eruption from volcanoes of large masses of sodium or potassium in a metallic state to absorb oxygen by contact, or of considerable volumes of hydrogen to ignite, and joining with oxygen to form water, might leave us with an atmosphere containing nothing but nitrogen, and consequently diminished by over a fifth in volume and by something more in weight, French scientific papers report that a chemist, in Fails, has succeeded in decomposing hydrogen, thus proving that it is a compound body, made up of two separate gases. One of these is said to possess considerable weight, whilst the other is much lighter than ordinary hydrogen, and is recommended for use in the inflation of balloons, which will, of course, be rendered additionally buoyant. There is nothing improbable in the story, only the advantages gained for ballooning purposes by this increased lightness are likely to be overrated. A cubic foot of hydrogen is capable of raising about an ounce, but a cubic foot of gas, the weight of which was simply nothing, would only raise a' weight equal to a similar volume of air, or the medium in which the gas might float. . The English and French coasts of the channel run for the most part into shallow water. The consequence is that the passages of harbors that may be constructed to admit large vessels at any time of the tide are speedily filled up by an accumulation of drifting shingle. M. Koumien proposes to obviate this by means which, at once bold and ingenious, also afford evidence of the wonderful engineering appliances of the present age. The projector, would build the necessary harbors in deep water, and at two or three miles out at sea, communication with the land being maintained by means of tunnels. The construction of these harbors, it is said, might ho effected in a manner similar to that adopted, to build the Plymouth breakwater, concrete blocks being placed by divers. A lighthouse placed , upon the superstructure would serve nt once as a guide to vessels and as a shaft for ventilating the tunnel. Access to the tunnel would be gained by sinking a large caisson and excavating the earth, which would help to form the outside slopes of the harbor - . Engines for driving the trains would not be used, as the weight of the carriages would enable them to run down the slope seaward, whilst as the distance would not exceed two miles they could be conveniently drawn towards the shore end by ropes and stationary engines. This method of working the trains would leave the air of the tunnel free from smoke, so that a shaft at each cud would be alone required for the purposes of ventilation. The passengers at the harbor end would bo elevated by a powerful lift. Since vessels of any size could then bo used, it is expected that a speed of sixteen miles per hour may easily bo attained, so that but little over an hour would he needed in

which to make the passage from Dover to the Drench coast, and the horrors of sea sickness, if remaining as great as ever with respect to intensity, would • nevertheless he much dimidished with regard to time. If the scheme is carried out four miles, one-fifth of the distance ■will be achieved by tunnelling, the success of the enterprise and the practical experience gained in carrying it out may go far towards showing whether the remaining distance of the channel passage may not also be traversed by a tunnel similarly constructed.