SCIENCE.

Dunstan Times, Issue 2336, 18 June 1906, Page 3

SCIENCE.

GIBRALTAR OVER-FORTIFIED.

That it Is possible to fortify a place too much is strikingly shown in the case of Gibraltar.

Ever since 1613, when it was captured by the English, sappers and miners and engineers have been hollowing oat fort after fort in the living rook to place batteries 10, until to-day tho military experts have suddenly awakened to the fact that they have undermined the rock itself with their burrowings, ana are now trying to think of some plan to strengthen it. Sj honeycombed, indeed, is it that it is estimated that if a powerful man-of-war couid get within range and get in a few shells the place would crumble away like an ant-hill 1

Whether the idea of one rather eccentric expert will be pat into praotioe—namelv, coating the whole with ateel plates after the manner of on ironclad—is not known ; but certain it ia that something will have to be done sooner or later. MOTHER EARTH’S NEW MOON. The sensational news of the discovery of tho earth's new moon has aroused keen interest among astronomers. For centuries tho idea that there might be a second moon attending the earth has been entertained by some astronomers. Various observations of circular spots seen crossing the surface of the sun, and unknown luminous planets in the sky, have been thought to lend probability to the theory that there is such a second moon attending our planet. Occasionally it has been ‘located’ by amateur astronomers. According to one such astronomer, the second moon of thp earth is very close to us, so near, in fact, that it goes around in about throe hours and twenty minutes. According to the theories, it is a groat distance from the earth.

Borne one suggested many years ago that tho reason the earth’s second moon was never seen was because it travelled round the earth at such a distance and with such speed that it kept continually on the side away from the sun, and consequently was always in the earth's shadow. Being uuiliumined by tho sunlight and having no light of its own, it would not in such a situation be visible even ns a faint star.

But if Dr Wallemath’s Iheory is true, it would appear that the earth’s fecond moon is much inure dirtant than tho moon we know. The Doctor says that the distance of tha now moon is 27-10 times greater than that of the old moon. That would make its distance 648,000 miles from the earth. Dr Waltoinaih says Lis diameter is 700 kilometres, which would ba about 440 milts. In that respect then it must very much resemble some of the larger asteroids, such as Ceres, Juno and Dallas. Compared with the larger moon its volume is as I to 123.

Its mass, ordinarily called its weight, is as Ito 80. If this is so, the relation of the masses of our two satellites is a very singular cne, as it happens to be almost precisely the same as tho relation of the earth's mass to that of the moon. That is to say, the earth weighs about eighty times as much as the moon, and according to Dr Waltemath tho old moon weighs about eighty times as much as tho new moon, which he is said to have discovered.

But it differs from the present moon in one very remarkable particular. Tho average density of tho great maou is less than that of the earth, while according th Dr Waltomath’s figures the average density of the new moon must be about tho same as the earth. In other words, while it is a very small body, it must bo heavy in proportion to its size.

In regard to the effect which euoh a body revolving around the earth (as Dr Wallemath says it does, in a period of about 177 days) would have upon oar planet, it may bo remarked that the oniy certain influence that any heavenly body has upon the earth is in the raising of tides in tho ocean, and in tho atmosphere. Now a body weighing only I-B(hh as much as the moon, and at the same time more than 2J times further away, would Eossess practically no tidal influence. The eight of tho tide which it could raise in the the ocean would be measured only by hundredths or an inch instead of several feet, as in tho case of the' old moon. Ite influence upon tho atmosphere would bo correspondingly slight. Nevertheless, a body of such a mass as Dr Waltemath says the new moon has would unquestionably affect the motion of tho old moon to a perceptible degree, and might account for tho irregularities in tho motions of the moon, which have long puzzled astronomers and which in fact were partly the cause of tho original speculations concerning the existence of a second moon.

Aa to the visibility of the alleged new moon, it may be said‘that if it were capable of reflecting the sunlight as brilliantly aa the larger moon does it ought not to bo a difficult telescopic object to see. It should appear to bo about one two-hundredth as great as tho fall moon. Allowing for its greatejiAistanco, it would then, if its surface if equafln power of reflection to that of the moon, show about one fifteen-hundroth of the Bfrht that is received from tho moon. Evidently, however, it cannot be a body as bright as that, otherwise it would be Elainly visible to astronomers and would avo been discovered long ago.