August 1, 1891.] 



KNOWLEDGE. 



145 



be arrested at the first gland they reach. And this process 

 of embolism, stasis of lymph, diversion of current into 

 anastomosis, will go on until the whole of the lymphatic 

 glands, directly or indirectly connected with the vessel into 

 which the parent parasite ejects her ova, are rendered 

 impervious, provided the supply of ova is sufficient, kept 

 up long enough, or renewed from time to time. The 

 particular form of lymphatic disease, and the place 

 affected, will depend on the position occupied by the 

 parent worm, on the number of ova she ejects, on the 

 frequency with which those miscarriages are repeated, and 

 on the nature of the tissues involved, and individual 

 peculiarities and accidents." 



One great outcome of our knowledge of these Filaria? is 

 the fact that these two diseases can be prevented by 

 filtering the drinking water of the localities in which they 

 are prevalent, but the filtering should be carried out on 

 strict scientific principles. This is the more important 

 since statistics reveal to us that one in every ten Chinamen 

 is affected, and one in every twelve inhabitants of Bahia. 



LUNAR AND TERRESTRIAL VOLCANOS. 



By Rev. H. N. Hutchinson, B.A., P.G.S. 



READERS of Knowledge will not have forgotten 

 the Editor's interesting paper in the May 

 number of last year on " The Great Bright 

 Streaks which radiate from some of the larger 

 Lunar Craters." It has been suggested to me 

 that the question of the origin of these remarkable 

 streaks might be discussed from the geological point of 

 view, and that I should present some facts with regard 

 to the lines of fracture and displacement among the 

 stratified rocks of the Earth's crust which are known 

 among geologists as " faults." Geological science has 

 received valuable aid from astronomers, and possibly 

 there are questions in Astronomy on which geologists 

 might throw some light ; at all events, it is a good thing 

 occasionally that students of one science should endeavour 

 to throw light on another. I only regret that the subject 

 is not handled by one more deeply versed in lunar 

 questions. 



In my previous paper on " The Cause of Volcanic 

 Action," I mentioned the connection between volcanos, 

 mountain-chains, and lines of weakness in the Earth's 

 crust, which are closely connected with lines of fracture 

 (p. 106) ; and this would seem a fitting opportunity for 

 turning our thoughts to those remarkable outbursts of 

 volcanic action on a prodigious scale of which the Moon's 

 numerous craters stand as sUent yet speaking witnesses, 

 and to inquire how far the cracks radiating from some of 

 them may be compared with terrestrial cracks. 



In Mr. Ranyard's paper we find a summary of the 

 opinions put forward by different authorities on the 

 subject of lunar streaks. " There are certainly seven such 

 ray systems," he says, " all with craters at their centres, 

 namely : — Tycho, Copernicus, Kepler, Byrgius, Anaxagoras, 

 Aristarchus, and Gibers." Of these, Tycho is the most 

 conspicuous example ; its radiating streaks come out well 

 in lunar photographs (see tlie illustrations, pp. 1'2'J and 

 278, Vol. XIII.) The radiating streaks from Copernicus 

 are well seen in the second photo, in the December 

 number of IH'JO. Two of the longest from Tycho extend 

 to a distance of over 1000 miles from tlie crater. Nichol 

 thought, as Mr. Ranyard tell us, that they were composed 

 of matter shot up from the interior of the Moon ; and 

 compares them to mineral veins or to " trap-dykes ' (of 



basalt or other igneous rock), such as are known to pierce 

 the sedimentary strata upon Earth. 



Nasmyth's opinion was that the radiations " are cracks 

 divergent from a central region of explosion, and filled up 

 with molten matter from beneath." His experiment with 

 a glass globe to illustrate this is described in the above 

 paper (p. 130), also in Nasmyth and Carpenter's book on 

 the Moon (1874, p. 131.) "Proctor seems to have 

 favoured the trap-dyke theory. Neison, after carefully 

 setting out the observed facts, refrains from advancing any 

 theory." Young hesitates between this theory and the 

 idea that they may be mere surface markings. Mr. 

 Ranyai-d himself thinks " that they correspond to a series 

 of radiating cracks, or faults, from which comparatively 

 warm air issues charged with aqueous vapour, which is 

 deposited as hoar-frost on either side of the vent." 



Thus there seems to be a consensus of opinion that, in 

 some way or other, the radiating streaks are due to cracks, 

 and we can only conceive of such fractures as being due to 

 a disruptive action, originated by the reaction of the inte- 

 rior of the Moon upon its outer crust. Taking so much 

 for granted, we may pass on to the question of the nature 

 of the disruptive force. Was it due — as Messrs. Nasmyth 

 and Carpenter say — to the expansion of molten rocky 

 matter below the Moon's surface on nearing the point of 

 solidification ? or was it originated by the cooUng and 

 consequent contraction of the body of the Moon which 

 would leave the outer crust here and there unsupported, 

 and hence this crust in settling down and endeavouring to 

 adapt itself to a smaller surface below would undergo tan- 

 gential strains and thrusts, which, it is easy to conceive, 

 might result in a certain amount of fi-acturuig ? A simple 

 illustration of this is aft'orded by the wrinkling of the skin 

 of an apple as it dries. The soft pericarp below shrinks as 

 it loses water, and so the skin has to settle down and 

 accommodate itself to a smaller surface, and in doing so it 

 must inevitably be wrinkled, or thrown into folds. This 

 is a view which might perhaps commend itself to a geo- 

 logist, for it is on a similar theory that geologists explain 

 the great foldings which have produced terrestrial moim- 

 tain chains, which latter are clearly connected with lines 

 of weakness or fracture such as they suppose allowed 

 rocky matter from below (charged with steam) to well up 

 to the surface and so give rise to volcanic action. Vol- 

 canos, as we pointed out in our last paper, have a striking 

 connection with mountain chains. On this \dew the fold- 

 ing, contortion and fracturing of strata, so conspicuous in 

 mountains, is a secondary result of the secular refrigeration 

 of our planet. Nothing short of this seems, at present, 

 equal to the Titanic work of upheaval. At the same time 

 the theory is not proved, and some authorities refuse to 

 accept it. 



Let us now turn to the Earth and see what Geology teUs 

 us about terrestrial cracks. These are of two kinds ; first, 

 there are tlic " faults," to which we have already referred; 

 secondly, the " trap-dykes," which are very numerous in 

 Scotland and northern England. 



It may easily be conceived that the force which was 

 sufficient to raise vast masses of solid rock of immense 

 thickness ft-om the bottom of the sea, where thoy were 

 deposited, high into the air in order to form dry land, 

 and, moreover, to bend them into great folds and contor- 

 tions of all sizes, might also be sufficient to crack and 

 break them through. Accordingly we find in the stratified 

 series very frequent instances of cracks running through 

 great thicknesses of rock, and obviously caused by 

 disturbing force ; sometimes they are mere fissures, but 

 more frequently there is not only a severance but a dis- 

 placement of the rocks that have been severed. Strata 



