an autobiography-第76章
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til this day。 My method was as follows：
I availed myself of every favourable opportunity for carrying on the investigation。 I made careful drawings with black and white chalk on large sheets of grey…tinted paper； of such selected portions of the Moon as embodied the most characteristic and instructive features of her wonderful surface。 I was thus enabled to graphically represent the details with due fidelity as to form； as well as with regard to the striking effect of the original in its masses of light and shade。 I thus educated my eye for the special object by systematic and careful observation； and at the same time practised my hand in no less careful delineation of all that was so distinctly presented to me by the telescopeat the side of which my sheet of paper was handily fixed。 I became in a manner familiar with the vast variety of those distinct manifestations of volcanic action； which at some inconceivably remote period had produced these wonderful features and details of the moon's surface。 So far as could be observed； there was an entire absence of any agency of change； so that their formation must have remained absolutely intact since the original cosmical heat of the moon had passed rapidly into space。 The surface； with all its wondrous details； presents the same aspect as it did probably millions of ages ago。
This consideration vastly enhances the deep interest with which we look upon the moon and its volcanic details。 It is totally without an atmosphere； or of a vapour envelope； such as the earth possesses； and which must have contributed to the conservation of the cosmical heat of the latter orb。 The moon is of relatively small mass； and is consequently inferior in heat…retaining power。 It must thus have parted with its original stock of cosmical heat with such rapidity as to bring about the final termination of those surface changes which give it so peculiar an aspect。 In the case of the earth the internal heat still continues in operation； though in a vastly reduced degree of activity。 Again in the case of the moon； the total absence of water as well as atmosphere has removed from it all those denudative activities which； in the earth； have acted so powerfully in effecting changes of its surfaces as well as in the distribution of its materials。 Hence the appearance of the wonderful details of the moon's surface presents us with objects of inconceivably remote antiquity。
＇Image＇ General structure of Lunar craters。
Another striking characteristic of the moon's surface is the enormous magnitude of its volcanic crater formations。 In comparison with these； the greatest on the surface of the earth are reduced to insignificance。 Paradoxical as the statement may at first appear； the magnitude of the remains of the primitive volcanic energy in the moon is simply due to the smallness of its mass。 Being only about one…eightieth part of the bulk of the earth； the force of gravity on the moon's surface is only about one…sixth。 And as eruptive force is quite independent； as a force； of the law of gravitation； and as it acted with its full energy on matter； which in the moon is little heavier than cork； it was dispersed in divergent flight from the vent of the volcanoes； free from any atmospheric resistance； and thus secured an enormously wider dispersion of the ejected scoriae。 Hence the building up of those enormous ring…formed craters which are seen in such vast numbers on the moon's surfacesome of them being no less than a hundred miles in diameter； with which those of Etna and Vesuvius are the merest molehills in comparison。
I may mention； in passing； that the frequency of a central cone within these ring…shaped lunar craters supplies us with one of the most distinct and unquestionable evidences of the true nature and mode of the formation of volcanoes。
They are the result of the expiring energy of the volcanic discharge； which； when near its termination； not having sufficient energy to eject the matter far from its vent； becomes deposited around it； and thus builds up the central cone as a sort of monument to commemorate its expiring efforts。 In this way it recalls the exact features of our own terrestrial craters； though the latter are infinitely smaller in comparison。 When we consider how volcanoes are formed by the ejection and exudation of material from beneath the solid crust it will be seen how the lunar eminences are formed； that is； by the forcible projection of fluid molten matter through cracks or vents； through which it makes its way to the surface。
＇Image＇ Pico； an isolated Lunar Mountain 8000 feet high。
It was in reference to this very interesting subject that I made a drawing of the great isolated volcanic mountain Pico； about 8000 feet high。* ＇footnote。。。 this illustration exhibits a class of volcanic formations that may be seen on many portions of the moon's surface。 They are what I would term exudative volcanic mountains； the results of a comparatively gentle discharge of volcanic matter； which has resulted in heaped up eminences； a vast group of which were displayed in the illustration； some of them being upwards of 20；000 feet high。 。。。＇
It exhibits a very different appearance from that of our mountain ranges； which are for the most part the result of a tangential action。 In the case of the earth； the hard stratified crust had to adapt itself to the shrunken diameter of the once much hotter globe。 This tangential action is illustrated in our own persons； when age causes the body to shrink in bulk； while the skin； which does not shrink to the same extent； has to accommodate itself to the shrunken interior； and so forms wrinklesthe wrinkles of age。 This theory opens up a chapter in geology and physiology well worthy of consideration。 It may alike be seen in the structure of the surface of the earth； in an old apple； and in an old hand。* ＇footnote。。。 The shrunken hand on the other side is that of Mr。 Nasmyth； photographed by himself。 According to The Psychonomy of the Hand； by R。 Beamish； F。R。S。； author of The Life of Sir M。 I。 Brunel； it exhibits a thoroughly mechanical hand； as well as the hand of a delicate manipulator； illustrating that remarkable expression in the Book of Job； that 〃in the hand of all the sons of men God places marks； that all the sons of men may know their own works。〃ED。 。。。＇
＇Image＇ Shrunken Apple and Hand。* ＇footnote。。。 These illustrations serve to illustrate one of the most potent of geological agencies which has given the earth's surface its grandest characteristics。 I mean the elevation of mountain ranges through the contraction of the globe as a whole。 By the action of gravity the former larger surface crushes down； as it were； the contracting interior； and the superfluous matter； which belonged to a bigger globe； arranges itself by tangential displacement； and accommodates itself to the altered or decreased size of the globe。 Hence our mountain ranges； which though apparently enormous when seen near at hand are merely the wrinkles on the face of the earth。 。。。＇
While earnestly studying the details of the moon's surface； it was a source of great additional interest to me to endeavour to realise in the mind's eye the possible landscape effect of its marvellous elevations and depressions。 Here my artisic faculty came into operation。 I endeavoured to illustrate the landscape。 scenery of the Moon； in like manner as we illustrate the landscape scenery of the Earth。 The telescope revealed to me distinctly the volcanic craters； the cracks； and the ranges of mountainsby means of the light and shade on the moon's surface。 One of the most prominent conditions of the awful grandeur of lunar scenery is the brilliant light of the sun； far transcending that which we experience upon the earthenhanced by the contrast with the jet…black background of the lunar heavens； the result of the total absence of atmosphere。 One portion of the moon； on which the sun is shining； is brilliantly illuminated； while all in shade is dark。
While the disc of the sun appears a vast electric light of overpowering rayless brilliancy； every star and planet in the black vault of the lunar heavens is shining with steady brightness at all times； as；
