an autobiography-第67节
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ing by his devotion to astronomical pursuits and his profound knowledge of the subject。 He had acquired much technical skill in the construction of reflecting telescopes； and the companionship between us was thus rendered very agreeable。 There was an intimate exchange of opinions on the subject； and my friendship with him continued during forty successive years。 I was perhaps a little ahead of him in certain respects。 I had more practical knowledge of casting； for I had begun when a boy in my bedroom at Edinburgh。 In course of time I contrived many practical 〃dodges〃 （if I may use such a word）； and could nimbly vault over difficulties of a special kind which had hitherto formed a barrier in the way of amateur speculum makers when fighting their way to a home…made telescope。 I may mention that I know of no mechanical pursuit in connection with science； that offers such an opportunity for practising the technical arts； as that of constructing from first to last a complete Newtonian or Gregorian Reflecting Telescope。 Such an enterprise brings before the amateur a succession of the most interesting and instructive mechanical arts； and obliges the experimenter to exercise the faculty of delicate manipulation。 If I were asked what course of practice was the best to instil a true taste for refined mechanical work； I should say； set to and make for yourself from first to last a reflecting telescope with a metallic speculum。 Buy nothing but the raw material； and work your way to the possession of a telescope by means of your own individual labour and skill。 If you do your work with the care； intelligence； and patience that is necessary； you will find a glorious reward in the enhanced enjoyment of a night with the heavensall the result of your own ingenuity and handiwork。 It will prove a source of abundant pleasure and of infinite enjoyment for the rest of your life。
I well remember the visit I received from my dear friend Warren de la Rue in the year 1840。 I was executing some work for him with respect to a new process which he had contrived for the production of white lead。 I was then busy with the casting of my thirteen…inch speculum。 He watched my proceedings with earnest interest and most careful attention。 He told me many years after； that it was the sight of my special process of casting a sound speculum that in a manner caused him to turn his thoughts to practical astronomy； a subject in which he has exhibited such noble devotion as well as masterly skill。 Soon after his visit I had the honour of casting for him a thirteen…inch speculum； which he afterwards ground and polished by a method of his own。 He mounted it in an equatorial instrument of such surpassing excellence as enabled him； aided by his devotion and pure love of the subject； to record a series of observations and results which will hand his name down to posterity as one of the most faithful and patient of astronomical observers。
＇Image＇ Fireside； Patricroft。 After a drawing by James Nasmyth
But to return to my own little work at Patricroft。 I mounted my ten…inch home…made reflecting telescope； and began my survey of the heavens。 Need I say with what exquisite delight the harmony of their splendour filled me。 I began as a learner； and my learning grew with experience。 There were the prominent stars； the planets； the Milky Way with thousands of far…off sunsto be seen。 My observations were at first merely general； by degrees they became particular。 I was not satisfied with enjoying these sights myself； I made my friends and neighbours sharers in my pleasure； and some of them enjoyed the wonders of the heavens as much as I did。
In my early use of the telescope I had fitted the speculum into a light square tube of deal to which the eye…piece was attached； so as to have all the essential parts of the telescope combined together in the most simple and portable form。 I had often to remove it from place to place in my small garden at the side of the Bridgewater Canal； in order to get it clear of the trees and branches which intercepted some object in the heavens which I wished to see。 How eager and enthusiastic I was in those days！ Sometimes I got out of bed in the clear small hours of the morning； and went down to the garden in my night…shirt。 I would take the telescope in my arms and plant it in some suitable spot； where I might get a peep at some special planet or star then above the horizon。
It became bruited about that a ghost was seen at Patricroft！ A barge was silently gliding along the canal near midnight； when the boatman suddenly saw a figure in white。 〃It moved among the trees with a coffin in its arms！〃 The apparition was so sudden and strange that he immediately concluded that it was a ghost。 The weird sight was reported at the stations along the canal； and also at Wolverhampton； which was the boatman's headquarters。 He told the people at Patricroft on his return journey what he had seen； and great was the excitement produced。 The place was haunted： there was no doubt about it！ After all； the rumour was founded on fact； for the ghost was merely myself in my night…shirt； and the coffin was my telescope； which I was quietly shifting from one place to another in order to get a clearer sight of the heavens at midnight。
My ambition expanded。 I now resolved to construct a reflecting telescope of considerably greater power than that which I possessed。 I made one of twenty inches diameter； and mounted it on a very simple plan； thus removing many of the inconveniences and even personal risks that attend the use of such instruments。 （For illustration of the plan of mounting a large telescope； see p。 338） It had been necessary to mount steps or ladders to get at the eyepiece； especially when the objects to be observed were at a high elevation above the horizon。 I now prepared to do some special work with this instrument。 In 1842 I began my systematic researches upon the Moon。 I carefully and minutely scrutinised the marvellous details of its surface； a pursuit which I continued for many years； and still continue with ardour until 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 h
