160 



* KNOWLEDGE ♦ 



[Aug. 22, 1884. 



the need for a brake exists. In the event of a train 

 dividing, more especially when on either a rising or 

 a falling gradient, it is important that the brake 

 should be applied instantly to every section of the 

 train. It may be taken as a certain eventuality 

 that if a carriage gets oflF the rails, the couplings -will 

 be broken, together with the brake-pipe. The rupture 

 of this pipe, however, causes an instantaneous reduction of 

 pressure withia it to 15 lb., that is to say, to the same 

 as that of the atmosphere outside. The result is that the 

 triple valve is In-ought into energetic action, is impressed 

 downwards, and opens the small reservoir into the brake- 

 cylinder. The brake is therefore immediately and most 

 firmly applied, and the motion of the carriage arrested 

 -axitomatically. Had a device of this kind been fitted to the 

 trains which met with such fatal accidents at Downton, 

 Penistone, &c., there is every reason to believe that the 

 lives of the victims would have been spared, because the 

 carriages would have been so pulled up that they would 

 not have rushed down the embankments as they did, but 

 would in all probability have remained near the rails. 

 {To he continued.') 



OTHER WORLDS THAN OURS. 



A WEEK'S CONVERSATION ON THE PLURALITY OF 

 WORLDS. 



By Mons. de Fontenelle. 



with notes by richahd a. proctor. 



{Continued from p. 138.) 



THE SECOND EVENING.— THAT THE MOON IS A 



HABITABLE WORLD. 



NEXT morning I sent to the Marchioness's apartments, 

 to know how she had rested, and whether the 

 motion of the earth had not disturbed her t She sent word 

 back, she began to be accustomed to it, and that she had 

 slept as well or better than Copernicus himself. Soon 

 after, there came some neighbours to dinner, who, according 

 to the tiresome rural custom, staid till evening, and were 

 very obliging in going then ; for the country also gives a 

 privilege of extending their visit to the next morning, if 

 they are so disposed : when they were gone, we walk'd 

 again into the park, and immediately fell upon our systems. 

 She so well conceiv'd what I told her the night before, that 

 she desired I would proceed without any repetition. 



" Well, madam," said I, " since the sun, which is now 

 immoveable, has left off being a planet, and the earth which 

 turns round him, is now become one, you will not be sur- 

 prised when you hear that the moon is an earth too, and 

 that she is inhabited as ours is." 



" I confess," said she, " I have often heard talk of the 

 world in the moon, but I always looked upon it as visionary, 

 and mere fancy." 



" And it may be so still," said I ; "I am in this case as 

 people in a Civil war, where the uncertainty of what may 

 happen makes 'em hold intelligence with the opposite party, 

 and correspond with their very enemies : for tho' I verily 

 believe the moon is inhabited, I live civilly with those who 

 do not believe it ; and I am (like some honest gentlemen in 

 point of religion) still ready to embrace the prevailing 

 opinion : but 'till the unbelievers have a more considerable 

 advantage, I am for the people in the moon." 



" Suppose there had never been any communication 

 between Paris and St. Dennis, and a cockney who was 

 never beyond the walls of this city, saw St. Dennis from 

 the towers of Notre-Dame, you ask him if he believes St, 



Dennis is inhabited as Paris is 1 He presently answers, 

 ' No : for,' says he, ' I see people at Paris, but none at St. 

 Dermis, nor did I ever hear of any there.' 'Tis true, you 

 tell him, that from the towers of Notre-Dame he cannot 

 perceive any inhabitants at St. Dennis, because of the 

 distance ; but all that he does discover of St. Dennis, very 

 much resembles what he sees at Paris, the steeples, houses, 

 walls, (fee, so that it may very well be inhabited as Paris 

 is : all this signifies nothing, my cockney still persists that 

 St. Dennis is not inhabited, because he sees nobody there. 

 The moon is our St. Dennis, and every one of us as mere 

 cockneys as he that never was out of his own city." 



" You are too severe," said she, " upon your fellow- 

 citizens ; we are not all sure so silly as your cockney ; since 

 St. Dennis is just as Paris is, he is a fool, if he does not 

 think it inhabited : but the moon is not at all like the 

 earth." 



"Have a care what you say," replied I; "for if the 

 moon resembles the earth, you are under a necessity to 

 believe it inhabited." 



" If it be so," said she, " I own I cannot be dispensed 

 from believing it ; and you seem so confident of it, that I 

 fear I must, whether I will or no. It is true, the two 

 motions of the earth (which I could never imagine till now) 

 do a little stagger me as to all the rest. But, yet, how is 

 it possible the earth should enlighten as the moon does, 

 without which they cannot be alike t " 



" If that be all," said I, " the difference is not great, for 

 it is the sun which is the sole fountain of light : that quality 

 proceeds only from him ; and if the planets give light to us, 

 it is because they first receive it from the sun. The sun 

 sends light to the moon, and she reflects it back on the 

 earth. The earth in the same manner receives light from 

 the sun, and sends it to the moon ; for the distance is the 

 same between the earth and the moon, as between the 

 moon and the earth." 



" But is the earth," said the Marchioness, " as fit to send 

 back the light of the sun as the moon is 1 " 



" You are altogether for the moon," said I ; " she ia 

 much obliged to you. But you must know that light is 

 made up of certain little balls,* which rebound from what 

 is solid, but pass through what admits of an entrance in a 

 right line, as air or glass ; so that what makes the moon 

 enlighten us is that she is a firm and solid body, from 

 which the little balls reboimd ; and we must deny our 

 senses if we will not allow the earth the same solidity. In 

 short, the difference is how we are seated ; for the moon 

 being at so vast a distance from us, we can only discover 

 her to be a body of light, and do not perceive that she is a 

 great mass, altogether like the earth ; whereas, on the con- 

 trary, because we are so near the earth, we know her to be 

 a great mass, proper to furnish provision for animals, but 

 do not discover her to be a body of light, for want of the 

 due distance." 



"It is just so with us all," said the Lady; "we are 

 dazzled with the quality and fortune of those who are 

 above us ; when, do but look to the groundwork, and we 

 are all alike." 



" Very true," said I, " we would judge of all things, but 

 still stand in the wrong place ; we are too near to judge of 

 ourselves, and too far off to know others ; so that the true 

 way to see things as they are, is to be between the moon 

 and the earth, to be purely a spectator of this world, and 

 not an inhabitant." 



" I shall never be satisfied," said she, " for the injustice 

 we do the earth, and the too favourable opinion we have of 



* We have here a popular account of the emission theory of 

 light, which in Fontenelle's time (it is hardly necessary to say) was 

 * regarded as scarcely open to question. — R. P. 



