150 



♦ KNOWLEDGE ♦ 



[Ado. 22, 1884. 



advantage. The new two-speed, central-geared Sparkbrook 

 is a well-planned and well-made machine, half spoilt by 

 being constructed on the plan I have described. The 

 Coventry Machinists have, however, introduced a new and 

 very original two-speed machine, in which speed is obtained 

 by gearing up above the size of the wheels, which is the 

 correct principle. It would be unfair for me to leave this 

 subject without saying that Messrs. Humber, Marriott, & 

 Co., Singer it Co., and Starley & Sutton, make most of 

 their mnohines with wheels from 40 in. to 44 in. diameter, 

 and gear them up according to the requirements of their 

 customers. 



A very noteworthy fact iu connection with the adoption 

 of small wheels is the wonderful performance of the various 

 safety bicycles, chiefly the Facile, the Suu and Planet, and 

 the Kangaroo. Now, these machines have wheels ranging 

 from 36 in. to 42 in. in diameter, yet their performances in 

 point of speed and of long distances will bear favourable 

 comparison with those of bicycles of the usual make, with 

 wheels from SO in. to 60 in. in diameter, though all the 

 small bicycles have to contend with additional friction in 

 extra moving parts. This is one of the most powerful, 

 because it is the most practical, argument, I have yet 

 found in favour of small wheels. 



Having now had more than a year's experience of two- 

 speed tuachines, and having three out of my five machines 

 — viz., a Sterling, a Europa, and a Rucker, provided with 

 two-speed gear, I say deliberately that I do not care in 

 future to ride any tricycle that is not furnished with two- 

 speed gearing. 



Several correspondents have called my attention to the 

 fact that while I ,have highly recommended the Sterling 

 it is only a single driver. I have not overlooked that point, 

 but I consider its merits as a most simple and efficient 

 two speed machine quite over-balance that single dis- 

 advantage. Sir John Herschel said, with regard to the 

 correct figure of a curve for the mirror of a reflecting tele- 

 scope, " that is a good curve which performs well," and I 

 say that is a good form of machine which performs well, 

 and that is the case with the Sterling. 



Some objections have been raised against two-speed 

 gearings ou the ground of their complication, the uncer- 

 tainty of their action, their liability to get out of order, 

 and the increased friction they cause. My reply is that 

 my Sterling has never, in the hundreds of reversals I 

 have given it from speed to power, failed to act instan- 

 taneously, nor has it ever given me one moment's trouble. 

 I can say the same of my Europa, so far as the speed 

 and power gearing are concerned ; and my frieud, Mr. 

 Grace, gives the same testimony as regards the Diana 

 of the same makers ; while the fact that my two-chain 

 Rucker, with speed and power gear, is by far the fastest 

 machine I have ridden, is a convincing proof that the 

 amount of extra friction produced by the second revolving 

 chain is of no material consequence, and may, in mathe- 

 matical language, be neglected. 



Very soon I propose to give Eades' new tricycle, the 

 Emperor, a trial. Thi.s novel machine has bicycle 

 .steering, and is central-geared, and is open-fronted above 

 the axle. I am prepared to find that it may require a little 

 practice to develop its best qualitie.'', and to give it, on 

 account of its novelty, the time and attention necessary to 

 form a fair opinion of its qualifications. 



The Colonial Exhiditio.v.— The Victorian Minin,? Department 

 has decided to send to the Colonial Exhibition, which is to be held 

 iu London in 188G, a scientific and economic mineral oolleotiou 

 representing the geological featiu-es of Victoria. A collection 

 which was sent to Aiii.sterd.am will be used as a nuclcns. 



THE EARTH'S SHAPE AND MOTIONS. 



By Richard A Proctor. 



( Continued from page 134.) 

 CHAPTER ir.— THE DIURNAL MOTION OF THE STARS.* 



HAVING satisfitd himself respecting the character of 

 the sun's diurnal motion, our observer, we will sup- 

 pose, turns his attention to the celestial objects which make 

 their appearance when the sun is below the horizon. 



Among these the moon is the first to attract his attention. 

 I do not propose, however, at present, to devote much space 

 to the diurnal motion of the moon, which closely resembles 

 that of the sun. It may be followed with the instrument 

 represented by Fig. 5, p. 133, without any change what- 

 ever, either in the position of the instrument or in its con- 

 struction. The only peculiarity which would be noticed 

 would be, that the rate of the moon's motion, though 

 uniform, is not e.xactly the same as that of the sun's motion, 

 but somewhat slower. 



The stars which seem scattered over the whole sky in 

 unnumbered profusion, are the objects to which our observer 

 is now supposed to turn his attention. 



A very short time suSices to show that, in the east, stars 

 are rising into view, while in the west stars are setting. 

 INIore careful observation shows that all the stars visible to 

 tlie eye are moving with greater or less speed. The stars 

 which rise in the east pass over to the south, where they 

 attain their greatest elevation ; and their motion con- 

 tinuing, they pass down to the west, where they set. Stars 

 which rise towards the south of east attain but a small 

 elevation when due south, and set towards the south-west. 

 Stars which rise towards the north of east attain a con- 

 siderable elevation when due south, and set towards the 

 north of west Other stars are seen, which neither rise 

 nor set ; but appear to travel in circles around a point on 

 the northern skies. And stars very near that point seem 

 scarcely to move at all. 



Such are the general features of the stellar diurnal 

 motions ; but our observer is now to inquire what are the 

 exact paths which the stars appear to follow. 



He might notice that a star rising in the east attains in 

 the south about the same elevation as the sun when that 

 luminary rises due east. He is led, therefore, to inquire 

 whether the whole system of the stars maj- not be re- 

 volving (really, or in appearance,) after precisely the same 

 law as he had observed in the case of the sun. The instru- 

 ment which he has constructed to follow the solar diurnal 

 motion (Chapter I., Fig. 5) will serve equally well to 

 follow the sidereal motion, if this sui^picion be correct ; 

 only the observer must be able to look along the rod L M 

 at a star. He need not, however, remove the circular card 

 at M. He may bore a hole through it, and place another 

 card similarly pierced at the end L of the rod, so that the 

 two holes may be directly opposite each other. It, how- 

 ever, the rod L M is a tube, he can look yet more con- 

 veniently at a star through this tube. 



Thus provided, the observer directs L M to any star 

 whatever, noticing what division of the card H falls opposite 

 the opening in the upright B. At the end of half-an-hour 

 (say) he again directs the tube towards the star. He finds 

 that 1 1 do this he has only to turn the rod F G round on 

 its axis, just as he had done in the case of the sun, and 

 apparently through exactly the same angle. In reality the 

 angle is slightly greater, a matter which will presently be 

 noticed more at length. But the great point to be here 



* The word diurnal in astronomy is not used as the converse of the 

 word nocturnal, but is applicable to any motions observed dnrinp 

 the twenty-four hours, from noon of one day to noon of the next. 



