July 31, 1879] 



NATURE 



319 



that a continuous brake, capable of being applied simul- 

 taneously to every wheel of a train under the conditions 

 which ha\-e been enumerated in this memorandum, is a 

 much more practical and scientific method of bringing a 

 train to rest than the old plan of concentrating the brake- 

 .power in two or three heavy brake vans placed in dif- 

 ferent parts of the train, and leaving the rest of the 

 wheels without brakes. 



The advantage which thus evidently ensues from utilis- 

 ing the adhesion of every wheel of a train for the purpose 

 of stopping a train suggests the further consideration as 

 to whether it would not be a more scientific arrangement, 

 as well as more economical in regard to the permanent 

 way of railways, to utilise the adhesion of every wheel of 

 a train for causing the train to move forward, instead of 

 depending for the moving force upon the adhesion of one 

 heavy vehicle alone, viz., the locomotive. Experiments 

 connected with the action of brakes on railway trains 

 require very delicate apparatus ; the credit of the design 

 of the apparatus used in these experiments belongs to 

 Mr. Westinghouse. The efficiency of the arrangements 

 for making the experiments is due to the London, 

 Brighton, and South Coast Railway Company, as repre- 

 sented by Mr. Knight, their general manager, who 

 afforded every facility for the use of the line, and by Mr. 

 Stroudley, the locomotive engineer of the Company. 



DOUGL.\S Galton 



OUR ASTRONOMICAL COLUMN 



^ The Comet of 1532. — This comet, the second of the 

 five observed by Apian, as described in his rare work, the 

 " Astronomicum Cffisarium," has been the subject of 

 much computation and discussion in connection with its 

 iong-assumed identity with the comet of 1661 observed 

 by Hevelius, to which attention was directed by Halley 

 when he published his " Synopsis of Cometary Astro- 

 nomy." We read: " Halley was apt to believe that the 

 comet of 1332 was the same with that observed by 

 Hevehus in the beginning of 1661, but Apian's obseiTa- 

 tions, which are the only ones we have, are too inaccu- 

 rate to determine anything certain from them in so nice 

 an affair." Pingrc fully believed in the identity of the 

 comets of 1532 and 1661, and in his " Cometographie " 

 has endeavoured to point out several previous appear- 

 ances of the same body, as in the year 1402, when he 

 expresses his conviction that the great comet recorded in 

 so many of the European chronicles about Easter was no 

 other than the one in question. Between the perihelion 

 passages of 1532 and 1661 is a period of I28;J^ years, and 

 so the return of the comet was long expected about 1789. 

 Shortly before ihis year, however, the rediscussion of the 

 observations of 1532 and 1661 was made the subject of 

 a prize by the Paris Academy of Sciences, which was 

 gained by Mechain. 



His calculations threw much doubt upon the presumed 

 identity of the comets, indeed were pretty generally con- 

 sidered as decisive against it. Olbers also recomputed 

 the orbit from the observations of 1532, and although he 

 found one much closer to that of the comet of 1661 than 

 Mechain had done, seems to have arrived at the conclu- 

 sion that the comets were not identical. Nevertheless, 

 as the year 1789 approached, sweeping-ephemerides were 

 prepared to facilitate a search, the then Astronomer- 

 Jioyal, Dr. Jilaskelyne, taking a part in this work. The 

 search was ineffectual, no one of the comets which ap- 

 peared about that year presenting any indications of 

 being the expected body. 



It is probable that the elements of the comet of 1532 

 are open to even greater uncertainty than has been 

 usually supposed. Apian's obserrations are clearly 

 affected with large errors, yet we are under the necessity 

 of relying upon them as the best data available, neither 



the vague and contradictory observations (if they deserve 

 the name) by Fracastor at Verona, nor those of Vogelin 

 at Vienna, being of service in the determination of a 

 more certain orbit than can be inferred from the observa- 

 tions in the " Astronomicum Cassarium." Apian appears to 

 have observed at Dresden, and the times of observation 

 are given by altitudes of Regulus and Arcturus ; the 

 amplitudes of the comet (S. to E.) and its altitudes are 

 recorded. The positions of the stars for iS32"o were: — 



Declination. 



Regulus 

 Arcturus 



Bight Ascension. 



,. 145 497 •■ 

 .. 20S 35-2 .. 



+ 14 I2-I 

 4-21 40'I 



Assuming Apian's station to have been in longitude 

 oh. 54m. s6s. E. and latitude 51' 3'7, his data furnish the 

 following places, which, except for the first day, do not 

 differ more than might have been expected from Pingrd's 

 reductions : — 



We subjoin an orbit depending on the observations of 

 October 2, 30, and November 7, and also Olbers' elements 

 from Hindenburg's Magazinfiir Mathematik, 1787 : — 



The comparison with the above-observed positions is 

 slightly in favour of Olbers' orbit, though this differs 

 from the place for November 7 by - 1° 40' in longitude 

 and — 4° 36' in latitude. Still it will appear that Apian's 

 observations may bo represented within their evident 

 limits of error, by orbits which differ widely. 



The Chinese observed this comet from September 2 to 

 December 25, according to the extracts from their annals 

 which have been given by E. Biot and Williams : on the 

 former date, according to Olbers' elements, the comet 

 was in longitude 98°, latitude 47° south, distant from the 

 earth 0-78, and on the latter date in longitude 249", lati- 

 tude 16° north, distant 2-13. The mention of the comet 

 having traversed Cygnus probably applies to that of 

 1533; at any rate the comet of 1532 could not have 

 passed through that constellation. 



The Sun's Parallax.— Mr. David Gill, writing from 

 Madeira, on his voyage to the Cape of Good Hope, to 

 take the direction of the Royal Observatory, as successor 

 to Mr. Stone, states in a communication to the Royal 

 Astronomical Society, that the reduction of the observa- 

 tions of Mars, made during his expedition to Ascension, 

 in 1877, have been so far completed that he is able to give 

 the resulting solar parallax. He presents values, differing 

 little inter se, deduced from various combinations of the 

 observations and, as the definite figure, 8" -78, which being 

 interpreted with the aid of Col. Clarke's last determination 

 of the earth' s equatorial semi-diameter, implies that the 

 mean distance of the earth from the sun is 93,101,000 

 miles. This is a smaller parallax than perhaps was 

 generally looked for, though not differing materially 

 from several values which have been worked out 

 recently. 



