SCIENCE-GOSSIP. 



375 



New Minor Planets. — On March 2nd and 3rd, 

 two new pigmy planets were recorded on Professor 

 Max Wolf's photo-plates at Heidelberg. On March 

 9th Dr. J. Palisa, at Vienna, made his 83rd dis- 

 covery of a minor planet. 



Saturn's New Moon appears on four photo- 

 graphic plates exposed under the new Bruce 

 photographic doublet, 24 inches aperture, and 160 

 inches focal length. The exposures took place 

 on August 16th, 17th, and 18th, 1898, and each 

 lasted about two hours. The number of stars 

 shown, on each plate are about 100,000. The 

 plates were examined by two of them being super- 

 posed in such a manner that each star appeared 

 double. Then it was found that each plate showed 

 a minute solitary dot, whose motions were related 

 to those of the planet. By a slip of the pen, on 

 p. 333, Lowell Observatory at Flagstaff, Arizona, 

 was confounded with Harvard College Observa- 

 tory, at Cambridge, Massachusetts. The observatory 

 at Arequipa, in Peru, is connected with Harvard. 



New Star. — In examining some of the Draper 

 Memorial Photographs, Mrs. Flemming has dis- 

 discovered that on March 8th, 1898, there was a 

 new 5th magnitude star in Sagittarius, which on 

 April 29th had fallen to 10th magnitude. Its 

 spectrum showed fourteen bright lines, six of 

 which were due to hydrogen. 



CHAPTEES FOE YOUNG ASTEONOMEES. 



By Frank C. Dennett. 



CHOICE OF A TELESCOPE. 

 {Continued from, page 347.) 



The figure in the next column is that referred 

 to last month on page 347. Full particulars, with 

 prices, may be obtained from the makers, Messrs. 

 W. Banks and Co., 18, Corporation Street, Bolton. 



In advising the use of the reflector, I would 

 emphasise that the silver-on-glass Newtonian 

 pattern is intended. 



To test an achromatic telescope turn it on a 

 bright star, and remove the eyepiece. If there 

 are defects in the glass, or in the figuring, they 

 will usually show themselves in the unequal 

 illumination of the object-glass. Next put the 

 highest power eyepiece upon the instrument. 

 The star should come sharply in and out of focus. 

 In appearance it should present a tiny circular 

 disc, without wings or other appendages, except 

 one or two thin diffraction rings truly concentric 

 with the tiny disc. Sir James South once wrote : 

 "When about to buy my large object-glass ( J ) in 

 Paris, in 1829, I directed it to Aldebaran, viewed it 

 in the telescope, certainly not one minute, and 

 paid for it the next, without any one of the 

 astronomers of Paris then present, and by my 

 side, imagining I had even had the telescope on the 

 star, much less that I had purchased it in 

 consequence." 



There is one star. 5 Cygni, which is a very good 

 test of the defining power of any telescope from 

 4J to 6| inches aperture, owing to the fact that 

 its companion falls on one of the diffraction rings 

 surrounding the larger star. It is a 3rd magni- 

 tude star with an 8th magnitude companion, 

 distant l - 75", situated E.A. 19 h. 4P8 m., dec. 44° 

 53' N. These -star tests are suitable for either 

 refractors or silvered reflectors. 



(') 111 inches aperture and nearly 19 feet focal length, made 

 by Cauchoix, now mounted in the Dunsink Observatory, 

 Dublin. .■ 



Next turn the instrument upon a double star 

 nearly as close as it may be expected to divide, 

 and take note of its performance. Here is a list 

 of such objects. 

 Aper- D''s- 



Star. 



tanr.e. 



B A. 

 h. in. 



Dec. 



2 



. cl Lyrae 



.. 3-0 . 



. 18 41-0 . 



. 39.34 N 





. y Leonis 



.. 363 . 



. 10 14-4 . 



. 20.22 N 



2i . 



. . e Bootes 



.. 2-7 . 



. 14 40-6 . 



. 27.30 N 





. t 2 Lyrae 



.. 25 . 



. 18 41-1 . 



. 39.30 N 



2i'. 



. >■ Leonis 



.. 253 . 



11 18-7 . 



. 11.5 N 



2£. 



. £ Ursae Major 



.. 1-94 . 



. 11 12-9 . 



. 32.6 N 



3 . 



. 12 Lyncis 



.. 1-8 . 



. 6 37-3 . 



. 59.33 N 



o 2 . 



. a Ophiuchi 



.. 1-4 . 



. 16 25-8 . 



. 2.12 N 



4 . 



.. e Arietis 



.. 1-34 . 



. 2 535 . 



. 20.56 N 



4*. 



. 36 Andromedae 



.. 1-18 . 



. 501 . 



. 23.2 N 



5 . 



. v Orionis 



.. 1-0 . 



. 5 19-4 . 



. 2.29 S 



6* ■ 



. <" Leonis 



.. 0-84 . 



. 9 23-1 . 



. 9.30 N 



Banks' Equatorial Head and Stand. 



To test a telescope for achromatism, the moon's 

 limb, or edge, Jupiter, or Venus are best. A re- 

 flector shows no colour round the limb, but nearly 

 all achromatics do so, the blue colour being indi- 

 cative of the better objectives. It will always be 

 found, however good is the performance of a tele- 

 scope on double stars, that those of longer 

 focus will have the advantage for planetary work. 



Amongst English-made object glasses, those of 

 Cooke (Taylor's patent), Wray, and (the late) 

 T. H. Dallmeyer take the lead. M. Bardou, of 

 Paris, also sends some splendid^objectives into the 

 market. For silver-on-glass reflectors, those of 

 the late G. With, G. Calver, W. Harding and 

 Linscott may be selected with dependence. 

 (To be continued.) 



Erratum. — In the last sentence on p. 347, for 

 "0-9 inch" read "0-9"." 



