SCIENCE - G 0SS1P. 



215 



appear to be real ; two others were, however, dis- 

 covered by Lassell and Otto Struve in the autumn 

 of 1847. All four of them are beyond the reach 

 .of the ordinary telescope, and they have the pecu- 

 liarity that their orbits are inclined almost at 

 right angles to the ecliptic (79°), and their motions 

 retrograde as compared with the rest of the systems 

 we have hitherto considered. The distances and 

 periods of the satellites are : — 



d. h. m. 

 Ariel .. 124,000 miles .. Period 2 12 28 

 Umbriel .. 173,000 „ .,4 3 27 



Titania .. 285,000 „ „ 8 16 55 



Oberoii .. 381,000 „ „ 13 11 6 



Before the discovery by W. Herschel in 1781 of 

 the planetary nature of Uranus the planet appears 

 to have been observed and recorded as a star no 

 less than nineteen times. 



The spectroscope shows the spectrum of Uranus 

 crossed by six broad bands, one occupying the 

 position of a hydrogen line, but the rest are not 

 known. 



Neptune. 



The story has often been told of the discovery of 

 Neptune, first on paper in England and France, 

 and then with the telescope at Berlin. In real 

 size he is believed to have a diameter of 33,011 

 miles, which means a bulk 72 times that of the 

 earth, but as his weight, bulk for bulk, is lighter 

 than any other planet except Saturn, only seven- 

 teen times the earth's mass is equal to that of 

 Neptune. The latest measures of this planet by 

 Barnard with the 40-inch Yerkes achromatic give 

 its apparent angular diameter as 2 , 436". Neptune 

 appears as a star of eighth magnitude, and even 

 with 3'7 inches aperture Webb found it dull and 

 ill defined. Some of. the descriptions given of 

 its appearance when discovered are certainly 

 exaggerated, for even with a considerable aperture 

 there is a want of sharpness about the disc, not to 

 be wondered at when one considers the small 

 amount of sunshine that reaches his surface. No 

 spots have been seen, and the spectroscope shows 

 a spectrum very like that of Uranus. In 1883 

 Maxwell Hall in Jamaica believed that he observed 

 periodical fluctuations of the planet's brightness, 

 which might possibly be owing to a rotation on its 

 axis in less than eight hours. The one satellite 

 discovered by Lassell with his 2-foot mirror on 

 October 10th, 1846, rotates, like those of Uranus, 

 in a retrograde direction. It is about 223,000 

 miles distant from its primary, has a period of 

 5 d. 21 h. 8 m., and shines as a fourteenth magnitude 

 star. Dawes saw it steadily with his 8 -inch Alvan 

 Clark object-glass, but observation of it is im- 

 possible with less powerful instruments. Lassell 

 noted that the satellite was much brighter when 

 preceding the planet than when following, making 

 it very probable that it rotates, like our moon, once 

 on its axis during one revolution. There is good 

 reason for believing that Jupiter, Saturn, Uranus, 

 and Neptune all emit some small amount of light ; 

 and it may be that in fact they are, in a small mea- 

 sure, miniature suns in the midst of their satellites. 

 From the irregularities in Neptune's movements 

 the question arises from time to time whether he 

 is the outermost planet in the solar system as he 

 travels along his mighty orbit of 8,376,000,000 

 miles in the long period of nearly 165 years, only 

 one-third of which has been completed since his 

 discovery in 1846. 



(To he continued.*) 



CONDUCTED BY B. FOULKES-WINKS, M.R.P.S. 



EXPOSURE TABLE FOR DECEMBER. 



The figures in the following table are worked out for plates ot 

 about 100 Hurter & Driffield. For plates of lower speed number 

 give more exposure in proportion. Thus plates of 50 H. & D. 

 would require just double the exposure. In the same way, 

 plates of a higher speed number will require proportionately 

 less exposure. 



Time, 11 a.m. to 1 p.m. 



Between 9 and 11 a.m. and 1 and 3 ixin. double 



the required exposure. Between 8 and 9 a.m. and 



3 and 4 p.m. multiply by 4. 



Subject 



F. 5-6 



F. 8 



F.ll 



P. 16 



F.22 

 i 



F. 32 



1 

 4- 



F.45 



F.64 



Sea and Sky. . 



ISO 



eo 



s\ 



is 



4 



1 



Open Landscape 

 and Shipping 



t* 



A 



J 



i 



4 



1 



2 



4 



Landscape.with 

 dark fore- 

 ground, Street 

 Scenes, and 



1* 



4 



1 



1 



1 



2 



4 



8 



Groups 



) 

















Portraits in 

 Rooms 



f 



16 



32 



1 



2 



4 



- 



- 



Light Interiors 



30 



1 



2 



4 



8 



16 



32 



60 



Dark Interiors 



2 



4 



8 



16 



32 



60 



120 



240 



The small figures represent seconds, large figures minutes. 

 The exposures are calculated for sunshine. If the weather is 

 cloud}', increase the exposure by half as much again ; if gloomy, 

 double the exposure. 



Exhibition of the Royal Photographic 

 Society of Great Britain. — In our last issue we 

 gave a description of the interesting display of 

 apparatus in the Fountain Court. We now pro- 

 pose to add a more detailed notice of the Pictorial 

 Section, and shall also refer to some noteworthy 

 exhibits in the Technical and Scientific Section. 

 We may at once state that it is our intention to 

 treat the whole subject from a purely photographic 

 point of view. We lay stress on this, as it would 

 appear to be the sole aim of certain exhibitors to 

 produce something as totally unlike a photograph 

 as is possible ; and these people consider this to be 

 " art." The result is arrived at by purely mechanical 

 means, and we are inclined to think often by mere 

 chance. The most simple method of studying the 

 pictures is to go round the room with the catalogue, 

 commencing at No. 1. This is quite an ordinary 

 example of a photograph of woodland scenery 

 in late autumn, by Harold W. Lane, printed in 

 platinum ; but the exhibitor has finished the picture 

 in a prettily-designed mount and frame, which pro- 

 duces a very pleasing whole. The next picture 

 that arrested our attention was No. 14, by James B. 

 Johnson, "Against the Breeze"; a charming ex- 

 ample, full of life and action. It represents a 



