424 



NA TURE 



[March 5, 1896 



less Pheasant (P/iasianus decollaius, i ) from Northern China, a 

 Spiny-tailed Mastigure ( Uromastix acanthinurus) from Briskra, 

 Algeria, deposited ; a Rusty Urubitinga ( Uriibitinga meri- 

 dionalis) from South America, a Peregrine Falcon {Falco 

 ieregrimis), British, purchased ; a Canada Goose {Benticla 

 canadensis, $ ) from North America, received in exchange. 



OUR ASTRONOMICAL COLUMN. 



The Dimensions of Saturn. — During the oppositions of 

 1894 and 1895, Prof. Barnard made a large number of micro- 

 metric measurements of Saturn with the Lick telescope, and as 

 a result of his work he gives the following details as to the 

 dimensions of the planet (Monthly Notices, vol. Ivi. p. 163) :— 



Miles. Angle. 



Equatorial diameter of Saturn 

 Polar diameter of Saturn 

 Outer diameter of outer ring 

 Inner diameter of outer ring 

 Centre of Cassini division 

 Outer diameter of inner ring 

 Inner diameter of inner ring 

 Inner diameter of crape ring 

 Width of Cassini division 

 Diameter of Titan 



The angular measurements given above are reduced to the 

 mean distance of the planet from the sun, which is taken as 

 9-538861 astronomical units. In computing the linear dimen- 

 sions, the sun's mean distance from the earth has been taken to 

 be 92,879,000 miles. 



The value of the polar compression of the planet deduced 

 from the measures is i/i i -42. Prof. Barnard's results show a close 

 agreement with those obtained by Prof. Hall in 1884-87. The 

 mean difference between the two sets of measures is only o"-034, 

 but in the case of the outer diameter of the outer ring, Prof. 

 Barnard's measure is less by o"-34 ; it is possible that this may 

 be due to eccentricity of the outer ring. The small amount of 

 detail on the planet seen with the great telescope has given rise 

 to considerable discussion ; but observations of Jupiter and Mars 

 have convinced Prof. Barnard that the instrument is capable of 

 showing anything that can be seen in smaller telescopes, and 

 more. 



The Surface of Mars. — A preliminary note regarding his 

 observations of Mars during the opposition of 1894 is given by 

 Prof. Barnard in the paper to which reference is made in the 

 preceding note. The detail observed with the 36- inch refractor 

 was so intricate and abundant that it baffled all attempts to 

 delineate it. 



The so-called " seas" were especially rich in markings, which 

 are likened to the aspect of a mountainous country as seen from 

 a great elevation. There was no suggestion that the view was 

 one of seas and oceans, but exactly the reverse. This appear- 

 ance was especially noticed in the equatorial part of the Hour- 

 glass Sea. 



On the "continental" regions irregular features represented 

 by delicate differences of shade were noticed, but no straight 

 sharp lines were seen on these surfaces. In the region of the 

 Solis Lacus some short and rather irregular hazy lines were 

 observed, running between several of the small black spots 

 which abound there. Further details of the observations are 

 promised, and as they seem to suggest a possible change in our 

 ideas as to what represents land and water on Mars, they will 

 be looked forward to with interest. 



The Eclipsoscope. — Many attempts have been made to 

 devise a spectroscope capable of showing the whole of the sun's 

 chromosphere and prominences at a glance, but they have only 

 been partially successful, although the introduction of the 

 spectroheliograph has made it easy to register the appearances 

 photographically. Another effort to secure visual observations 

 of the entire chromosphere has been made by C. V. Zenger, 

 Director of the Prague Observatory, and with the instrument he 

 has invented— the eclipsoscope — he claims to be able to see the 

 corona as well as the chromosphere and prominences [Bull. Soc. 

 Beige d Ast. No. 1-2). A cone of crown glass or quartz is 

 symmetrically enclosed in a zinc cylinder, which is closed at the 



NO. 1375. VOL. 53] 



ends with glass plates, and the space between the cylinder and 

 cone is filled with anethol (oil of aniseed). This new form of 

 prism is equivalent to an infinite number of prisms, free from 

 prismatic aberration, and giving direct vision for the yellow rays. 

 The end of the cylinder in juxtaposition with the apex of the 

 cone is covered with a piece of tinfoil, in which a circular slit 

 2 to 3 mm. wide is cut out with the apex as its centre. A tele- 

 scope provided with a Barlow lens forms an image of the sun on 

 the slit plate, the disc being of the same size as the central disc 

 of the circular slit. Each point of the sun's limb thus gives a 

 rectilinear spectrum, and all the points together produce a cir- 

 cular spectrum, which can either be viewed with a suitable eye- 

 piece, or projected on a screen by means of a photographic lens. 

 On interposing a cell containing a solution of aniline-violet and 

 aniline-green, the red light alone is transmitted, and the chromo- 

 sphere and prominences become visible in red light. Replacing 

 this absorbing medium by another consisting of a solution of 

 chromic acid and sulphate of copper, green light is transmitted, 

 and the brightest parts of the corona are stated to become 

 visible. 



Australian Longitudes. — The whole of the existing 

 materials bearing on the subject of Australian longitudes has 

 been examined by Mr. Pietro Baracchi, in order to determine 

 the most probable values of these longitudes, which may claim 

 as their basis the full amount of evidence made known to the 

 present time. The conclusion he draws from the discussion is 

 " that the longitudes of the Australian Observatories may be 

 accepted as true only within one second of time ; and those of 

 the boundary lines of South Australia with Victoria and New 

 South Wales, within 1500 feet." 



INVESTIGA TIONS ON RONTGEN RA YS} 

 T HAVE the pleasure to communicate briefly to this Academy 

 -*- the results of some investigations I have made on the 

 Riintgen rays. 



The theoretical part of these investigations aims at determin- 

 ing whether the rays are a form of light, in the sense of being 

 vibrations in the ether ; it is known that Rontgen, in his 

 memoir, suggests that they are longitudinal waves in the ether. 

 However, on reading Rontgen's paper, I concluded from the 

 facts he had established, and more especially from the fact 

 that the rays were propagated with the same velocity in 

 different transparent media, and that a body is more trans- 

 parent the less its density, that the rays might be considered 

 as highly rarefied matter projected from the Crookes' tube, 

 matter to which lighter bodies would be more permeable. 

 Bodies would be traversed more or less easily by the small 

 particles, in the same way that a sieve more or less fine would 

 be by a stream of small shot. This suggestion I had mentioned 

 privately, and was, unknown to me, reported in a correspond- 

 ence in a political journal. 



From a short account of the conference held at Pisa, by Prof 

 Garbasso, I gathered that this idea was shared by him and the 

 well-known savant Battelli, and that their researches on the 

 subject tended to confirm it. At that time I had already made 

 experiments in the same direction. Till now all attempts to 

 discover if bodies transparent to the Rontgen rays show any 

 phenomena analogous to the different colours of ordinary light 

 have yielded negative results . Not having, however, at my 

 disposal a sufficient number of metals in thin sheets, I cannot 

 state definitely that such a colour-effect does not exist. The 

 absence of any such effect would, when more fully established, 

 certainly speak in favour of the hypothesis I suggested above — 

 that of rarefied matter projected from the tube. Of what nature 

 could this matter be ? Evidently, either ordinary matter— that 

 constituting the Crookes' tube (the glass, electrodes, or gas in the 

 tube) ; or an imponderable matter— the ether. If it were 

 ordinary matter projected /)'<?/// or through the Crookes' tube, it 

 appears probable that it could be electrified ; powerful electro- 

 static charges should then deviate the rays. I have started some 

 experiments with the view of testing this, but have encountered 

 difficulties which I shall probably be unable to overcome with 

 the few appliances at my disposal. I shall make known to the 

 Academy any results I may obtain. 



I shall now speak of my endeavours to facilitate the 

 applications of Rontgen's discovery. 



1 By Prof. E. Salvioni. Translated from the Proceedings of the Acca- 

 demia Medico-Chirurgica di Perugia, vol. viii. No. 1-2. Feb. 6, 1896, 



