August 28, 1890] 



NATURE 



429 



Observations of Saturn at the Disappearance of 

 THE Ring. — In a memoir "Sur la variabilite des anneaux de 

 Saturne," published in the Bulletin Astronomique (vol. ii. p. 28), 

 M. E. L. Trouvelot touches on some interesting phenomena 

 that he observed in 1877-78, before, during, and after the 

 passage of the sun and earth across the plane of Saturn's rings. 

 On May 18, 1877, M. Trouvelot remarked that the illuminated 

 surface of the ring appeared notably less luminous than ihe 

 planet ; further observations confirmed this, and left no doubt 

 that its relative light diminished up to the passage of the sun 

 across its plane. It was also observed that the colour of the 

 light of the ring appeared yellowish and slightly orange when 

 compared with that of the planet, whereas observations made 

 between 1872-76 indicated that the planet was of a yellowish 

 colour when compared with the ring. The two sets of observa- 

 tions are thus diametrically opposed to each other ; and it ap- 

 pears that, when the height of the sun above the plane of the 

 ring is reduced to 4" 30', the surface of the latter gradually 

 diminishes in light with the approach of the sun to the plane, 

 and afterwards the opposite surface increases in light intensity 

 until the angular distance of the sun from the plane of the ring 

 is again 4° 30'. The cause of this diminution and increase is 

 not well known. It may be due to the change in the angle of 

 incidence of the sun's rays, and, therefore, in the amount of 

 light reflected or to the absorption of the sun's rays by the 

 atmosphere belonging to the rings, or to many other causes. 



From October 6, 1877, when the sun was 1° 49' north of the 

 plane of the rings, to February 6, 1878, when the sun crossed 

 the plane, the illuminated surface gradually decreased in width 

 until it appeared as a thin line difficult to recognize, because of 

 its extreme tenuity. It was observed that the decrease in the 

 width of the illuminated ring appeared to be produced by a 

 shadow slowly obscuring it, and M. Trouvelot attributes the 

 shadow to the existence of a zone elevated above the general 

 level of the ring and slightly inclined towards the planet. To 

 produce the observed phenomenon, a protuberant zone on the 

 ring B, and 6000 kilometres from its outer edge, would have to 

 have an elevation of about 400 kilometres above the plane of 

 the rings : that is, if the north and south surfaces are sym- 

 metrical, the thickness of the zone would be 800 kilometres. In 

 consequence, however, of the position of the zone on the ring B, 

 and 25,600 kilometres from the edge of A, the better half of it 

 is generally invisible, hence in practice the thickness may be 

 said to be 400 kilometres, or nearly 249 miles. 



Prof. A. Hall has a short note on "The Thickness of 

 Saturn's Ring," in the Astronomical journal, No. 222, and 

 develops the equation by means of which it may be deter- 

 mined. He also notes that Dusejour gives a value equivalent 

 to 958 English miles in his " Traite Analytique," t. ii. p. 127 

 (Paris, 1789), as the result of a discussion of the disappearances 

 and reappearances of the ring observed before 1789. Herschel, 

 by comparing the thickness of the ring with the apparent 

 diameters of the satellites, found the value 856 miles (Phil. 

 Trans., vol. Ixxx. pp. 6 and 7, 1790). 



Schroeter found the value of 539 English miles from measure- 

 ments of the width of the trace of the ring on the ball of the 

 planet ( " Kronographische Fragmente," pp. 157 and 21 1, Got- 

 tingen, 1808). 



W. C. and G. P. Bond by comparing the amount of light re- 

 ceived from the surface of the ring a short time before its dis- 

 appearance with the light received from the edge of the ring 

 found the value <43 miles. 



With respect to this latter value M. Trouvelot remarks: 

 " Mais Bond, qui ignorait que le systeme des anneaux de Saturne 

 n'est pas plan, et que c'est a une assez grand distance de son 

 bord exterieur qu'il atteint son maximum d'epaisseur, ne pouvait 

 arriver qu'a une evaluation erronee et trop petite de cette 

 cpaisseur." 



Several other points are touched upon in M. Trouvelot's 

 memoir, viz. that Cassini's division appeared more visible on the 

 eastern side of the planet than on the western, when the elevation 

 of the sun above the plane of the ring was between +0° 45' and 

 -f 0° 27' ; and that the edge of Saturn, like that of Jupiter, was 

 notably more luminous than other parts of the globe. The dif- 

 ference in outline between the preceding and following parts of 

 the ring, the deformation of the limb of the planet at different 

 dates, and many observations possible during the disappearance 

 of the ring are also considered. 



The memoir concludes with some remarks and suggestions on 

 the observations that should be made during 1891-92. The 



next disappearance of the ring is on September 22, 1891, and it 

 will reappear on October 30 of the same year. Again, in May 

 1892, Saturn will be well situated for observations on the 

 structure of the rings causing the shadow noticed in 1877-78. 

 It is to be hoped therefore that the increased powers now at our 

 disposal will enable many of the questions raised by M. Trouvelot 

 to be definitely settled. 



Objects having Peculiar Spectra.— In Astronomische 

 Naclirichten, No. 2986, Prof. E. C. Pickering, Director of 

 Harvard College Observatory, notes that an examination of 

 photographs taken during March and April 1890, by Mr. S. J. 

 Bailey, near Closica, Peru, has led to the discovery of some 

 interesting spectra. 



A photograph of the spectrum of R Carinse (R.A. 9h. 297m., 

 Decl. -62° 21', 1900) taken on April 4, 1890, shows that the 

 G and h lines due to hydrogen are bright, as in Mira Ceti and 

 other variables of long period. 



Two photographs taken on March 19 and 20, 1890, of the 

 star, Cordova General Catalogue, No. 15,177, magnitude 



(R.A. iih. o-8m., Decl.-65 



1900), show that it has a 



spectrum consisting mainly of bright lines, and similar to that of 

 Wolf and Rayet's three stars in Cygnus. 



The nebula, General Catalogue, No. 2581 (R.A. iih. 45'im., 

 Decl. -56° 29', 1900) has the same spectrum as General 

 Catalogue 4628. Both these objects show bright lines in the 

 ultra-violet portion of their spectra, which have not been dis- 

 covered in any other planetary nebulae. 



D.M.-f-30° 3699, magnitude 9-3 (R.A. I9h. 3i-9m., Decl. 

 -f-30° 19', 1900), is seen to have bright lines in its spectrum on 

 photographs taken at Cambridge with the 8-inch Draper tele- 

 scope on June 18, 23, and 25, 1890. The spectrum of this 

 star differs from that of other bright-line spectra of which 

 photographs have been obtained. 



NO. 1087, VOX,. 42] 



ON THE CAPTURE OF YOUNG {IMMATURE) 

 FISHES, AND WHA T CONSTITUTES AN IM- 

 MA TURK FISH. 



CINCE steam-trawling became prominent, frequent complaints 

 '"-' of the constant and great destruction of very young fishes 

 by this mode of fishing have been made ; indeed, besides the 

 injury to the so-called eggs of food-fishes — then said to be de- 

 posited on the bottom — no subject attracted more attention in 

 the Royal Commission of 1883-84 — presided over by Lord 

 Dalhousie. Recently the subject has again been urged before 

 the National Sea Fisheries Protection Association — especially 

 by the fish-merchants of London (on the alleged grounds of the 

 diminution in size of the valuable food-fishes) — and, with the 

 assistance of the Board of Trade, an International Conference, ta 

 discuss remedial measures "to be taken for the preservation and 

 development of the fisheries in the extra-territorial waters of 

 Europe," was convened in the Fishmongers' Hall. It would be 

 a misapprehension, however, to suppose that those who attended 

 the Conference confined their attention to extra-territorial waters, 

 since the inshore ground (within the three-mile limit) is really 

 more important, e.g. in regard to the preservation of certain flat 

 fishes, than the offshore. Thus, as formerly shown, the plaice 

 for the most part passes its early life in the shallow sandy bays 

 of the inshore, and as it attains a length of about fifteen inches 

 it in most cases frequents the deeper water offshore, where it 

 chiefly spawns, the pelagic ova and larvae being carried shore- 

 wards to repeat the process. In the same way multitudes of 

 small turbot, brill, and soles pass their early existence not far 

 from low-water mark on sandy beaches ; ling in the barred 

 condition amongst rocks at extreme low-water ; and cod, coal- 

 fish, pollack, and whiting, near the same regions. Remedial 

 measures therefore, applied, for instance, to the plaice in extra- 

 territorial waters, could only affect the adult or nearly adult fishes, 

 and mainly in regard to the spawning individuals, a point no 

 doubt of vital importance, but which nevertheless does not touch 

 the question before us, viz. the young or immature fishes. 



In most modes of fishing as at present followed, young or 

 immature fishes are captured. Thus, in line-fishing a consider- 

 able number are hooked throughout the year, and in certain 

 parts of the east coast many in September and October. When 

 we consider the large number of men engaged in line-fishing, and 

 the almost constant .nature of such captures, we cannot con- 

 scientiously overlook it. The drain on the young cod, haddock^ 



