lyan. 28, 1886] 



NA TURE 



303 



Large consignments of whitefish and trout ova have arrived at 

 the South Kensington Aquarium from America as a presentation 

 from the Commissioners of that country. In consequence of the 

 success attending the introduction of the first-named fish into 

 this country last year, special attention is to be given to their 

 culture during the present season with a view to their distribu- 

 tion in some of our chief lakes. The National Fish Culture 

 Association have extended their hatchery, and, in order to secure 

 healthy embryos, have adopted the new method, viz. the " under- 

 flow " system, which has been found to incubate the ova at a 

 less rale of mortality than the "overflow" system. 



Dr. S.4.MUELTENNY, the indefatigable investigator of Roman 

 antiquities on and around the Lake of Constance, has now at 

 last succeeded in laying bare the forum of the old Roman city of 

 Brigantium (Bregentz), the so-called " Rhatische Pompeii. " It 

 consists of an area on the " Oelrain " inclosed by a wall fur- 

 nished with roofed halls. There are also the remains of a 

 building with stairs and eight columns, evidently a portico of 

 imposing proportions, besides two gates leading to streets. The 

 remains are unfortunately in a very dilapidated condition, and 

 their total destruction is imminent. 



In the eleven years from 1873 to 1884 the number of lions 

 killed in Algeria was 202, for which a premium of 400/. has 

 been paid by the Government. The number of panthers 

 destroyed in the same period is 1214, and the money paid by 

 the Government 720/. About 400/. has been paid for 1882 

 hyaenas, and xdool. for 27,000 jackals. The large felidje are 

 almost extirpated principally in the western provinces, and the 

 lion of the desert is fast becoming a myth. 



In the Transactions ai the Verein fiir Erdkunde at Halle a 

 writer describes certain cave-dwellings in the province of 

 Saxony. These are occasionally found in loess formations in 

 the Balkan Peninsula (in the Lorn Palanka region, for instance), 

 but it is somewhat startling to find them used now in such a 

 cultivated place as Saxony. They are in the neighbourhood of 

 Halberstadl, quite close to the village of Langenstein. Here in 

 a sandstone hill, about a dozen caves have been dug, wliich are 

 used as dwellings. They have different rooms, light and dark, 

 as well as chimneys, windows, and doors, and are said to be 

 very dry and habitable. The writer of the account, a physician, 

 says that he found the inhabitants quite comfortable, and that 

 some of them had lived there for more than thirty years without 

 suffering from any evil effects to their health. 



We have on our table the following new books : — " Zoological 

 Record," vol. xxi. 1884 {'.'Zoological Record" Association); 

 " The Definitions of Euclid," by R. Webb (Geo. Bell and Sons) ; 

 "Organic Chemistry," by H. F. Morley (Churchill); "Ele- 

 mentary Algebra," by Chas. Smith (IVIacmillan and Co.); 

 "Eminent Naturalists," by Thos. Greenwood (Simpkin and 

 Co.). 



The additions to the Zoological Society's Gardens during the 

 past week include a Macaque Monkey {Macacui cynoinolgus) 

 from India, deposited; two White-billed Parrakeets (Tany- 

 gnaihus albirostris) from Celebes, a Bearded Lizard (Amphi- 

 bolurus barbatiu) from Australia, purchased ; a Common Otter 

 (Luira vulgaris), British, received in .exchange. 



067? ASTRONOMICAL COLUMN 

 The Density of Saturn's Ring.— M. Poincare supplies a 

 short note on the stability of Saturn's ring in the November 

 number of the Bulldin Astronomique. Laplace had shown 

 that the ring could only be stable if it were divided into several 

 concentric rings revolving at different speeds. M. Tisserand 

 had confirmed this result, and had recognised that a single ring 

 must, in order to exist, possess a much higher density than the 



planet, and had calculated the maximum breadth of each ele- 

 mentary ring in terms of its density and mean radius. M. 

 Poincare has carried this investigation a step further, and shown 

 that if the density of a ring be less than a certain amount, it 

 will, under the influence of the slightest perturbation, no longer 

 break up into a number of narrower rings, but into a great 

 number of satellites, and that if the rings be fluid and turn each as 

 a single piece, the density of the inner ring must be at least 

 1/5, and of the outer ring 1/16 that of the planet. For a ring 

 of very small satellites (not for a fluid-ring, as M. Poincare 

 erroneously states). Maxwell has shown the condition to be that 

 the density should not exceed 1/300 part of that of Saturn. 



We do not at present know the actual density of the ring 

 from observation sufficiently accurately to make therefrom any 

 certain inference as to its physical condition. Bessel's deter- 

 mination from the movement of the peri-saturnium of the orbit 

 of Titan gave the reciprocal of the mass of the ring as com- 

 pared with that of Saturn as 118, which, since the volume of 

 the ring — adopting Bond's value of 40 miles for its thickness — is 

 about 1/400 that of the planet, would make its density about 

 3 '4 times greater than the planet's. Bessel's value is, however, 

 clearly too great, as he neglected the influence of the equatorial 

 protuberance of Saturn on the movement of tlie apsides. 

 Meyer's determination of the secular variation of the line of 

 apsides of Titan, viz. dn = I726"'5, gives the reciprocal of the 

 mass of the ring as 26700, but from all the six brighter satellites 

 as i960 ; the latter value closely agreeing with Tisserand's. It 

 does not, however, seem to have been noticed that even the 

 smallest value for tlie mass considerably exceeds the highest 

 permissible in accordance with Maxwell's result, since that would 

 make the mass of the rings only 1/120,000 part of the planet's, 

 an amount we cannot hope to detect with our present resources. 



The Orbit of Tethys. — Herr Karl Bohlin has recently 

 communicated to the Swedish Academy of Sciences an interest- 

 ing discussion of the elements of the orbit of Tethys. The 

 observations discussed are those of Sir Wm. Herschel, 17891 

 reduced by Lamont, Lamont, 1836, Sir J. Herschel, 1835-7, 'h^ 

 Bonds, 1848-52, Secchi, 1856, Capt. Jacob, 1857-8, Newcomb 

 and Holden, 1S74-5, and Meyer, iSSo-i. The elements are calcu- 

 lated for each period of observation, without taking account of 

 perturbations. Herr Bohlin, then specially treating the mean 

 longitude of the epoch, and adopting i9o°'5gSi2 as the 

 value of the mean motion, draws up tables of the differences 

 between observation and calculation, and attempts to repre- 

 sent them by an empirical formula. The corrected value of the 

 mean motion is I90°'698i69, almost identical with that found 

 previously by M. Baillaud. Herr Bohlin finds that the annual 

 motion of the peri-saturnium amounts to 33°. M. Baillaud's 

 results and M. Tisserand's investigations had given the value as 

 70°. The excentricity is found as O'oo8o3 ± 0'0O077. 



The Orbit of Iapetus. — Prof. Asaph Hall has published a 

 memoir containing a very full discussion of all the observations 

 of lapetus made at Washington from the mounting of the 26- 

 inch refractor until February 29, 1S84. His finally adopted 

 elements are deduced from his own observations made between 

 June 10, 1875, and the above-mentioned date. And in deducing 

 them he has taken account of the perturbations produced by the 

 sun, lapetus being so distant from its primary that, notwith- 

 standing the distance of Saturn from the sun, these perturba- 

 tions cannot be neglected. The periodic time of the satellite 

 was found, from a comparison of Herschel's observations in 

 1789 with the conjunctions observed in 1880 and i88l, to be 

 79'33ioi52 mean solar days. The adopted mean distance de- 

 termined by two different methods of observing — one by differ- 

 ences of R. a. and declination, and the other by angles of posi- 

 tion and distances, which give very accordant results, is 

 5I5"-5I95 ± o"'02645. The corresponding reciprocal of the 

 mass of Saturn (including the planet, its ring, and its satellites) 

 is 348l'3 ± o'54, closely agreeing with that found by Meyer 

 from his observations of the six brightest satellites, viz. 

 3482-93 ± 5-50. 



A New Method of Determining the Amount of 

 Astronomical Refraction. — M. Lcewy proposes to deter- 

 mine refraction by placing a glass prism with silvered faces, 

 forming a double mirror, in front of the object-glass of an equa- 

 torial. By means of this arrangement the images of two stars — 

 one at the zenith, and the other near the horizon — can be simul- 

 taneously viewed in the field and their distance measured. This 

 distance will be affected by the maximum amount of refraction. 



