Nov. 25, 1886] 



NA TURE 



accord with an earlier determinalion of W. Herschel's 

 (loh. i6m. 7s.), but involves a serious correction of the value 

 loh. 29m. 17s. given in most of the text-books. The error 

 probably came from a servile copying of a slip of the pen made 

 by some book-compiler, fifty years ago or more, in accidentally 

 writing Herschel's value of the rotation of the inner ring, instead 

 of that of the planet. 



Much time has been spent in observations of the rings, and 

 Trouvelot has reported a number of remarkable phenomena, 

 most of which, however, he alone has seen as yet. The most 

 recent micrometric measures have failed to confirm Struve's 

 suspicion that the rings are contracting on the planet. Extensive 

 series of observations have been made upon the satellites by 

 H. Struve, Meyer, and others in Europe, and by Hall in this 

 country. Hall's observations are especially valuable, and the 

 series is now so nearly completed that we may soon hope to 

 have most accurate tables. In the case of Hyperion, there is 

 found a singular instance of a retrograde motion of the line of 

 apsides of the orbit, produced by the action of an outside body, 

 the effect being due to the near commensurability of the periods 

 of Hyperion and Titan. This most peculiar and paradoxical 

 disturbance first showed itself as an observed fact in Hall's 

 observations ; and, soon after, Newcomb gave the mathematical 

 explanation and development. He finds the mass of Titan to 

 be about 1/12,500 that of Saturn. It maybe noted, too, that 

 Hall's observations of the motions of Mimas and Enceladus 

 indicate for the rings a mass less than i/io that deduced by 

 Bessel : instead of being l/ioo as large as the planet, they 

 cannot be more than i/iooo, and are probably less than 

 1/10,000. 



The satellites of Uranus have also been assiduously observed 

 at Washington, so that at present the Uranian system is 

 probably as accurately determined as the Jovian, perhaps more 

 so. The form of the planet has been shown to be decidedly 

 elliptical (about 1/14) by observations of Schiaparelli and at 

 Princeton ; and the same observers have detected faint belts 

 upon the disk, which have also been seen at Nice, and by the 

 Henrys in Paris. Many of the observations appear to indicate 

 a very paradoxical fact — that the belts, and consequently the 

 planet's equator, are inclined to the orbits of the satellites at a 

 considerable angle. The mathematical investigations of Tisse- 

 rand appear to demonstrate that, in the case of a planet per- 

 ceptibly flattened at the poles, satellites near enough to be free 

 from much solar disturbance must revolve nearly in the plane of 

 the equator ; while those more remote, and disturbed more by 

 the sun than by the protuberant equator of the planet, must 

 revolve nearly in the plane of the planet's orbit. Thus the two 

 satellites of Mars, the four satellites of Jupiter, and the seven 

 inner satellites of Saturn, all move nearly in the equatorial plane, 

 while our moon and Japetus move in ecliptical orbits. It is very 

 difficult to believe that the satellites of Uranus, which are cer- 

 tainly not ecliptical and are very near the planet, do not move 

 equatorially. And yet it is unquestionable that most of the 

 observations with sufficiently powerful telescopes (my own among 

 them) , do seem to indicate pretty decidedly that the planet's 

 equator is inclined as much as 15° or 20° to the orbit plane of the 

 satellites. 



As to Neptune, there is nothing new. One or two old 

 observations of the planet have turned up in the revision of old 

 star catalogues, and Hall, of Washington, has made a careful 

 and accurate determination of the orbit of its one satellite, and 

 of the planet's mass ; while Maxwell Hall, of Jamaica, has 

 deduced a very doubtful value of the planet's rotation from 

 certain photometric observations of its brightness. 



There has been some hope that a planet beyond Neptune 

 might be found. Guided by certain slight indications of sys- 

 tematic disturbances in the motion of Neptune, Todd made an 

 extended search for it in 1877-78, using the Washington tele- 

 scope, and hoping to detect it by its disk, but without results. If 

 such a planet exists, it is likely to appear as a star between the 

 nth and 13th magnitude, and may be picked up anytime by the 

 asteroid-hunters. But its slow motion, and the fact that our 

 present charts give but few stars below the 114 magnitude, will 

 lender the recognition difficult. 



The indications I h.ive spoken of, and certain others first 

 noted in 1880 by Prof G. Forbes, and depending upon the 

 behaviour of certain periodic comets, furnish pretty strong reasons 

 for believing in its existence, though as yet they fall far short of 

 making it certain. 



(To be continued.') 



A LECTURE EXPERIMENT ON THE 

 EXPANSION OF SOLIDS BY HE A T 

 T VENTURE to call attention to a simple and effective way of 

 demonstrating the linear expansion of solids when heated, 

 first suggested, I believe, by M. Kapoustine {Journal de 

 Physique, December 1883, p. 576). It answers at least as well 

 as the system of levers known as "Ferguson's pyrometer," 

 which is usually employed for the purpose, while the cost of the 

 apparatus is almost nothing, and any one can make it in ten 

 minutes. 



The principle is, to magnify the slight extension of a bar by 

 causing the end of it to roll upon a needle, and thus turn the 

 latter round and move a pointer attached to it through a sensible 

 arc. 



The figure given below will show the nature of the apparatus. 



A small flat rod of the material to be examined, such as brass, 

 iron, or glass, about 30 cm. long, i cm. broad, and 2 or 3 mm. 

 thick, is laid upon two wooden blocks, placed about 25 cm. 

 apart. A weight is put upon one end of the rod to keep it from 

 moving ; under the other end, at right angles to the length of 

 the rod, is laid a fine sewmg-needle, to the eye-end of which a 

 light pointer of straw, about 16 or 20 cm. long, is attached by 

 sealing-wax. Behind the pointer (which is painted black) a 

 screen of white cardboard is fixed on the wooden block by 

 drawing-pins. 



When the rod is heated by a lamp-flame, the free end of it, as 

 it expands, moves forward upon the needle and rolls it round, 

 its movement being shown by the motion of the pointer. Even 

 the slight expansion of a slip of glass is thus easily rendered 

 evident to a class. 



I have con-,tructed for my own use a double apparatus on the 

 same principle, in which the surfaces between which the needle 

 rolls are of brass, ground true and flat. Two bars of different 

 materials lie side by side, each having its own bit of needle and 

 aluminium pointer, ranging over the same scale. They are 

 heated equally by a broad flame (spirits of wine in a wide 

 trough) .and the difterence of expansibility as well as the fact of 

 expansion by heat is thus shown. 



It is advisable to counterpoise the pointer by putting a shot 

 or two into the lower end of the straw which projects below 

 the needle, and cementing them in by sealing-wax. Also, before 

 the experiment is shown to an audience, it is well to make sure 

 that the needle rolls fairly and freely between the bar and the 

 block. Such precautions, however, are not in the slightest 

 degree necessary for school-work ; for there is always one thing 

 wliich gives the typical boy greater pleasure than to see an 

 experiment succeed, and that is — to see it fail. 



Eton College H. G. Madan 



COMPARATIVE STUDIES UPON THE GLA- 

 CIATION OF NORTH AMERICA, GREAT 

 BRITAIN, AND IRELAND"- 

 (OBSERVATIONS extending over several years upon glacial 

 ^-^ phenomena on both sides of the Atlantic had convinced 

 the author of the essential identity of these phenomena ; and 

 the object of this paper was to show that the glacial deposits of 

 Great Britain and Ireland, like those of America, may be inter- 

 preted most satisfactorily by considering them with reference to 

 a series of great terminal moraines, which both define confluent 



* Abstract of a Paper read at the Birmingham meeting of the British 

 Association, September 1886, by Prof. H. Carvill Lewis, M.A., F.G.S. 



