Oct. 14. 1875] 



NATURE 



515 



Tails of Rats and Mice 



It is, I believe, pretty generally supposed that rats and mice 

 use their tails for feeding purposes in cases where the food to be 

 eaten is contained in vessels too narrow to admit the entire body 

 of the animal. I am not aware, however, that the truth of this 

 supposition has ever been actually tested by any trustworthy 

 person, and so think that the following simple experiments are 

 worth publishing. 



Having obtained a couple of tall-shaped preserve bottles with 

 rather short and narrow necks, I filled them to within three 

 inches of the top with red currant jelly which had only half 

 stiffened. I covered the bottles with bladder in the ordinary 

 way, and then stood them in a place frequented by rats. Next 

 morning the bladder covering each of the Ijottles had a small 

 hole gnawed through it, and the level of the jelly was reduced in 

 both bottles to the same extent. Now, as this extent corre- 

 sponded to about the length of a rat's tail if inserted at the hole 

 in the bladder, and as this hole was not much more than just 

 large enough to admit the root of this organ, I do not see that 

 any further evidence is required to prove the manner in which 

 the rats obtained the jelly, viz., by repeatedly introducing their 

 tails into the^ viscid matter, and as repeatedly licking them 

 clean. 



However, to' put the question quite beyond doubt, I refilled 

 the bottles to the extent of half an inch above the jelly level left 

 by the rats, and having placed a circle of moist paper upon each 

 of the jelly surfaces, covered the bottles with bladder as before. 

 I now left the bottles in a place where there were no rats or 

 mice, until a good crop of mould had grown upon one of the 

 moistened piece; of paper. The bottle containing this crop of 

 mould I then transferred to the place where the rats were 

 numerous. Next morning the bladder had again been eaten 

 through at one edge, and upon the mould there were numerous 

 and distinct tracings of the rats' tails, resembling marks made 

 with the top of a penholder. These tracings were evidently 

 caused by the animals sweeping their tails about in the fruitless 

 endeavour to find a hole in the circle of paper which covered the 

 jelly. George J. Romanes 



Dunskaith, Ross shire 



NEWCOMB ON THE URANIA N AND 

 NEPTUNIAN SYSTEMS. 



WHEN the 26-inch equatorial, with an object-glass 

 " nearly perfect in figure," was mounted at the 

 United States Naval Observatory, Washington, it was 

 resolved that its great powers should be first devoted to 

 systematic observations of the satellites of the exterior 

 planets, with the view not only to the better determination 

 of the elements of their orbits, but, more especially, of 

 the masses of their primaries ; previous attempts in this 

 direction, from the great difficulties attending observa- 

 tions, having led to very discordant values. Accordingly 

 all the minor arrangements of the instrument were com- 

 pleted with this particular object in view, and no other 

 regular work of dissimilar character was attempted while 

 the satellite-observations were in progress. 



In the memoir (Washington Observations, 1873, Ap- 

 pendix I.) to which allusion was made in this column last 

 week, Professor Newcomb describes generally his method 

 of observation ; and with respect to his measures of the 

 inner satellites of Uranus, which he thinks may fairly be 

 regarded as the most difficult well-known objects in the 

 heavens, he expresses surprise at the degree of precision 

 with which he was able to bisect them with the faintly- 

 illuminated wire of the micrometer, an examination of 

 the individual measures having shown that they were not 

 more discordant than those of the outer satellites. 



In discussing the observations of the satellites of Ura- 

 nus, extending from January 1874 to May 1875, circular 

 elements are assumed for the formation of equations of 

 condition, and by the usual methods elliptical orbits are 

 obtained lor each satellite ; but it results that there is but 

 shght evidence of any real cxcentricity of the orbits, and 

 none whatever of any mutual inchnation. Circular ele- 

 ments derived similarly are retained, and Tables for the 

 ready prediction of the positions of the satellites which 



are most essential for their certain observation are 

 founded upon them, and appended to Prof. Newcomb's 

 memoir. The most probable mean plane of the orbits is 

 found to have the following elements : — 

 Ascending node on earth's equator ... 165° 'lo H- i°'43 (/- 1850) 

 Inchnation 75* 14 - o -14 (^-1850) 



Or, as referred to the ecliptic. 



Ascending node 1 65" -48 -H I "•40 (/— 1850) 



Inclination 97 '85 - 0013 (/- 1850) 



(The motion of the satellites of Uranus is direct upDn 

 the equator, but retrograde when referred to the ecliptic.) 

 Other elements are : — 



Radius of Period of Revo- 



orbit, lution. 



I3"78 ... 252038 



I9"20 ... 414418 



3i"-48 ... 870590 



42"io ... 13-46327 



Ariel . . 

 Umbriel 

 Titania 

 Oberon 



Mean Longitude 



2i°-83 . 



. i36°-52 . 



• 229° -93 . 



• 1 54° -83 



Mean noon at Washington, 1871, December 31, is taken 

 for the epoch of mean longitude, which is reckoned from 

 the point where the orbit intersects the plane p.-irallel to 

 the earth's equator and passing through the centre of the 

 planet. The arc values of radii of orbits are for the 

 distance [i'283[o]. If we assume the mean solar parallax, 

 8""875, and adopt Clarke's equatorial semi-diameter of the 

 earth, we find from these values the following distances 

 of the satellites from Uranus, expressed in English miles. 



Ariel 118,100 [ Titania ... 269,800 



Umbriel ... 164,550 | Oberon ... 360,800 



It may be mentioned that Sir W. Herschel's observa- 

 tions between the years 1787 and 1798 are brought to 

 bear upon the determination of the periods of Oberon 

 and Titania. 



For reasons which are given. Prof. Newcomb thinks it 

 " extremely improbable that the masses of the satellites 

 exceed Ysh^ °f ^^^^ of the planet," in which case the 

 Uranocentric perturbations due to mutual action will be 

 " incapable of detection with any instrumental means yet 

 known." He mentions that, seen with the 26-inch tele- 

 scope, the brighter satelUtes, Titania and Oberon, shine 

 with about the brilliancy of a fourth magnitude star to a 

 single unassisted eye. 



We must not omit to state that the discovery of the 

 inner satellites, Ariel and Umbriel, is distinctly assigned 

 by Prof. Newcomb to Mr. Lassell ; indeed, there appears 

 every reason for believing that these excessively minute 

 objects have not yet been recognised with any instru- 

 ments except the Washington refractor and the reflectors 

 which Mr. Lassell has constructed : the discovery of these 

 satellites may be dated from the definitive announcement 

 made by Mr. Lassell to the Royal Astronomical Society 

 in November 1851. Prof. Newcomb remarks that " where 

 any difficulty whatever is found in seeing the outer satel- 

 lites," he would not hesitate to pronounce it impossible to 

 see the inner ones, and thus it is not likely that the 

 Bothkamp and other observations can have referred to 

 the latter. 



Though no systematic search was made for additiona- 

 satellites. Prof. Newcomb believes " he may say with con- 

 siderable certainty that no satellite within 2' of the planet 

 and outside of Oberon, having one-third the brilliancy of 

 the latter, and therefore that none of Sir William 

 Herschel's supposed outer satellites can have any real 

 existence." 



In the Washington refractor the planet has always pre- 

 sented a sea-green colour, no variations of tint being ever 

 noticed. Markings upon the disc were not especially 

 looked for, but if any had been visible they would hrrdly 

 have escaped remark. 



The observations of the satellite of Neptune are treated 

 in a very similar manner to those of the satellites of 

 Uranus. No certain amount of ellipticity is exhibited, 



