Oct. 26, 1876] 



ISfATURn 



571 



sits of Mercury were observed by La Concha at Monte 

 Video, November 5, 1789 ; by Keiser at Amsterdam, 

 November 9, 1802 ; by Fisher at Lisbon, May 5, 1832 ; 

 and by Houzeau at Brussels, May 8, 1845. Taking for 

 the hehocentric longitudes of the body observed, the 

 tabular longitudes of the earth at the epochs of the obser- 

 vations, the following formula for the heliocentric longi- 

 tude {y) at any time, is obtained — 



V = 56°*04 + 4°'092307y - 7°-66 sin v — p'-iS cos v, 



where/ is the number of days from November 5, 1789. 



Then admitting the place of the node of the orbit to be 

 in 46°, a transit is indicated by the formula for November 

 9, 1848, which actually took place. 



The problem under discussion, as it refers to a possible 

 intra-Mercurial planet, is susceptible of many solutions, 

 which it becomes necessary to determine. They are 

 comprised in the formula 



V - 1390-94 + 2i4°-i8 k + {io°-9oi252 - i°-972472 k)j 

 + (-5° "3 + 5°"5 ^') cos ;'. 

 / in this case being reckoned in days from 1750*0, and k 

 being an indeterminate, which may receive values either 

 positive or negative, but necessarily whole numbers. 



\i k = o, the solution, very precise, is the one already 

 given where the duration of a revolution is 33'02 days, and 

 the semi-axis 0*20 1. 



If ^ = — I, the solution is as exact as the preceding one. 

 The revolution is 27'96 days, and the semi-axis major 

 o"i8o. 



If ^ = — 2, the solution is less exact ; the revolution 

 becomes 24*25 days less than the period of the sun's 

 rotation. 



If k .= I, a solution of the same degree of precision 

 with the last is obtained, with a revolution of 4032 days. 



And if we put k = 2, when the revolution would be 

 51*75 days, large errors will remain. 



In all these hypotheses the calculated epochs of transit 

 in 1859 (Lescarbault) and 1862 (Lummis) are very nearly 

 the same. Under these conditions M. Leverrier as- 

 sumes that we may venture on the calculation of the 

 limes of future conjunctions, which occur in the vicinity 

 of the nodes, situated in i92°*9 and 12° 9, the first point 

 being the ascending node, and with the orbit correspond- 

 ing to k = o, he determines the times of conjunction in 

 the intervals 1853-1863, 1869-1877, and 1885-1892. The 

 tables show that the epochs of transits will be regulated 

 by a period of about seventeen years, in the middle of 

 which the transits will occur, but after which none would 

 be seen for many years. Lescarbault and Lummis it 

 appears observed at the end of one series of transits, 

 which explains why in searching after them in the same 

 region of the sky observers have not seen anything, and 

 seven or eight years might elapse without more success. 

 M. Leverrier then examines the possibility of a transit of 

 the hypothetical planet in the spring of 1877. The con- 

 junction with the sun would occur on March 22 at a dis- 

 tance of io"'9 from the node, and if this distance be 

 considered certain, as well as the assumed inchnation of 

 12°, there would not be a transit, but in view of very pro- 

 bable modifications of these numbers, a transit may be 

 possible ; and he then urges observers to a close watch 

 upon the sun's disk on the 22nd of March next, seeing 

 that there would be no other transit at the spring node 

 before 1885 ; and a similar examination of the conjunc- 

 tions at the opposite node (September and October) 

 shows that for the present they do not occur under more 

 favourable conditions. The conjunction in 1876 would 

 take place on September 21, when a transit, though not 

 altogether impossible, is very doubtful. For a transit at 

 this node it is necessary, under the assumed conditions as 

 to the position of the orbit, to wait until about 1881. 



For the present, then, there remains no other resource 

 than a direct search off the sun's disk, and M. Leverrier 

 remarks that Dr. Janssen " ne ddsespere pas d'y par- 



venir, grice aux perfectionnements de I'optique cdleste, 

 auxquels il a si puissamment contribu^." The remaining 

 part of the communication to the Academy is occupied 

 with ephemerides of differences of right ascension and 

 declination of planet and sun for the last half of October. 



Mr. De la Rue has instituted a very close examination 

 of the Kew heliographs, with some interesting results. 



The Variable Stars S Cancri and U Geminorum. 

 — The following are times of visible geocentric minima 

 of S Cancri, calculated from the elements of Prof. 

 Schonfeld's latest catalogue, where the period is 

 9d. iih. 3775m.: — 



d. h. m. d. h. in. 



1876, Oct. 30 15 9 1877, Jan. 14 12 3 



Nov. 18 14 22 Feb. 2 II 18 



Dec. 7 13 35 „ 21 10 35 



,, 26 12 48 March 12 9 52 



M 31 9 9 

 While the irregularity of intervals between the observed 

 maxima of U Geminorum of late years appears to forbid 

 the hope of making a reliable prediction of these epochs 

 at present, it may assist observation of the right object 

 if it is noted that the variable precedes the principal 

 component of 2 1158, im. 26*5=., and is north of it 7' 31''. 

 The writer is infoimed by M. Otto Struve that this star 

 does not quite disappear in the Pulkowa refractor, but 

 with instruments of more ordinary dimensions it is in- 

 visible during the greater part of the period of g^ days. 

 There is a star I2*i3m. very near its position. 



BIOLOGICAL NOTES 



Cephalisation. — Such is the name given by Prof. Dana 

 to what he terms a fundamental principle in the develop- 

 ment of the system of animal life. Its meaning can be 

 best explained by the employment of the instances used 

 by its author. The lobster and the crab are closely allied 

 decapod crustaceans. In the lobster the tail is large, the 

 cephalothorax elongate, and the antennas of considerable 

 size. In the crab the tail is minute, packed under the 

 cephalo-thorax, which is short, as are the antennse ; and 

 from this we may infer that passing upwards from the 

 Macrural to the Brachyural forms there is an abbrevia- 

 tion and a compacting of structure before and behind the 

 head. " In the whale the tail is the propelling organ and 

 is of enormous power and magnitude, and the brain is 

 very small and is situated far from the head extremity in 

 a great mass of flesh and bone furnished with poor organs 

 of sense." The principle is therefore that in low types 

 " there is, usually, large size and strength behind, an 

 elongation of the whole structure, and a low degree of 

 compactness in the parts before and behind ; in the high, 

 there is a relatively shorter and more compacted struc- 

 ture, a more forward distribution of the muscular forces 

 or arrangements, and a belter head." The analogy is 

 ingenious, but we can see nothing of value in the argument 

 more than a repetition of the well-known principle that 

 height in the scale of creation and amount of cerebral 

 development are correlated phenomena. Are we to place 

 the koala, which, by the way, is wonderfully like some of 

 the much higher Lemurs in its proportions, at the top of 

 the Marsupial phyllum and the kangaroos at the bottom, 

 because the former wants the tail and has a blunt nose, 

 whilst the latter have an enormous caudal appendage and 

 a slender snout ? Is the sun-fish so much higher than the 

 eel, and the ostrich than the lyre bird 1 We fear that 

 cephalisation is not a true law of nature. 



Rhinoceroses.— Anyone visiting the Zoological Gar- 

 dens in Regent's Park at the present time can obtain ocular 

 proof of the existence of two species of single-horned rhino- 

 ceros, differing in size, texture of integument, and skin- 

 folding. On a fomier occasion (NATURE, vol. ix. p. 466) we 

 were able to demonstrate to our readers the distinguishing 

 points in the last-mentioned of these features, and in the 



