74 



Notices respecting New Books. 



a periodic time of 513 years. It is, however, to be remarked that 

 after the date (1832) of that communication, the stars went through 

 a critical part of their relative orbit, and subsequent observations 

 were more suited to an exact determination of the periodic time. 

 Sir John Herschel afterwards stated the period to be short of 150 

 years. Madler found 145 years, Henderson, 143. Finally, in the 

 volume of the Cape observations. Sir John Herschel entered upon are- 

 investigation of the orbit, and concludes the research with the following 

 summary : — " Comparing the orbits which seem entitled to most 

 reliance, it appears certain that the eccentricity lies between 0'855 

 and O'SSO, the inclination between 23° and 27°, the perihelion epoch 

 between 1836-20, and 1836-45, and the period between 140 and 

 190 years." It may here be remarked that the apparent eclipse of 

 one star by the other which was observed in 1831, was not owing 

 to the passing of the plane of the orbit through the position of the 

 spectator, for all the calculations concur in giving a small inclination 

 of that plane to the surface of the celestial vault ; but to an actual 

 approach of one star to the other, for the calculations as uniformly 

 assign a large eccentricity to the relative orbit. Such an approach 

 must have enormously changed the thermotic relations of the two 

 bodies to each other. 



It will be an appropriate conclusion to this account to put in juxta- 

 position Sir John Herschel's last elements, the elements obtained by 

 Mr. Hind exclusively from Capt. Smyth's observations, and those 

 of Mr. Adams, which take for basis Sir John Herschel's orbit, and 

 are formed on the principle of distribution of errors by the method 

 of least squares. 



Elements op y Vikginis. 



Herschel. Hind. Adams. 



Perihelion passage 1836-39 1836-40 1836-34 



Ascending node 28° 42' 20° 34' 34° 45' 



Position at PeriheUon 322° 12' 323° 50' 



Inclination to plane of pro-1 g^o gg» .270 23? 25° 27' 



jection J 



Distance of Perihelion from 1 390° 30' 300° 13' 284° 53' 



node J 



Excentricity 0-8860 0-8804 0-87964 



years. years. years. 



Period of revolution 183-14 171-54 174-137 



The astronomical portion of the work concludes with a disserta- 

 tion on comets, accompanied by a representation of Encke's comet, 

 as it was seen by Professor C. Piazzi Smyth with the Hartwell Te- 

 lescope, at its reappearance on the 22nd of September 1848. This 

 comet, like Biela's and others, seems to be entirely gaseous, and of 

 such tenuity of substance that the smallest stars are visible through 

 it without sensible diminution of their brightness. 



