170 



Dr. Herschel, having made these preliminary experiments, pro- 

 ceeds to apply them to investigate the nature and magnitude of the 

 star lately discovered by Mr. Harding. A regular series of obser- 

 vations on this star are detailed, beginning on the 29th of September, 

 ,and ending on the llth of October. Of these we must necessarily 

 confine ourselves to mention merely the general result with the con- 

 clusions deduced by the author from the whole of the investigation. 

 These conclusions are as follows : 



1. A ten-feet reflector will show the spurious or real discs of ce- 

 lestial and terrestrial objects, when their diameter is one fourth of a 

 second ; and in favourable circumstances that diameter may be di- 

 vided, by estimation, into two or three parts. 



2. A disc of the above diameter, whether spurious or real, to be 

 seen as a round well-defined body, requires a magnifying power of 

 500 or 600, and must be sufficiently bright to bear that power. 



3. A real disc of half a second in diameter will be so magnified 

 by the above-mentioned power, that it may be easily distinguished 

 from a spurious one of equal size, the latter not being affected by 

 magnifying power in the same proportion as the former. 



4. The different properties of the inside and outside rays of a 

 mirror, with regard to the appearance of a disc, will show whether 

 it is real or spurious, provided its diameter is more than one-fourth 

 of a second. 



5. When discs, either spurious or real, are less than one fourth of 

 a second in diameter, they cannot be distinguished from each other, 

 because the magnifying power is not sufficient to make them appear 

 round and well defined. 



6. The same kind of experiments are applicable to telescopes of 

 different sorts and sizes, but will give a different result for the quan- 

 tity here stated at one fourth of a second, being more when the in- 

 strument is less perfect, and less when it is more so. 



The general results of Dr. Herschel's observations on Mr. Harding's 

 newly discovered celestial body, to which the name of Juno has been 

 given, are, 



1. That it is in every respect similar to those discovered by 

 Mr. Piazzi and Dr. Olbers, so that Ceres, Pallas, and Juno, are cer- 

 tainly three individuals of the same species. 



2. That these bodies (the last of which appears to be the smallest,) 

 are incomparably smaller than any of the planets ; for a telescope that 

 will show a diameter of one fourth of a second, will not determine 

 whether their discs are real or spurious, although a power of more 

 than 600 has been applied to each of them. 



3. That the criterion of the apertures of the mirror has, on account 

 of the smallness of the object, been equally unsuccessful ; every me- 

 thod that has been tried only proving their resemblance to small stars. 



4. That the definition of the term asteroid, formerly given by 

 Dr. Herschel, will equally express the nature of Juno, which, on ac- 

 count of its similar situation between Mars and Jupiter, and its de- 

 parture from the general condition of planets, by the smallness of its 



