J20 ON TWO CELESTIAL BODIES. 



XI. 



Obfervations on the two lately difcovered celejlial Bodies. By 

 William Herschel, LL. D. F. R, S. 



The moving ftar J.N ni y early account of the moving ftar difcovered by Mr. 



jninute. Piazzi, I have already (hewn that it is of a remarkably fmall 



fize, deviating much from that of all the primary planets *. 



It was not my intention to reft fatisfied with an eftimation of 

 the diameter of this curious object, obtained by comparing it 

 with the Georgian planet, and, having now been very fuc- 

 cefsful in the application of the lucid difk micrometer, I fhall 

 relate the refult of my inveftigations. 



Another difco- j^t the very interefting difcovery of Dr. Olbers having in- 



Olbers/ ' troduced another moving ftar to our knowledge, I have ex- 

 tended my refearches to the magnitude, and phyfical con- 

 struction, of that alfo. Its very particular nature, which, 

 from the obfervations I fhall relate, appears to be rather co. 

 metary than planetary, will poftibly throw alfo confiderable 

 light upon the circumftances belonging to the other celeftial 

 body; and, by that means, enable us to form fome judgment 

 of the nature of both the two laft difcovered phenomena. 



As the meafures I have taken will oblige me to give a refult 

 which muft appear extraordinary, it will be highly neceflary 

 to be particular in the circumftances of thefe meafures, and to 

 mention the condition and powers of the telefcopes that were 

 ufed to obtain them. 



Magnitude of the new Stars. 

 Obfervations on April 1, 1802. Having placed a lucid difk at a confider- 



with a°E red able diftance from the e y e > but fo that l mi g ht vievv Jt With 



di/k. perfect diftinctnefs, I threw the image of Mr. Piazzi's ftar, 



7-feet refiedtor. feen in a 7-feet refledtor, very near it, in order to have the 

 projected picture of the ftar and the lucid difk fide by fide, 

 that I might afcertain their comparative magnitudes. I foon 

 perceived that the length of my garden would not allow me to 

 remove the diik-micrometer, which muft be placed at right 



* By comparing its apparent difk with that of the Georgian pla- 

 net, it was eftimated, that the real diameter of this new ftar could 

 not amount to three-eighths of that of our mcon. 



angles 



