264' CAUSE OP THE CHANGES OF RELATIVE 



C Herculis, 

 Obfervations My obfervatlons of this (lar furnifh us with a phenomenon 



refpea'mg"the ^'^'^'^ '^ "^^ '" aftronomy ; it is, the occultation of one ftar by 

 changes of rela- another. This epoch, whatever be the caiife of it, will be 

 ftlr*stx"remel"^ equally remarkable, whether owing to folar parallax, proper 

 ■ear each other, motion, or motion in an orbit whofe plane is nearly coincident 

 with the vifual ray. My firft view of this ftar, as being double, 

 was July 18, 1782. With 460, the ftars were then | diame- 

 ter of the fmall ftar afunder. The large ftar is of a beautiful 

 Jjluifli while j and the fmall one afli-coloured. 



July 21, of the fame year, I meafured the angle of pofition, 

 20^ 42' north following. With the ftandard power, the dif- 

 tance of the ftars remained as before. With 987, they were 

 one full diameter of the fmall one afunder. 



In the year 1795, 1 found it difficult to perceive the fmall 

 ftar; however, in Odtoberof the fame year, I faw it plainly 

 double, with 460; and its pofition was north following. 



Other bufinefs prevented my attending to this ftar till the? 

 year 1802, when I could no longer perceive the fmall ftar. 

 Sometimes, however, I fufpe6ted it to be ftill partly vifible; 

 and, in September of the fame year, with 460, the night being 

 very clear, the apparent difk of ^Herculis feemed to be a lit- 

 tle lengthened one way. With the ten-feet telefcope, and a 

 power of 600, I faw the two ftars of »i Coronae very diftindlly ; 

 and, having in this manner proved the inftrument to a6l well, 

 i direfted it to ^ Herculis, and found it to have the appearance 

 of a lengthened, or rather wedge-formed ftar; after which, J 

 took a meafure of the pofition of the wedge. 



Our temperature is feldom uniform, enough to permit the uf« 

 of very high powers; however, on the llth of April, 1803^ I 

 examined the apparent dilk, with amagnifier of 21 40, and found 

 it, as before, a little diftorled; but there could not be more than 

 about I" of the apparent diameter of the fmall ftar wanting to a 

 complete occultation. Moft probably, the path of the motion is 

 not quite central; if fo, (he difli will remain a little diftorted, 

 during the whole time of the conjundion. Our prefent obferva- 

 tlons cannot determine which of the ftars is at the greateft dif- 

 tance; but this will occafion no difference in the appearance; 

 for, if the fmall ftar (liould be the neareft, its light will be, 

 equally loft in the brightnefs of the large one. 

 .''^' • ' The 



