[272 



VAfilACLE STARS* 



it was found that the difagreements between the periods of 



change, as deduced from its full brightnefs, were much greater 



than thofe deduced from its leafl illuniinalion. The former 



gave the mean period 63 d^ys, and the latter 59| ; and the 



mean of thefe, namely 6l| days, agreeing with ihe former 



determination to | day, is as near as could be expeded in ob- 



fervations of this nature. 



7n^ Pjff^A*^ The author in the next place proceeds to examine fome 



brightnefsdo not Other of the changes to which this liar is fubject. By tabulated 



equally divide obfervations through the fame feries of years, he finds that the 



the ftar's cir- ^ 



cumference- ^'"^^ ^^ decreafe, from the middle ©f its full brightnefs to the 



they divide it as middle of its leaft, is on a mean of St days ; and that the 

 ' * time of its increafe, from the middle of its leali brightnefs to 



the middle of its full, is in like manner only 27 days. The 

 fum of thefe numbers amounting to the period 61, fhews their 

 probable exaftnefs. Thefe compared and combined with the 

 former determinations of 1796, give a mean of the whole 

 33 -{- and 29 — days. As it thus appears that the time of 

 the decreafe is longer than that of thie increafe, it follows of 

 courfe, that the places of the full and leaft brightnefs are not 

 iituated at the diftance of half the circumference from each 

 Other variable other; and the like circumftance Mr. P. affirms is found to 

 affefted. ^ ^^^ ^^^^ "^'^^ moft, if not all the variable ftars. 



The luminous The next particulars to be reviewed were the durations of 

 fdves^variabSr ^^^ brightnefs without any perceptible change, while at its 

 maximum and minimum, Thefe determinations required a 

 tolerable fucceffion of obfervations ; where that is not tlie oa(e 

 he has omitted them in his tables From thefe it is found in 

 general, that when the degree of brightnefs at its maximum 

 is lefs than ufual, and its minimum not much decreafed, the 

 changes take place but very flowly, and cannot be fettled with 

 much accuracy unlefs the obfervations have been made fre- 

 quently and with great attention. He accordingly pafTes again 

 over the feries of years, fliewing the dates of its magnitudes 

 when at its full brightnefs, and alfo when at its leaft bright- 

 nefs, aod he tabulates at the end of the firft part of his paper, 

 all the different changes that have been examined. The words 

 in the flrft column or compartment defcribe them ; in the fc- 

 cond column the prefent refults are exhibited ; in the third are 

 the refults of the former obfervations; and in the laft column 

 is placed a mean of both computed proportionally, according 

 to the number of obfervations of each. 



Table 



