COMMENTA-TIO ASTRONOMICA. 143 



•s^i'Tli? maiiner of Observation l conceive may be ihus. Having first pitched ^upon ihes 

 v-stai' ~wä meaM tb observey aildhaning thea considered (which. is not hard to de). 

 « where such Star is to be seen in its greatest east er -west azimulh; it may be thea, 

 « convenient to fix (■ very firm and steadily on some tower, steeple , or otber bigh 

 Ä edifice, ia a convenient situalioa)- a: good telescopick object-glass in such position,, 

 (< as may be proper för viewiiig that slar. And at a due distance from it near the 

 « «round, build on purpose (: if already ihere be not any) some liltle stone wall, or 

 *• like place,,, on: which to fix the eye-glass, so as to answer that object-glass. And ha- 

 « ving' so adtjustedit, as through both to see that star in its desired Station, (wJiich 



• may- best be done while the slar is to be seen by night in such Situation , near the 

 fi. lim«' oCone of the solsliqes) , let it be thei« fixed so fiimly, as laot to, be distorbed,, 

 •^ (and! the pfeice so secured , as that none eome to disorder it ) , and care be taken so to 

 « defead both the glasses, as not to be endangered by wind and wealher. In which coii- 

 « trivance I am- beholden to Mr. John Caswel M. Ä. of Hart-hall in Oxford, for his 

 «adtifeo »ttd assistane«; with whom. I bave many years since, communicated the whola 

 «matter, "^ 



« This glass beuig once fixed (and a micrometer fitled to- it, so as to bave its threds 

 c< perpendicular to the horizon, lo avoid any inconvenience which might arise from di- 

 « versity of refraction if any be) the slar may then be -viewed from time to time ( for Ihe 

 « followmg year or longer ) to see if any change of azimuth can be observed. " 



• «f Tos I Ihought fit torecommend lo your consideration , who do so well understand 

 « lelescopes, and the managery of them; not knowing any who is more likely to re- 

 « düOe it lo practicei If you shaU Uiink fit to give your seif the trouble of attempling 

 « lue experime»», «nd that it succsed well, it will be a noble Observation, and wortbi 

 V the labeur. Andl, if it sheuld miscarry , the eharge l hopc would not be great." 



« But when I suggest ( as a convenient star for tbis purpose) the Shoulder of the 

 ü lesöer Bear (as being the nearest to the poje of tbe zodiack of ^,ay star that is of the 

 « first' or secondmagnilude);, I do not cönfine you to that star: but ( wilhout retract- 

 « in" that) suggest another ; namely, the middle star, in tbe tail of the great Bcar^ 

 « wiiiol» (theugh somewhat falrtheit •fr<MB Ihp ijol« flf the zodiack), is a brighter s^ar 

 « than the olher , and may be nearer to us. " 



« But I do it prineipally upon Ihi» consideration: namely, that there is adhenng to- 

 « it a very small star, (whirh the Ara.bs caH Alcor , of which they have a provcrbial' 

 « sayitig , when they wQuld describe a sharp-sighted man ; llial he ca^n iKsr.ern the ri- 

 « der on the middle Korse of the wayn ; and of one who pretends to see sraall ihings 

 «but over look much^ grealer ; vidit Alcor at non Lunavi plenam) -. which Heve- 

 «Bus iu. his observatious, finds ta be distaul from- it about &minules, and 5 or 10* 



» 38*- 



