eOMMENTATIO ASTRONOMICA. US 



"« Tbe manner of Observation I conceive may be thus. Having first pitched liijon Ihe 

 r Star we mean to observe, and liaving tlien considered (which is not hard lo do ) 

 «■■wheire sueh-staris t» be- seen in its grealest aast or west azimuth; it may be thea 

 « canvenient to fix ( Vfery firm and steadily on some lower, steeple , or other hif^h 

 « edifice, in a coavenient Situation) a good telescopick object-glass in such position, 

 « as may be proper fbr viewing Ihat star. And at ä due distance fVom it near the 

 « ground, build on purpose ( if already there be not any) some liltle stone wall, or 

 « l*k<e pkoe, on- whieli to fix the eye-glasS', so as to answer that object-glass. And ha- 

 « ving' so adjusied it, as through both to see that st;ar in its desired statio», (which 

 « raay best be done while the slar is to be secn by night ii> such Situation , near the 

 « time ofoneof the solstices), let it be there fixed so firmly, as not to- be disturbed 

 t, (and tihe plhce sosecured, as that none eoineto disorder it) , and care be taken so to 

 (r defend both the glasses , as not to be endangered by wind and weather. In which coii- 

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

 « advTce and assistauce; with whom I have many years since, communiGated Ihe whole- 

 « matter. " 



« This glass being once fixed (and a micrometer fitted lo il, so as to have ifs threds 

 « perpendicular to the horizon , to avoid any inconvenience which might arise from di- 

 « versity of refraction if any be) the star may then be viewed from time to time (fop ih^ 

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



« This I thoughl fit to- recommend to your consideration , wha do- sO' well undersland 

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

 « duce it lo praetice. If you shall tliink fit to give your seif the trouble of attemptin" 

 « the experiment, and that ic succeed well, it will be a aoble Observation, and worth 

 V the labour. And, if it should miscarpy , ihe charge I hopc would not be great. " 



« But when I suggesi ( as a convenient star for Ihis purpose) the Shoulder of the 

 « lesser Bear ( as being the nearest- to the pole of llie zodiack of any star that is of the 

 « firet or second magnitude) , I do not oonfine you to that star: but ( wilhout retract- 

 (( ing that) suggest anolhcr ; naraely, the middle star, in the tail of the great Benr 

 « which (thoogh somewhat farthei fi-om the pole of the zodiack} is a brigliter star 

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



« But I do it prineipally upon this consideration : namely , that iKere Ts adherin» to- 

 « it a very small slar, (whirh the Arabs call Alcor , of which they have a provcrbial 

 « saying, when they wonld describe a- sharp-sighled man; that he ccui ilisceTn the ii- 

 <s. (hr on the middle Korse of Ihe wayn ; and of one who pretends lö see small ihino-s 

 « but, over look much greater ; vidit AJcor at noii Lunam plenam) . which Heve- 

 «. ILus in his observalioüs, fioda to: be distant from it nbout d-minules;,. and 5 or 10- 



« sc» 



