409 PHILOSOPHICAL TRANSACTIONS. [aNNO iSS/. 



siderably differing in latitude can be supposed, wherein if there be any sensible 

 motion of the poles, it shall not be perceived by the alteration of the latitude 

 of one or both of them. 



The accurate Mr. Wurtzelbaur has lately furnished us with the means of 

 examining this hypothesis by observation, having sent us the meridian altitudes 

 of ttie sun, taken at Nurenburg, about the two solstices in the year 1686. 

 June the 10th he found the meridian altitude of the sun 64° 1' IQl', and the 

 next day 64° 2' 'lb", and on December 14th, 3 days after the solstice, wherein 

 the sun was got two minutes higher, he found the meridian altitude 17° 9' 10"; 

 therefore the solstitial altitude was 17° ^' 10". These heights were taken by an 

 instrument of 6 feet radius, of brass ; and the skill and diligence of the observer 

 are not to be doubted. 



To compare with these, I find among Bernard Walthers' observations, made 

 in the same city of Nurenburg, 200 years before, viz. in the year 1487, that 

 the meridian altitude of the sun, in the summer solstice, was observed by 

 Ptolomy's parallactic instrument, when the chord of the sun's distance from the 

 zenith was observed 44890 parts of lOOOOO radius ; the same being confirmed 

 by the concurrence of the observation of several years both before and after. 

 The arch answering to this chord, gives the sun's distance from the zenith 

 25° 56' 30", and consequently the meridian altitude, its complement to a 

 quadrant, 64° 3' 30". Again the same year 1487, the chord of the meridian 

 distance of the sun from the zenith, on the day of the winter solstice, was 

 found 118790, confirmed likewise by many subsequent observations; the arch 

 answering to this chord is 72° 52' 40", and its complement 17° 7' 20", the meri- 

 dian height of the sua in the winter solstice. 



Hence it appears that the solstitial heights were very nearly the same at 

 Nurenburg 200 years ago, as they are now, that of the summer solstice being 

 but one minute different, the other only 10", both which may possibly arise 

 from the defects of the instruments of these observers, being made with plain 

 sights ; but what I shall necessarily conclude from hence is, that if there be 

 such a motion of the poles, it is either very slow, or else nearly at right angles 

 to the meridian of Nurenburg; in which latter case, the latitudes of places 

 about Tunking, Siam, Malacca, and Java on the one side, and in our American: 

 plantations of New-England, Virginia, Jamaica, &c. on the other, ought to 

 change fastest ; but I have never yet heard of any such thing observed by any of 

 our navigators ; whence if there be such a change of the earth's poles, it must 

 necessarily require a long time to become sensible. 



Besides, from these observations it appears that the obliquity of the ecliptic 

 has continued unaltered for these 200 years last paat,. that is to say, that the 



