VOL. XVII.] PHILOSOPHICAL TRANSACTIONS. 563 



same cause of complaint. I know that Dr. Hook and Mr. Flamsteed have 

 attempted somewhat that way, but have desisted before they came to any thing 

 of certainty. 



Galileo has suggested several things towards it. As to the times of o!)Ser- 

 vation ; that it should be when the sun or earth are in the tropics, or nearly so ; 

 because at those times, if at any, will be the greatest difference in their me i- 

 dional altitude. As to the stars to be observed : that they should be such as 

 are as near as may be to the pole of the ecliptic ; for such as are in the plane of 

 it, or nearly so, though they may be sometimes nearer, sometimes farther from 

 us, which might somewhat alter their apparent magnitude, if it were at all 

 observable, yet it would little or nothing alter the parallactic angle. Galileo 

 also observes, that in a business so nice, the ordinary instruments of observa- 

 tion might be insufficient for this purpose ; and he proposes, that by the side of 

 some edifice or mountain, at some miles distance, the setting of some noted 

 star, as that of Lucida Lyrae, might be observed at those different times of the 

 year, which might be equivalent to an instrument whose radius is so large. 

 This might be a good expedient if practicable ; but I doubt the density of our 

 atmosphere is so great, that it will be hard to discern a star just at the horizon, 

 or even within some few degrees of it, and that the refraction would be there 

 so great, and so uncertain, as not to answer so curious an observation. 



What occurred to me on these considerations was this, that some circum- 

 polar stars, nearer to the pole of the equator than our zenith, and not far from 

 the pole of the zodiac, should be made choice of for this purpose. And in 

 case the meridional altitude be discernibly different at different times, so will 

 also be their utmost east and west azimuth, which may be better observed than 

 their rising or setting ; and this will be not obnoxious to the refraction, as the 

 meridional altitude is, and we may here have choice of stars for the purpose, 

 which in observations from the bottom of a well we cannot have, being there 

 confined to those only which pass very near our zenith, though very small 

 stars. 



I would then take it for granted, as a thing at least very probable, that the 

 fixed stars are not all at the same distance from us ; but the distance of some 

 vastly greater than of others, and consequently, though the parallax of the more 

 remote, may be undiscernible, it may perhaps be discernible in those that are 

 nearer to us. And those we may reasonably guess to be nearest to us, which 

 appear largest and brightest, as are those of the first and second magnitudes ; 

 and there are, at least of the second magnitude, pretty many not far from the 

 pole of the ecliptic, as that in particular in the shoulder of the Lesser Bear ; 

 and in case we fail in one, we may try again and again on some others ; which 



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