o/ Thomas \NY\g\\\. of Durham. 243 



The second letter is on probability and certainty, and, 

 though ingenious and sound, has nothing to the present pur- 

 pose. It concludes with an account of celestial systems ante- 

 rior to that of Copernicus. 



The third letter is on the planetary motions and structures. 

 It contains nothing peculiar to Wright, except a declaration 

 that he is strongly of opinion that the orbits of comets have 

 all their areas equal. This is not a happy conjecture. He 

 draws the notion from observing that the comets of 1680 and 

 1682, the most and least excentric of those whose orbits had 

 been calculated, have areas not very unecjual, and such as a 

 supposition of moderate errors of observation might make 

 equal. The following sentence is of a better kind, be the latter 

 part worth what it may. " . . . . the Clouds are to us in effect 

 no other than as so many Moons, whereby we have our arti- 

 ficial Day prolonged to us several Hours after the Sun is 

 set, and likewise produced as much sooner before he rises; 

 and were they to ascend by still stronger Power of Exhalation 

 to an Elevation, all round the Atmosphere, so as to form a 

 Sphere equal to four Times the Globe of the Earth, there 

 would then be no such Thing as real nocturnal Darkness to 

 any Part of the World." 



The fourth letter continues his remarks on the nature of the 

 heavenly bodies. That the sun is a vast body of blazing mat- 

 ter, he thinks will hardly admit ot question : though he after- 

 wards supposes it possible that the igneous matter may be only 

 an envelope. Aberration is spoken of with caution. " Mr. 

 Bradley, Astronomer-Royal, has, in a great measure, proved 

 that the Aberration of the Stars hitherto mistaken for a Pa- 

 rallax, may arise from, and indeed seems to be no other than 

 the progressive Motion of Light, and Change of Place to the 

 Eye, arising from the Earth's annual Motion and Direction." 

 His friend is recommended to procure an idea of the appear- 

 ance of the sun to more distant planets than our own, by 

 means of concave glasses fitted to reduce the apparent dia- 

 meter duly. The homogeneity of the stars with our sun, both 

 as to constitution and attendant bodies, is strongly insisted on 

 from analogy. 



The fifth letter first mentions the milky way, which he says 

 *'.... still continues to be unaccounted for, and even in an 

 Age vain enough to boast Astronomy in its utmost Perfection. 

 What will you say, if I tell you, it is my belief we are so far 

 from the real Summit of the Science, that we scarce yet know 

 the Rudiments ol' what may be expected from it? This lumi- 

 nous Circle has ofien engrossed my Thoughts, and of late has 

 taken up all my idle Hours; and 1 aui now in great Hopes I 



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