VOL. X.] PHILOSOPHICAL TRANSACTIONS. 213 



5. Therefore, these colours arise from the solar beams; but not from them 

 alone, as was hitherto thought, but also from the rays of the air itself, surround- 

 ing the solar body. 



6. But neither do these colours arise from all the rays, whether solar or aerial, 

 which enter the drop; but only from such as are emitted from the solar limb 

 itself, and from the air adjacent to it. 



7. But such rays as are thus transmitted from the solar limb, and the neigh- 

 bouring air, into the drop, do not all belong to the said colours, nor do they 

 escape coloured; but such only, whose angle of incidence is neither less than 

 45°, nor greater than 75°. 



8. Therefore the rainbow colours proceed from the solar limb and the adja- 

 . cent air, yet all the five do not immediately flow from thence; but four only, 



viz. red, yellow, blue, and purple ; for the green arises from a mixture of the 

 yellow and blue rays. 



g. Therefore these four colours arise from the said limb; though not all 

 from one and the same part: but two of them from one part of the limb, and 

 other two from that directly opposite; viz. the blue and purple arise from the 

 upper limb ; and the red and yellow from the lower. 



10. And there seems to be no other reason of this, viz. why from limbs so 

 very like, dissimilar rays should arise; but that in one case, the aerial limb is 

 above the solar ; and in the other case, the solar above the aerial. And this 

 difference seems to be sufficient, because on account of that different situation, 

 at one time the solar rays may be bent by refraction above the aerial rays ; and 

 at other times on the contrary, the aerial above the solar. 



11. Therefore these colours arise by means of the said refracted rays, yet so 

 refracted, that by that refraction they are very much crowded together. For 

 all the rays, from the 45th degree to the 6oth, are in the less ring contracted 

 into the space of one degree ; into which narrow space, all the rays, from the 

 60th to the 75th degree, concur by retrogradation. 



12. There are as many rainbows at once, as there are spectators. 



13. A spectator observes at each moment a different rainbow. 



Observations of a Lunar Eclipse, made at Paris, and compared with those made 



at London, June 26, l675, 0. S. noticed in Numb. \l6 of these Abridgements, 



p. 221. N*" 117, p. 388. 



These observations were made by Messrs. Cassini, Picard, and Romer. By 

 which it appears, that the beginning of the eclipse was at 1 h. 56m. 45 s. after 

 midnight, and the total immersion, or internal contact, at 3h. 7 m. 45s. 



They may be useful for determining the difference of longitude between the 



