444 MR. THOMAS HEELIs's OBSERVATIONS 



tion of the envelope, that one limb of it generally appeared 

 before the other, seem to militate strongly against the idea 

 that the light is caused by a nebulous atmosphere sur- 

 rounding the sun, but might be explained by the theory of 

 the light being caused by a ring of asteroids. 



The light of Jupiter and Saturn, which during most 

 of the observations were very near together, interfered 

 at times considerably with the observations; and I was 

 obliged to take precautions such as hiding the planets, 

 especially Jupiter, behind some intervening object, or to 

 avail myself of a passing cloud, in order to arrive at satis- 

 factory results. On the 17th July especially my note- 

 book records that " The southern limb of the envelope 

 is brighter than the northern ; but this is caused by the 

 light of Jupiter ; and if the planet be concealed behind any 

 object, the envelope becomes distinctly visible ; but it is 

 so delicate an object, that I cannot compare the brightness 

 with anything. As a coarse estimation, I should say that 

 it was not more than one-third of the brightness of the true 

 light. This envelope was visible after the setting of Jupiter, 

 and at times I thought that it extended to the meridian 

 of Spica Virginis.^' And again, on the 24th July, I find 

 an entry respecting the inner cone as follows : — ^^ Apex 

 apparently not symmetrical, no light appearing near Saturn, 

 so that the top from and towards v Leonis appeared con- 

 cave ; but this may have been caused by the light of 

 Jupiter, then near Saturn." At times no trace of the 

 envelope could be observed to extend beyond the apex of 

 the cone; and its existence on such occasions was only 

 manifested by very delicate shading along the limbs of the 

 latter. At other times, as on the evening of the 27th 

 July, this occurred and was noticed while I was observing 

 the main body of the light, and the extension of the 

 envelope beyond the apex manifested itself as the night 

 wore on. 



