1871J The Eclipse of Last December. 245 



delicate, in fact, than any tint which the most skilful engraver 

 could produce ; and a very slight additional atmospheric 

 illumination would suffice to add to the apparent extension 

 of the corona. Now we have only to conceive the actual 

 nature of the illumination of our atmosphere during totality 

 bythe bright innercoronato see that towardstheend oftotality 

 the light thus arising would be much stronger on the west 

 than on the east,— so much stronger, we may readily believe, 

 as to veil in some sort the features of the actual radiated 

 corona on that side, and seemingly also to increase its ex- 

 tension. 



This, indeed, seems the only available explanation. For 

 though Dr. Oudemann has suggested that matter between 

 the earth and moon may explain the peculiarity — which was 

 first observed in the eclipse of 1715, and has since been 

 recognised in nearly all total eclipses — there are overwhelm- 

 ing objections against his theory. Those I am about to urge 

 do not, indeed, apply to the theory as understood by Professor 

 Young, who in the paper from which I have already quoted, 

 remarks that a light cloud of cosmical dust, one or two hundred 

 thousand miles above the earth's surface, and of great 

 thickness, would account for observed peculiarities other- 

 wise not easily interpreted. This is just, but nothing 

 could account for such a cloud as a regular attendant of the 

 earth and always lying towards the moon's place in total 

 eclipses. Dr. Oudemann's theory is very different, and is 

 also in itself far more plausible. For he supposes the cosmical 

 dust to occupy the whole space between the earth and the 

 sun, — to form, in fact, such a lenticular disc around the sun 

 as astronomers have long been familiar with in theories 

 explaining the zodiacal light. Not only is there no im- 

 probability in the general supposition, but, on the contrary, 

 it may be regarded as absolutely certain that space around 

 the sun, as far as our earth and farther, is in reality so 

 occupied. 



But to Oudemann's theory, propounded by way of ex- 

 plaining the peculiarities of the corona, there is an over- 

 whelming objection. If we suppose that e (fig. 10), is the 

 earth, m the moon, and s the sun, (the dimensions of these 

 bodies, and the distance e m being enormously exaggerated 

 compared with the distance m s), then whatever light might 

 be supplied during total eclipse from a space e m full of the 

 supposed cosmical dust, would be altogether surpassed by 

 the light comingfrom the prolongation of the space e m towards 

 s, up to, and past s. And this not only because the latter 

 regions of space are so much more extended, but because 



