Light is received from the Heavenly Bodies. 25 



as to admit of the formation of a wave at all. It appears to 

 constitute another difficulty in the way of that theory. Ac- 

 cording to the law of curvature, however, which must ren;ulate 

 the above series, there must of course be many more in- 

 tervening rays between the points corresponding with the 

 breadth of a wave in one part of the curve than in the other. 

 There must be many more in that part where the versed sine 

 increases least rapidly, near the superficial centre of the hemi- 

 sphere, than where it increases most so, near its circumfe- 

 rence; and therefore whatever effects may be due to such a 

 cause must vary also according to the points from whence any 

 given waves proceed. If any such interference does take place, 

 is it not possible that it may have some connexion with those 

 fixed dark lines which are so remarkable in the spectra of the 

 sun, and of other heavenly luminaries* ? The light of a lamp 

 is asserted to display no such lines, though there is some in- 

 equality of brightness in its spectrum, which may be due to 

 the unequal composition of the flame*. But if it appear that 

 there must be some effects produced, and such as are likely 

 to be in any degree sensible, there is room enough for specu- 

 lation and inquiry. 



I would notice one more point still. The rays proceeding 

 from the extreme edge of a luminous hemisphere, and those 

 near it, approximating almost infinitely to the position of a 

 tangent, must, for some time after their first emission, pass 

 at a very short distance from tlie surface. Now we know 

 that, in the case of bodies within our own immediate observa- 

 tion, an effect takes place under certain circumstances termed 

 iiiflcxion or diffraction^ whereby, without passing through 

 any new medium, the rays of light are bent from their course 

 by the mere passing near the surface of those bodies. One 

 should suppose, therefore, that if such an effect is produced 

 by so diminutive an object as those which have made it ap- 

 parent to our observations, the immediate neighbourhood of 

 so vast a mass of matter, for so long a time, as in the former 

 case, must produce some also upon the course of the more 

 remote rays, whether by decomposition or simple diversion. 

 If the latter alone were to take place in any degree, this again 

 would alter the apparent place of the circumference of the 

 hemisphere by the amount of the deviation. If no such effect 

 takes j)lace at all, it is a question quite as well worthy of an 

 answer, why it should be so ? And wherein consists the 

 cause of difference? 



Indeed this last remark is one whicli may be applied to the 



• Sonic observations on tliis subject l)y Sir J. F. W. Herschel will be 

 found in L. & E. Phil. Mag., vol. ill. p. 406. fcicc also vol, ix. p. 522. — Edit. 



