110 HISTORY OF OPTICS. 



>ter a iHic -property of ///////, is completed in tlic Philosophical 

 Magazine for November, 1S4G. It is there shown that a, dependence 

 of the breadth of the bands upon the aperture of the pupil, which 

 had been supposed to result from the theory, and which does not 

 ;iM'car in the experiment, did really result from certain limited con- 

 ditions of the hypothesis, which conditions do not belong to the 

 experiment ; and that when the problem is solved without those 

 limitations, the discrepance of theory and observation vanishes ; so 

 that, as Mr. Airy says, "this very remarkable experiment, Avhich long 

 appeared inexplicable, seems destined to give one of the strongest 

 confirmations to the Undulatory Theory." 



I may remark also that there is no force in the objection which has 

 been urged against the admirers of the nndulatory theory, that by the 

 fulness of their assent to it, they discourage further researches which 

 may contradict or confirm it. We must, in this point of view also, 

 lok at the course of the theory of gravitation and its results. The 

 acceptance of that theory did not prevent mathematicians and 

 observers from attending to the apparent exceptions, but on the con- 

 trary, stimulated them to calculate and to observe with additional 

 zeal, and still does so. The acceleration of the Moon, the mutual 

 disturbances of Jupiter and Saturn, the motions of Jupiter's Satellites, 

 the effect of the Earth's oblateness on the Moon's motion, the motions 

 of the Moon about her own centre, and many other phenomena, were 

 studied with the greater attention, because the general theory was 

 deemed so convincing : and the same cause makes the remaining ex- 

 ceptions objects of intense interest to astronomers and mathematicians. 

 The mathematicians and optical experimenters who accept the nndu- 

 latory theory, will of course follow out their conviction in the same 

 manner. Accordingly, this has been done and is still doing, as in 

 Mr. Airy's mathematical investigation of the effect of an annular 

 aperture ; Mr. Earnshaw's, of the effect of a triangular aperture ; Mr. 

 Talbot's explanation of the effect of interposing a film of mica be- 

 tween a part of the pupil and the pure spectrum, so nearly approach- 

 ing to the phenomena which have been spoken of as a new Polarity 

 of Light ; besides other labors of eminent mathematicians, elsewhere 

 mentioned in these pages. 



The phenomena of the absorption of light have no especial bearing 

 upon the undulatory theory. There is not much difficulty in explain- 

 ing the 2)ossibility of absorption upon the theory. When the light 

 is absorbed, it ceases to belong to the theory. 



