252 On a Method of viewing Newton's Rings. 



use white light for the generation of the rings and the sub- 

 ordinate systems, we can predict the result : for colour will be 

 visible in any of the images of the slit B 1? B 2 , C b C 2 , &c. at the 

 points of intersection of the dark curves when it has faded 

 elsewhere. Hence co-major-axial hyperbolic broken lines of 

 colour must result, since the various sets of curves in mono- 

 chromatic light are intersecting systems of circles whose 

 centres lie in one straight line. As the systems considered He 

 more and more remote from the primaries, the first hyperbola 

 formed will be intersected by others, their numbers ever in- 

 creasing, till, finally, the whole space considered is so full of 

 them that it seems everywhere pervaded by faint white light. 

 The results obtained by the experiments described in this 

 paper may be briefly stated as follows : — 



(1) The method gives a very simple method of viewing 

 Newton's rings by the light emitted from the two 

 interior surfaces of the glass plates, free from all other 

 light, except only that due to reflexions in the air- 

 space. 



(2) It reveals to the eye (for the first time) the subordinate 

 interference systems which coexist with the primary 

 rings, and demonstrates which of these reflexions must 

 be taken into account in framing the theory of the 

 rings as they are generally viewed. 



(3) It supplies a method of analysing these systems ex- 

 perimentally. 



(4) It shows that most probably the interference of mono- 



chromatic light in forming the rings is never absolutely 

 complete, though very nearly so. 



Note. — The photograph (fig. 6) of the interference systems was 

 taken by the light of sodium chloride, volatilized in aBunsen flame. 

 The exposures being for A 2 , B 1S and B 2 , 10 min., 60 min., and 240 miD. 

 respectively. The thickening of some of the lines at certain points 

 in Bj and B„ is due to the faint blue light of the Bunsen burner. 

 It is mcst noticeable in the immediate neighbourhood of the central 

 spot. The plates used were Edwards's isochromatic medium, stop 

 f/8. The illustration is an enlargement from 1| in. x \ in. 



Eton College, Windsor. 

 March 11th, 1898. 



