140 HERSCrtfcL ON COLOURED RlNf.S. 



seen comes either from 1, 2, or 3, or from all these places to- 

 gether, and being reflected at 4, 5, and 6, rises up by trans* 

 mission to the point of contact at 7, where the rings are 

 formed. Here they are both transmitted tip to the eye at 8, 

 and reflected down to 9 ; from 9 they are reflected up to 10 

 and transmitted down to 11 ; from 11 they are reflected to 1 J 

 and transmitted to 13 ; and lastly, from 13 they are reflected 

 to 14 ; so, that again four sets of rings will be seen at 8, 10, 

 12, and 14. 



This being a theoretical way of conceiving how the rays 

 of light may produce the effects, it will be required to show 

 by experiments, that this is the actual progress of the rays, 

 and that all the sets of rings we perceive are really reflected 

 or transmitted in the manner that has been pointed out ; 

 but as we have so many reflections and transmissions. be- 

 fore us, it will be necessary to confine these expressions to 

 one particular signification when they are applied to a set of 



and transmit 

 tech 



What is meant When the centre of the rings is seen at the point of con- 

 by reflected tact, it is a primary set; and 1 call it reflected, when the 

 rays which come to that point and form the rings undergo 

 an immediate reflection. But I call it transmitted, when 

 the rays, after having formed the rings about the point of 

 contact, are immediately transmitted. 



Thus in figure 3 and 4 the rays a b c, d e f, give reflected 

 sets of rings; and the rays g h i, k I m, in figure 5 and 6, 

 give transmitted sets. 



In this denomination, no account is taken of the course of 

 the rays before they come to a, (J, g, k; nor of what be- 

 comes of them after their arrival at c, f 9 i, m : they may 

 either come to those places or go from them by one or more 

 transmissions or reflections, as the case may require ; but our 

 denomination will relate only to their course immediately af- 

 ter the formation of the rings between the glasses. 



The secondary and other dependent sets will also be called 

 reflected or transmitted by the same definition : and as a set 

 of these rings formed originally by reflection may come to 

 the eye by one or more subsequent transmissions; or being 

 formed by transmission, may at least be seen by a reflection 

 from some interposed surface, these subsequent transmissions 



