HERSCHEL ON COLOURED RINGS. 





XII I. Of the order of the Colours. 



The arrangement of the colours in each compound ring or The most re- 

 alternation, seen by reflection, is, that the most refrangible frangible rays 



. J , \ . , • ■ . ■ • , rt , nearest the 



rays are nearest the centre; and the same order takes place centre 

 when seen by transmission. We have already shown, that, 

 when a full dilution of the colours was obtaiued, their ar- 

 rangement was violet, indigo, blue, green, yellow, orange, 

 and red ; and the same order will hold good, when the co- 

 lours are gradually concentrated again ; for though some of 

 them should vanish before others, those that remain will al- 

 ways be found to agree with the same arrangement. 



If the rings should chance to be red and green alternately, 

 a doubt might arise, which of them is nearest the centre ; but 

 by the method of dilution, a little pressure, or some small in- 

 crease of the focal length of the incumbent lens, there will 

 be introduced an orange tint between them, which will im- 

 mediately ascertain the order of the colours. 



In the second set of rings the same order is still preserved ia all cases, 

 as in the first ; and the same arrangement takes place in the 

 third set as well as in the fourth. In all of them the most 



refrangible rays produce the smallest rings. 



t » 



XIV. Of the alternate Colour and Size of the Rings belong-' 

 ing to the primary and dependent Sets. 



When two sets of rings are seen at once, and the colour Alternation of 

 of the centre of the primary set is black, that of the secon- the depep'Hwt 

 dary will be white; if the former is white, the latter will be ^j ^J^ ° r 

 black. The same alternation will take place if the colour, of 

 the centre of the primary set should be red or orange ; for 

 then the centre of the secondary one will be green ; or if 

 the former happens to be green, the latter will be red or 

 orange. At the same time there will be a similar alternation , 



in the size of the rings ; for the white rings in one set will be 

 of the diameter of the black in the other ; or the orange 

 Tings of the former will be of equal magnitude with the 

 green of the latter. 



M lien three sets of rings are to be seen, the second and 

 third sets will be alike in colour and size, but alternate in 

 both particulars with the primary set. 



Tne 



