H 



G, Jones on the Zodiacal Light 381 



the horizon 1*^ 20"^ after sunset, the angle between the incident 

 ray from the sun to B and the reflected ray BE will be 15^ ; be- 

 tween the incident ray to F, and EF will be 25° ; at 

 is Se""; and higher up, at I it is 45°; and at K it is 

 Thus the angles between the incident and reflected rays go on 

 increasing from the horizon up to K. The table of reflected 

 rays which Bouguer has furnished us as the result of his experi- 

 ments shows but little difference of the amount of light reflected, 

 where the difference in angularity is so small, as in these cases ; 

 but supposing that there is no difference at all and that the light 

 is equal from B to K, this would be in opposition to the facts of 

 the case, which are uniformly that the Zodiacal Light is very 

 strong, often quite effulgent at B, and goes, losing its intensity as 

 it ascends towards the zenith of the spectator. The fact is most 

 clearly obvious, that the Zodiacal Lignt requires, by the laws of 

 reflection, an hypothesis which will give us the angle between 



tue incident and retlected light, at 13 greater than at Jj ; at F 

 greater than at K, and so diminishing upward ; which is done, 

 as we shall presently see, by a geocentric ring : a heliocentric 

 ring must always give us the very reverse of this. This latter 

 and long admitted theory would give us only a Zodiacal Light 

 wide at the zenith and tapering to a point at the horizon next 

 the sun : and moreover brightest above, and losing its brightness 



utterly contrary to facts. 



are 



Luminous 



K 



A 



dawn. The part B of the Zodiacal Light towards the sun would 

 he extremely narrow, almost or quite a vanishing point, while 

 the part at A would have the width AC — which we may sup- 

 pose to represent the breadth of the nebulous ring. 

 The annexed Plate No. 6, will help to show how these laws of 



as 



ing the earth for its centre ; and how completely, in this case, 

 they coincide with the facte of the Zodiacal Light, as exhibited 

 in any latitude. The reader, if he is not flimiliar with this phe- 

 nomenon may test the subject by using Prof. Olmsted's plate of 

 the Zodiacal Light in the volume of the Am. Journ. of Science for 

 1851, p. 309, which is a fair exhibition of the Zodiacal Light in 

 high northern latitudes ; at the equator the appUcation of these 

 laws of reflection is much more striking and decisive. 



In this plate, the inner belt BE, HI, AK, may be considered 

 ^ representing the Luminous Arch presented to the eye. If 

 AB be the spectator's horizon an hour and twenty minutes after 

 sunset — say at 7^ 20"^, then C I m, B II m may represent the shape 



of the Zodiacal Lioht as usually shown in latitudes somewhat 



