INTRODUCTION. 



XXIX 



Still acknowledging that we know not what nebulous matter is, and therefore that we cannot, 

 with certainty, argue about its properties of reflection; yet still claiming as a high probability, 

 amounting almost to certainty, that the laws of reflection, applying to all other bodies, to 

 solids, to vapors, to the molecules of our atmosphere, apply also to nebulous matter, we find in 

 the above table a strong argument for such a ring around the earth. The figures, taking either 

 of the two columns, for water or for glass, correspond in a very striking degree with the 

 van-in" 1 intensity of the Zodiacal Light, from the base upward, as we have it on any clear 

 mornino- O r evening when the ecliptic is at a high angle with the horizon, and when, conse- 

 quently, the nebulous figure is not brought angularly to our eye. They also correspond to 

 what is, indeed, almost synonymous with that which has just been stated namely, to the fact, 

 that at 4'' 30 m , the Zodiacal Light at the horizon is far greater at its base than it is at 

 3" 30 m ; at 3" 30 m , than it is at 2" 30, &c., back to midnight. Any person, who has ever 

 looked attentively at this Light, when making a high angle with his horizon, will see at once 

 the coincidence between the proportions in the above figures, showing the number of reflected 

 rays, and what has been always presented to his eye. If the reader will also carry these lines 

 of incident and reflected light beyond the midnight horizon-line, to any point there of the 

 nebulous ring, he will see how we may easily get what is referred to in my charts under the 

 German name of gegenschein i. e. a dim light, seen, when the circumstances are favorable for 

 it, in those portions of the sky opposed to the sun. This hypothesis shows also, very clearly, how 

 I could have the Zodiacal Light above both horizons at the midnight hours, as I was often able 

 to do, and it harmonizes fully with the strength of the Light as then presented to the eye. 



Indeed, while Bouguer's results are antagonistic to all the theories discussed in the previous 

 sections, and seem to be utterly irreconcilable with them, they fully coincide with this, in every 

 one of its aspects ; and, so far as they can go, they satisfy the mind, in all the varying characters 

 of the Zodiacal Light. 



I said, so far as they can go ; for there are points in this subject, such as the pulsations 

 of light, and what in the annotations to these charts is called the " effulgent light," which 

 belong to something in the nebulous matter which we have not yet fairly reached, and which 

 must be left for explanation to yet further observations. 



While there are some things still left unexplained, I have, yet, not been able to see any thing 

 in this hypothesis antagonistic to the facts of the Zodiacal Light. On the contrary, almost all 

 of them are explained by it; and they all, as far as I can perceive, fully harmonize with it, 

 through the whole of the manifold changes which the light underwent, either from the changes 

 of the ecliptic towards any fixed spot, or from my numerous and great changes of latitude 

 during our cruise. But, for this, I must refer the reader to the charts and annotations of this 

 hunk. In examining them in detail, we must n'!ii<'inbf>r the deduction just drawn in I, from 



