151 



expansive river, and thus striking the drops of rain in another 

 direction ? The river was in a perfect blaze of reflected light, 

 like a mirror, at the time ; in fact, less endurable by the eye 

 than the luminary itself." 



The President observed, that the explanation suggested by 

 Mr. Blacker for this somewhat unusual phenomenon was un- 

 doubtedly the correct one. In fact, the axis of vision, as 

 it is called, — or the axis of the cone of rays which form 

 the bow, — is, in this case, the line drawn from the eye of 

 the spectator in the direction of the sun's rejected rays ; 

 and accordingly the centre of the arch is a point as much 

 above the horizon, as the centre of the original bow is below it. 

 The phenomenon is manifestly the same as if the portion of 

 the circle of the original bow, which is below the horizon, were 

 turned upwards. The arch of the extraordinary, and that 

 of the original bow, therefore, together form a complete cir- 

 cle ; the former exceeding a semicircle as much as the latter 

 falls short of it. 



The President stated, that he had found two accounts of a 

 similar phenomenon in the early volumes of the Philosophical 

 Transactions: one observed by Halley in 1698, on the banks 

 of the River Dee ; and the other by Mr. Sturges in 1792, on 

 the south coast of England. It is strange that it should not 

 have been more frequently noticed, seeing that the only con- 

 dition of its appearance (in addition to the ordinary conditions 

 of the common bow) is the presence of a reflecting surface — 

 such as the sea or a river. 



James Pim, Jun., Esq., mentioned a remarkable aurora 

 seen by him on the 19th of last month, in connexion with the 

 obscuration of the moon. 



