Royal Astronomical Society. 255 



its existence, detected the sixth star of the trapezium of 

 6 Orionis. And with this, under a magnifying power of 450, 

 and in very unfavourable circumstances of altitude, both him- 

 self and Mr Dawes became satisfied of the division of the ex- 

 terior ring of Saturn into two distinct annuli, a perfectly 

 clear and satisfactory view of the division being obtained. 



The feats performed by the larger instrument have been 

 much more remarkable and important. It has established 

 the existence of at least one of the four satellites of Uranus, 

 which since their announcement by Sir W. Herschel had been 

 seen by no other observer, viz., the innermost of all the series, 

 and afforded strong presumptive evidence of the reality of 

 another, intermediate between the most conspicuous ones. 

 The observations of M. Otto Struve, if they really refer to 

 the same satellite, are of nearly a month later date. 



To Mr LasselFs observations with this telescope we also 

 owe the discovery of a satellite of Neptune. The first occa- 

 sion on which this body was seen was on the 10th of October 

 1846, but owing to the then rapid approach of the planet to 

 the end of its visibility for the season, it could not be satis- 

 factorily followed until the next year, when, on the 8th and 

 9th of July, observations decisive as to its reality as a satel- 

 lite were made, and in August and September full confirma- 

 tion was obtained. This important discovery has since been 

 verified both in Russia and in America. I call it so, because, 

 in fact, the mass of Neptune is a point of such moment, that 

 it is difiicult to overrate the value of any means of definitive- 

 ly settling it. Unfortunately, the exact measurement of the 

 satellite's distance from the planet is of such extreme diffi- 

 culty, that up to the present time astronomers are still con- 

 siderably at issue as to the result. 



I come now to the most remarkable of Mr Lassell's disco- 

 veries, one of the most remarkable, indeed, as an insulated 

 fact, which has occurred in modern astronomy ; though, in- 

 deed, it can hardly be regarded as an insulated fact, when 

 considered in all its relations. 1 need hardly say that I al- 

 lude to the discovery of an eighth satellite of Saturn, a dis- 

 covery the history of which is, in the highest degree, credi- 

 table, not only to the increased power of the instruments 



