THE PLANET NEPTUNE. 39 



of a micrometer with illuminated wires. By a com- 

 bination of all the Cambridge observations, Mr. Bond 

 has deduced the time of revolution five days and twenty- 

 one hours. A discussion of the entire series of ob- 

 servations made by Mr. Lassell at Malta in 1852, gives 

 the period five days, twenty-one hours, two minutes and 

 forty-four seconds, and the motion of the satellite is 

 found to be retrograde. The radius of its orbit is seven- 

 teen seconds, which gives about 236,000 miles for the 

 distance of the satellite from the planet. The light of 

 the satellite is nearly equivalent to that of a star of the 

 fourteenth magnitude. It is always more brilliant in 

 the S. W. than in the N. E. part of its orbit, present- 

 ing, in this respect, a striking analogy with the outer 

 satellite of Saturn. In the former position, Mr. Lassell 

 found it easy to observe, in the latter, extremely diffi- 

 cult. 



AFPAEENT OKBIT OF THE SATELLITE OF NEPTUNB FOB 1852. 



The preceding results enable us to compute the mass 

 of Neptune, which is found to be TT }^ part of the sun. 



Mr. Bond states that he has at times been quite con- 

 fident of seeing a second satellite, but has never yet been 

 able to obtain successive measures of its distance from 

 the primary. Mr. Lassell also in August, 1850, sus- 



