524 Royal Astronomical Society* 



the mean distances are the result of a small number of observations 

 calculated upon the gratuitous supposition of circular orbits. On 

 diminishing the radius of the second satellite by 0''"79, and aug- 

 menting that of the fourth by the same quantity, in order to make 

 the distances accord with the periods of revolution, the value of the 



mass of Uranus is found = ni^rr-, being less by one-fourth part 



than that obtained by M. Bouvard, from the perturbations produced 

 by the planet. 



Dr. Lamont remarks that, in giving this value he is too well 

 aware of the uncertainty of the data on which it rests to attach any 

 particular weight to it; but, though he considers the measures 

 obtained by him in 1837 as being unfit, until combined with fur- 

 ther observations, to give a value of the mass of Uranus that might, 

 with confidence, be employed in the theory of the planetary motion, 

 there is one purpose they will serve at present, namely, to enable us to 

 judge whether a given value of the mass of Uranus can be regarded 

 as probably true or not by its agreement or disagreement with them. 



Bouvard's value, which is generally adopted, is TtqTo* Computing 



from this the mean distances of the two satellites, the distance of 

 the planet from the earth being assumed = 19'223, he finds the 

 mean angular distance of the second satellite = 33"*96, and that 

 of the fourth = 45"*42. The difference of these values from those 

 computed from the observations, is + 2"- 61 and + 5"*35. Now, 

 without entering into the theory of probable errors, it will readily 

 be granted, he conceives, on considering the differences of the indi- 

 vidual errors from the mean, and even allowing a probable error for 

 eccentricity, that scarcely an error of 2", much less one exceeding 

 5", can be attributed to the distances obtained from observation. 

 The supposition of a constant error in the instrument can scarcely 

 be admitted ; for, on measuring distances that had otherwise been 

 determined with precision, no constant error has been found to 

 exist. 



In conclusion, the author states that he considers it certain that 

 the value of the mass of Uranus, at present used in the theory of the 

 planetary perturbations, ought to be greatly diminished, though the 

 precise proportion in which this should be done, cannot at present 

 be assigned. Considering the difficulty of the observations, and the 

 small number of nights in which measures of so much delicacy can 

 be made, it will not be possible, within the period of several years, 

 to deduce the true value of the planet's mass from the elongations 

 of the satellites. 



A table of these stars, giving the dates of observation, the desig- 

 nation of the objects, and the apparent right ascension for each Ob- 

 servatory, will be found in the Monthly Notices of the Society for 

 March. 



IV. Stars observed with the Moon at the Royal Observatories of 

 Greenwich and Edinburgh, and the Observatory of Cambridge, in 

 the months of October, November, and December, 1837. 



