102 HISTOEY OF ASTRONOMY. 



The intervals were so short as to enable him to identify 

 each satellite without danger of mistake. These sat- 

 ellites were the two brighter ones discovered by Her- 

 schel, and two interior ones, whose periods are about 

 two and four days respectively. 



In the autumn of 1852, Mr. Lassell transported his 

 telescope to the island of Malta, in the Mediterranean, 

 for the purpose of securing the advantage of a lower 

 latitude and a purer sky, and here he succeeded in obtain- 

 ing a very complete series of observations of the satellites 

 of Uranus. The nearest satellite was observed on 24 

 different nights ; the second satellite on 23 nights ; and 

 the two brighter satellites on 26 nights. By combining 

 these observations with those of 1847 and 1851, we are 

 able to assign the dimensions of their orbits and their 

 periods of revolution with great precision. The period 

 of the nearest satellite is 2.520345 days ; or 2d. 12h. 29m. 

 20s. 66. The period of the second satellite is 4.144537 

 days; or 4d. 3h. 28m. 8s. 00. 



From the combination of all the observations between 

 1787 and 1848, Mr. Adams has determined the period 

 of the third satellite to be 8d. 16h. 56m. 24s. 88 ; and in 

 the same manner he has determined the period of the 

 fourth satellite to be 13d. llh. 6m. 55s. 21. 



Let us now examine the observations of Sir William 

 Herschel, and see what light is shed upon them by the in- 

 formation recently obtained. There are four instances 

 in which he observed what he called "an interior 

 satellite." 



