1865.] Saturn and its System. 721 



too, directly opposed to the faith of the Catholic Church, should have 

 been a most determined enemy of his fellow-countryman and con- 

 temporary reformer in another field, Luther, against whom he signed 

 an edict issued in 1526. In the application of Kepler's third law to 

 the case of Saturn, the language is very obscure. This is the more 

 noticeable as obscurity is a rare fault throughout the work. Even 

 when the reasoning seems inconclusive the statements are clear. At 

 page 39, however, when inquiring into the relation between the num- 

 bers 9 - 53885, or Saturn's mean distance in terms of the mean distance 

 of the earth, and 29 • 4566 or his period in terms of the earth's period, 

 it is said " the first is less than the second, but the square of the first 

 is plainly greater than the square of the second " (than the second '?) 

 " We must therefore try higher powers of the second " (of the first ?) 

 " Trying the next power, that is, the square of the second, we imme- 

 diately find the relation we are seeking : — thus, the square of the first 

 number is less than the square of the second, but the next power or 

 cube is almost exactly equal to the square of the second." 



In July, 1610, Galileo began to examine Saturn with his largest 

 telescope, discovering as he thought that the planet was triform. 

 Examinations thus initiated led eventually to the discovery of the 

 three rings and eight satellites. As Mr. Proctor adopts as the basis 

 for a new theory on the nature of the rings, the grounds advanced by 

 M. Otto Struve, in 1851, in his work " Sur les Dimensions des 

 Anneaux de Saturne," in support of the hypothesis that the rings are 

 rapidly advancing towards, and will ere long be precipitated on to, 

 the globe, we shall devote a short space to an examination of the 

 validity of these premises. They are as follow : — Since the time of 

 Huygens, the width of the ring system, as determined by proportional 

 admeasurements, has been steadily increasing by the approach of its 

 inner edge to the globe ; the dark ring since November, 1850, the 

 date of its discovery, has itself been observed to increase considerably 

 in width. The breadth of the ring was found by Huygens to equal 

 that of the space between it and the globe. Herschel, 107 years later, 

 found the ratio between the width of the ring and the space to be as 

 5 : 4, while still later observers have found it to be yet greater. Do 

 these admeasurements form a sufficiently sound basis on which to rear 

 a novel hypothesis ? We think not. Before stating our reasons for 

 so thinking, we would remark a statement of the author's which seems 

 in itself sufficient to throw doubt on its soundness. He says that 

 Pound made the width of the system less than that of the dark space, 

 but that he selects Huygens's measurements as less favourable to his 

 case. But would Pound's measurements have favoured the case ? If 

 they had been made before Huygens's they might have been thought to 

 do so, but the truth is that they were made after his, and therefore on 

 the* supposition that both are equally reliable, they should be taken to 

 indicate a diminution in the breadth of the system between the two 

 periods of measurement — an occurrence which would militate against 

 that uniform increase in breadth on which the whole question rests.* 



* Huygens's measures were taken in 1657, Pound's in 1719. 



