June 1. 1899.] 



KNOWLEDGE. 



131 



and flintg in limestone are as fully paeudomorphs as are the 

 massive iron carbonates of Cleveland, or the silicified tree- 

 stems forming at the present day. 



Why some deposits contain flints and few traces of 

 siliceous organisms, while others are rich in such 

 organisms and contain no flints, is a question that has 

 been raised, and which is still imder discussion. The 

 preservation of spicules may possibly, as Mr. Jukes- 

 Browne* suggests, have been determined by the depth at 

 which the bed was formed, solution going on under pressure 

 in deep-sea deposits before the beds had actually consoli- 

 dated. M. Lucien Cayeux, I however, leaves the matter 

 very open. He concludes that " calcareous deposits of the 

 same origuial chemical and organic composition give rise 

 in course of time to three very different beds. The first 

 preserves its silica disseminated throughout the rock ; the 

 second becomes an almost pure limestone with abundant 

 flints ; the third passes into the condition of a pure lime- 

 stone without flints." 



In the last case, as in the Upper Jurassic of the 

 Mediterranean area, a rock maybe full of casts of siliceous 

 sponges and radiolaria, and yet the silica may be entirely 

 withdrawn. 



Has it not gone to form flint elsewhere '? Even in this 

 indirect fashion, the humble organisms, which are always 

 the most potent, may still be the makers of flint in 

 some other portion of the crust. 



A NEW SATELLITE OF SATURN. 



NEARLY all the astronomical discoveries made by 

 the aid of photography have related to the fixed 

 stars. In the study of the members of the solar 

 system, the results obtained by the eye are generally 

 better than those derived from a photograph. 

 For many years it has been supposed that photography 

 might be used for the discovery of new satellites, and in 

 April, 1888, a careful study of the vicinity of the outer 

 planets was made by Prof. William H. Pickering. Photo- 

 graphs were taken with the thirteen-inch Boyden telescope, 

 with exposures of about one hour, and images were obtained 

 of all the satellites of Saturn then known, except Mimas, 

 whose light is obscured by that of its primary. It was 

 then shown that Saturn probably had no satellite, as yet 

 undiscovered, revolving iu an orbit outside of that of 

 Enceladus, unless it was more than a magnitude fainter 

 than Hyperion. (Forty-third Report, p. 8.) 



In planning the Bruce photographic telescope, a search 

 for distant and faint satellites was regarded as an important 

 part of its work, and, accordingly, plates for this purpose 

 were taken at Arequipa, by Dr. Stewart. A carefal 

 examination of these plates has been made by Prof. 

 Wilham II. Pickering, and by superposing two of them, 

 A 3228 and A 3233, taken August lOth and 18th, 1898, 

 with exposures of 120", a faint object was found which 

 appeared in different positions on the two plates. The 

 same object is shown on two other plates, A 3227 and 

 A 3230, taken August lOth and 17th, 1898, with exposures 

 of tiO" and 122"" respectively. The position is nearly the 

 same on the two plates taken August 16th, but on August 

 17th it followed this position 33", and was south 19", while 

 on August 18th it followed 72", south 13". Its motion 

 was direct, and less than that of Saturn, though nearly in 



* " The Amount of disseminated Silica in Chalk, considered in 

 relation to Flints," Geol. Mag., 1893, p. 545. 



f " Etude Micrographique des Terrains Sedimentaires," Mem, de 

 la Soc. Geol. du Nord, Tome IV., 2 (1897), p. 443. 



the same direction. It cannot, therefore, be an asteroid, 

 but must be either a satellite of Saturn or a more distant 

 outside planet. The proximity of Saturn renders the first 

 supposition much more probable. On August 17th, the 

 position angle from Saturn was 106°, and the distance 1480". 

 Assuming that it was at elongation, and that its orbit is 

 circular, its period would be four hundred days, or five 

 times that of lapetus. It was at first identified with a 

 very faint object found on plates taken in 1897, and the 

 period of seventeen months was derived from them. This 

 supposition has not been confirmed. 



Measurements of the positions of the images give 

 additional material for determining the form of the orbit. 

 The method of measurement is that described in the 

 Annals, Vol. XXVI., p. 236. The uncorrected positions of 

 the four images referred to the first plate of August 16th 

 as an origin, are for x, 0-0", -t-1'2", -I-33-6", and -f 71'8" ; 

 fory,0'0", -1-7", - 19-8", and -42-1" ; the corresponding 

 Greenwich mean times are 12* 16"", 14* IS", 12* .56™, and 

 13* 12°'. Correcting for the motion of Saturn, the relative 

 motion with reference to that body is in .'•, 0-0", — 2'4", 

 -10-7", and -22-0"; in y, 0-0", -I- 0-1", -|- 2-4", and -f- 2-9". 

 It appears from this that the apparent motion is about 

 10-4" a day, at a distance of 1480". A computation shows 

 that if the orbit is circular, the period must be either four 

 thousand two hundred or four hundred and ninety days, 

 according as the satellite is near coujimction or elongation. 

 These values may be greatly altered if the orbit is elliptical. 

 Since the interval of time between the first and last photo- 

 graphs on which the satellite appears is only two days, it 

 is impossible to predict its position with accuracy. It is 

 probable that its position angle from Saturn now lies 

 between 280° and 290°, and its distance between 20' and 30'. 

 These uncertainties will probably be greatly diminished 

 from measures of plates of Saturn taken in Arequipa 

 on September 15th, 16th, and 17th, 1898, which for 

 some unexplained reason have not yet been received in 

 Cambridge. 



The direction of the motion, which is nearly towards 

 Saturn, shows that the apparent orbit is a very elongated 

 ellipse, and that it lies nearly in the plane of the ecliptic. 

 Prof. Asaph Hall has pointed out that this is to be expected 

 in a body so distant from Satiu-n. The attraction of the 

 latter only slightly exceeds that of the Sun. Hyperion 

 appears as a conspicuous object on all four of the plates, 

 and the new satellite appears about a magnitude and a-half 

 fainter on each. The approximate magnitude is therefore 

 about 155. As seen from Saturn, it would appear as a 

 faint star of about the sixth magnitude. Assuming that 

 its reflecting power is the same as that of Titan, its 

 diameter would be about, two hundred miles. It will, 

 therefore, be noticed that while it is probably the faintest 

 body yet found in the solar system, it is also the largest 

 discovered since the inner satellites of Uranus in 1851. 

 The last discovery of a satellite of Saturn was made in 

 September, 1848, by Prof. William C. Bond, then Director 

 of this Observatory, and his son. Prof. George P. Bond. 

 The satellite Hyperion was seen by the son on September 

 16th and 18th, but its true character was first recognized 

 on September 19th, when its position was measured by 

 both father and son {see Annals, II., p. 12). Soon after, it 

 was discovered independently by Lassell, at Liverpool. 



Prof. William H. Pickering, as the discoverer, suggests 

 that the name Phcebe, a sister of Saturn, be given to the 

 new satellite. Three of the satellites, Tethys, Dione, and 

 Rhea have already been named for Saturn's sisters, and 

 two, Hyperion and lapetus, for his brothers. 



Edwabd C. Piokbbing. 

 AprU 10th, 1899. 



