6o 



SCIENCE- G OS SIP. 



that can be revealed. In size he ranks amongst the 

 giant globes, for his diameter is not less than 75,000 

 miles, so that no less than 848 globes the size of 

 the Earth would only build up one such world. So 

 light, however, are the materials forming it that 

 only 94 globes like the Earth would be required to 

 balance Saturn. Indeed, were it possible to roll it 

 into a mighty sea of water, it would float like a 

 great hollow ball of wood. If a stone be dropped 

 on the Earth, it would fall 16 feet in one seconcl of 

 time ; taken to Jupiter, so great would be the increase 

 in the attractive power, it would drop 41 feet in the 

 same time ; but removed to the surface of Saturn 

 it would only fall 18 feet in a second. Thus we 

 may readily understand a very different condition 

 of things exists there from that around us. 



With a telescope of less than 2 inches aperture, 

 and a power of about 100, traces of belts may be 

 detected on the planet, a bright equatorial zone 

 being readily seen, and a dark shading on either 

 side extending to the poles. 



Larger apertures will show traces of belts in this 

 shading, usually one, or more frequently two, 

 parallel, edging the zone, whilst large instruments 



The ball is not placed centrally in the midst of 

 the rings, but a little to the west of the centre, 

 and it is probable that the observers at the Roman 

 observatory in 1842 and 1843 were quite accurate 

 in considering that the amount of the eccentricity 

 was rapidly variable. It may be readily seen with 

 small telescopes. I noticed it repeatedly in 1876 

 with a fine 2|--inch Browning Achromatic, with a 

 power of 132. The spectrum of Saturn has been 

 found by Sir W. Huggins to be very similar to that 

 of Jupiter, and, like it, undoubtedly showing 

 aqueous vapour. Jupiter is decidedly brightest in 

 the central portions of the disc, but G. P. Bond 

 considered the edges of Saturn's disc to be 

 brighter than the central portions, and Chacornac, 

 from the appearance of Titan when in transit on 

 May 1st, 1862, had ocular demonstration of the 

 fact. 



The most puzzling point about Saturn is un- 

 doubtedly the great ring system, which at its first 

 discovery, when the true nature was entirely un- 

 known, filled Galileo with wonder, making him 

 think he had discovered a triple globe. Nearly 

 fifty years elapsed before Huyghens came to 



Saturn, July 2, 1877. F. 0. D. 



will sometimes show a belt forming a ring round 

 the pole. The equator of Saturn is not in the 

 same plane as the ecliptic, but inclined at an angle 

 of over 28°, the effect being that in most portions 

 of his orbit one or other of his poles is tipped 

 towards the Earth. There are occasionally spots 

 on Saturn visible with large instruments, as will 

 be seen near the centre of the torrid zone in M. E. A. 

 Antoniadi's drawing. When these have been 

 watched the planet has been found to have a 

 rotation period of 10 hr. 14 min. 24 sec. The effect 

 of the quick rotation period, and the slight density 

 of the planet, has been to produce even greater 

 flattening at the poles than is seen in the case of 

 Jupiter, for when the planet is turned with its 

 rings edgeway, as seen from the Earth, the polar 

 diameter is found to be nearly one-ninth shorter 

 than the equatorial, and the astronomers Bond, 

 father and son, thought one of the poles more 

 compressed, whilst Sir W. Herschel and others 

 have sometimes fancied that there was also 

 a flattening around the equator, producing what is 

 known as a " square-shouldered " aspect. This 

 last appearance was probably an illusion, brought 

 about by the rings, which make it rather difficult 

 to be really sure of the actual figure of the ball. 



the conclusion that it must be a large flat 

 ring surrounding the planet. From the fact 

 that the rings are practically in the same 

 plane with Saturn's equator, and the equator in- 

 clined, as already mentioned, to the plane of the 

 ecliptic, for nearly fifteen years we see the top side 

 of the rings, and for a similar period the under- 

 neath side. At the time of the change from north 

 to south, or vice versa, for a short period, the ring- 

 is entirely lost to view, and for some time appears 

 but as a line of light. Under these conditions 

 Firmstone, in 1862, with a 2|-inch achromatic 

 lost sight of the ring four days earlier than Lassell. 

 with his 24-inch mirror, and caught it again only 

 three days after that observer. Secchi at Rome in 

 this year never quite lost the line of light, and the 

 12|-inch Merz Achromatic at Greenwich showed 

 it as a broken line. Large apertures will at these 

 times show a bright line crossing the planet at 

 times between the shadow of the ring and the 

 dark under side of the ring which is towards as, 

 the Sun shining on the other. When the dark side 

 is thus turned a little towards us Dawes saw traces 

 of a deep coppery tinge, but Huggins thought it 

 dark blue. 



{To be continued.) 



