November, 1912. 



KNOWLEDGE. 



445 



impressions. First, that he is no mere armchair philosopher 

 who has " dabbled " in biology, but a practical zoologist with 

 firsthand knowledge of what he writes about. Secondly, that 

 he is a man of marked literary taste and ability, and thirdly. 

 that he has thought for himself on a philosophical subject 

 that has keenly interested biologists since the days of the 

 '■ Naturphilosophen." 



Mr. Huxley m his preface disarms criticism, for he points 

 out that his facts are true whether or no we agree with him 

 as to the particular meaning which he attaches to the philo- 

 sophical use of the word " individual," and it is to a most 

 interesting series of facts that he draws attention. The book 

 is so written that the educated layman will have little difliculty 

 in following the train of argument if he takes it seriously, 

 while the zoologist will doubtless learn new facts, the results 

 of research recently published, that have not yet found their 



way into the textbooks. Dogiel's discovery of a new group of 

 simple parasites, the Catenata, Woodruff s work on Piiraincic- 

 ciiiiit, and Newman and Paterson's remarkable account of 

 .Armadillo quadruplets, will assuredly be new to many who, 

 like the present writer, strive in vain to keep themselves 

 cm coil rant with discoveries in zoology, amidst a rush of 

 professional work. 



The first chapter will probably be found least easy to follow ; 

 but it must be grappled with if the author's point of view is to 

 be understood. The remaining ones are all more or less easy 

 reading. The illustrations call for no counnent ; but we could 

 wish that less use had been made of footnotes. It only 

 remains to be said that the book should have a wide sale, and 

 the author must be congr.atulated on the interesting and 

 stimulating manner in which he has put forth his conclusions 

 on some important points. 



SATURN, 



Bv FK.\NK C. I)EXXI:TT. 



Of all celestial objects Saturn stands alone as an example of 

 exquisite beauty. As an object for continuous study many 

 other bodies doubtless are of greater interest, either from 

 lower instrumental powers being of greater service, or from 

 constant physical happenings bringing continual change. But 

 as an object of beauty Saturn is unrivalled. The ball, some 

 seventy-five thousand miles in diameter, is marked, even more 

 regularly than Jupiter, with belts parallel with its equator. 

 Some of these are easily observable with a telescope so small 

 as two and a quarter inches in aperture. But to see the 

 whole, with the exquisite colours they display, will tax the 

 powers of the best instruments under the most favourable 

 conditions. The form of the globe is best seen when the 

 rings are presented edgeways. Apparently then one of the 

 poles is flattened rather more than the other. 



The ring system is the cause of the exceeding beauty. It 

 may well have puzzled the first observers with their inferior 

 instruments. Nowadays, seeing that we have some knowledge 

 of the nature of the object, even a two-inch achromatic 

 will give a pretty view, when the rings are widely open 

 as they are now. Every increase of aperture, however, 

 adds to the beauty. A two and a half inch to three inch 

 reveals the fact that the ring is divided into at least two 

 parts, an outer ring and an inner. This was first discovered 

 in 1675 by Cassini, hence the division is often known as 

 Cassini's. It was at one time called Ball's through a mistaken 

 interpretation of the writings of one of the brothers Ball. It 

 will be seen that the inner ring is brightest and fades inwards, 

 also that the outer ring is not evenly bright. A little increase 

 of aperture reveals the presence of the inner " crape veil," the 

 semi-transparent ring discovered simultaneously in England 

 and America by Dawes and Bond respectively, in 1850. That 

 it was in existence previously there can be no doubt, because 

 Cassini shows its form where it crosses the planet so far back 

 as 1715. Vet the Herschels and Schroeter with their giant 

 reflectors, and Struve with the 9-6 inch Dorpat achromatic 

 repeatedly studied the planet and missed it. In ISSO it could 

 not have well been overlooked even with .i four and a half- 

 inch reflector. 



The ring system presents many problems. In the first 

 place, the ball is not exactly in the middle of the rings, but 

 just a little to the west of the centre. This has been noted 

 even with quite small instruments. The Cas.sini division, too, 

 is not always equally dark. The outer ring has a division in 

 it known as Encke's, from his careful measures of its position. 

 The peculiarity of this diviMon is that on equally propitious 

 nights, and with the same instrument, the division is variable. 

 Sometimes it may be seen hard and sharp in one ansa, whilst 

 no trace of it can be found in the other. Sometimes the best 

 instruments fail to reveal it, whilst at others it is like a mere 

 pencil marking. Further, it is not a fixture, sometimes 



appearing nearer the inner edge, at others nearer the outer. 

 Occasionally it has appeared to be accompanied by other 

 still finer divisions. The middle ring usually seems simply to 

 fade inwards, but sometimes appears to be sensibly stepped, 

 and it has been observed apparently divided by at least three 

 narrow divisions. The inner dusky ring looks at times as if 

 in contact with its neighbour, at others, separated from it by 

 a division, whilst occasionally the " crape veil " has itself 

 seemed to be split by a division. 



Another mystery of the rings is that the outline of the 

 planet's shadow upon the rings has appeared not smooth, but 

 notched. The best explanation of this is to be found by 

 supposing that the rings are either not all of the same 

 thickness, or else — or perhaps also — that they are not all in 

 the same plane. This last suggestion is seemingly borne out 

 by the fact that at the last time when the rings were presented 

 edgeways they never quite disappeared even with a three-inch 

 achromatic, whilst with larger instruments they appeared as 

 bright knobs or beads. 



Were the ring-system solid it would not be stable as the 

 outer portions would be travelling at a much greater rate than 

 the inner. This would inevitably lead to disruption : the inner 

 portions travelling too slowly would be drawn downward upon 

 the planet, whilst outer parts travelling too rapidly would rush 

 oft" — away from the planet's control. Keeler's spectroscope 

 proved that the rings were not solid ; that the inner portions 

 w^ere travelling, in accordance with necessity, much faster 

 than the outer portions. The conseiiuence of this is that 

 there is a constant change of the particles with respect 

 to each other. This explains the irregular density 

 observed at the extremities of the curves from time 

 to time as seen with the largest instruments, and the 

 variations in the divisions. At present, November, 1912, 

 Saturn is in good position for observation, high up in the 

 heavens between the Pleiades and Aldebaran. Moreover, the 

 rings are at such an angle that the northern pole is hidden 

 behind the rings, whilst the southern one is apparently bedded 

 on them. Although Saturn is not so brilliant as Jupiter, it is 

 a remarkable fact that the same telescope can be used with 

 higher powers on the former than upon the latter with good 

 result. The five older known moons may be observed with 

 any telescope of about four inches in diameter; but they are 

 not so interesting as those of Jupiter, as their phenomena are 

 not so easily observed. Dual discovery was again shown 

 when Lassell,in England, and Bond. in America, simultaneously 

 found the tiny Hyperion in 184iS. This satellite, like the 

 oldest known, Khea, Dione, Titan, and lapetus, displays 

 variations in its brightness in difl"erent parts of its orbit, 

 variations which seem to indicate that, like our Moon and 

 some of Jupiter's, they always present the same face to their 

 primary. 



