5 88 



NATURE 



[Oct. 18, 1883 



theory seems to me to be natural, and to accord with facts all 

 round, but still it may be wrong. Those, however, who would 

 assign all elevation and subsidence to secular cooling and tan- 

 gential thrusts through shrinkage are revelling in their own 

 imaginations, for there is no reason why the earth's nucleus 

 should not have cooled as evenly as a cannon ball or piece of 

 pottery, or other homogeneous body ; and the records of the 

 Palaeozoic rocks, when we may suppose shrinkage would be 

 more active, certainly show Jthat its surface was then relatively 

 level, and without deep seas or great elevations on land. 



J. Starkie Gardner 



P.S. — A good example of subsidence may be seen in the 

 Tilbury Dock works in progress. So far as I could see, 

 Thames mud is being cut through to a depth of some ninety feet, 

 the upper part at least being filled with debris of reeds inter - 

 stratified with peaty matter or decayed reeds massed together. 

 The whole must have been deposited at or near high- water level, 

 and so recently that at thirty feet depth the decayed vegetable 

 matter still smells offensive. 



The Apparent Disappearance of Jupiter's Satellites on 

 October 14 



Rain fell without intermission on the afternoon and evening 

 of October 14, but at Ilh. it ceased and the clouds broke, 

 later in the night the sky cleared, but there were showers at 

 short intervals. 



At 1 5h. 15m. I observed Jupiter with a 10-inch reflector, power 

 about 212, and saw that the third satellite was the only one 

 visible. It was situated close to the east limb, and its disk 

 appeared somewhat faint, as if much clouded over with spots. 



1 5h. 55m. — The third satellite is entering upon the planet's 

 disk at a point in the same latitude as the upper side of the 

 great south equatorial belt. The fourth satellite is also seen 

 coming off the west limb. It looks remarkably faint. At this 

 time the configuration of the planet was extremely interesting 

 with the two satellites hanging upon the limbs. 



16I1. om. — The fourth satellite appears to have completed its 

 egress, and is evidently much in advance of the time given in 

 the Nautical Almanac. 



l6h. 15m. — The first has now reappeared from occultation at 

 a paint in the same latitude as the north equatorial belt. This 

 bell is a far more prominent feature than during the last 

 oppisition. 



l6h. 19m. —A large white patch on the planet's equator is 

 crossing the central meridian. On its north side the equatorial 

 belt is very dark. 



i6h. 30UI. — The third satellite is visible as a very dark spot 

 led upon the south equatorial belt, which is the darkest 

 belt upon the planet. 



17I1. om. — The second satellite is seen as a bright spot on the 

 interi jr margin of the west limb, and will shortly begin its egress. 

 It has crossed Tupiter in a latitude corresponding with the equa- 

 torial edge of the great south belt. The third satellite is now 

 perceptible as a black spot pursuing its course along the south 

 belt. The chief condensation of shading apparently lies on the 

 south side of the satellite, but the telescopic image is not 

 satisfactory. 



The disappearance of the satellites on this occasion can hardly 

 be said to have been complete, for at no time were they all in- 

 cluded within the margin of Jupiter. While the third entered 



11 1 1 disk the fourth released itself, and the two formed a 



curious configuration hanging upon the limbs. The third and 

 fourth satellites were extremely faint when clear of the di-k, and 

 their surfaces are evidently very feebly reflective compared with 

 that of their primary. It is significant that the third, though pro- 

 jected upon the darkest belt of Jupiter, was visible as a black 

 spot. The fourth probably crossed the planet as ablack spot also, 

 though I made no attempt to distinguish it under this aspect, 

 owing to frequent interruptions by clouds and rain. 



Bristol, October 15 W. F. Denning 



Arithmetical Notation of Kinship 



It seems to me that the elegant arithmetical notation for 

 ancestors proposed by Mr. Galton in his recent letter to Nature 

 (September 6, p. 435) may be further simplified. The modifica- 

 tion consists in first counting the grade3 and then counting the 

 species of the grades, as shown in \he following diagram : — 



Origin. 

 /\ 



/ "\ 



/ \ 



1. Parents y/ \,„ 



/ \ / \ 



j. Grandparents ... // tn\. / \«l 



,.Gre M -, / \ \ / -\ \ 



grand- , f / '"\ /. m\ >r m jf \m 



parents. /I 1 J 4 i> 6 7 8 



&C &c. 



Thus mother of mother of father is of the 3rd grade and of 

 the 4th species, and may be denoted by 3, 4. Let </ denote any 

 grade and r any species, then q, r is a complete specification for 

 an ancestor. The rule for analysing such a specification is — 

 Divide r by 2, adding a unit when the dividend is odd, and 

 repeat the operation (q - 1) times ; then when r or a quotient is 

 odd, substitute father, and when even mother. 



Take, for example, 3, 5. We get 5, 3, 2, her.ee father of 

 father of mother. Take 5, 5, we get 5, 3, 2, 1, 1, hence 



If we compare together the ancestors of the same species 

 number, we shall find that they have all the figures the same 

 until we come to unity, and that the generic difference depends 

 on the number of unities. The truth of this may also be seen by 

 considering the mode of construction of the diagram. 



Mr. Gallon's 253 is, in this notation, 7, 126. Analysing we 

 get— 



126 63 32 16 8 4 2 



m / in in in m m 



The ancestor 7, 1 of my notition is 128 in his. The analysis of 

 the latter is — 



12S, 64, 32, 16, 8, 4, 2, 



while that of the former is evident by inspection, namely — 



I, I, I, 1, I, 1, 1. 



With the double notation we know that when we come to unity, 

 eacli of the following symbols must be /; and that when we 

 come to a power of 2, each of the following symbols must be m, 

 followed it may be by some _/*'s. 



Alexander Mackari.ane 

 4, Gladstone Terrace, Edinburgh 



A Green Sun 



In connection with the phenomenon recorded in your last 

 number (p. 575), the following extract from my journal (Sunday, 

 July 14, 1878), when just north of the Arctic Circle on board the 

 Jonas Lie, may be of some interest : — 



"To-night the suu sets in a sky as pure and cloudless as that 

 of yesterday ; but the colours are quite different. Now there is 

 no crimson, but in its place orange, yellow, and molten gold. 

 All this exquisite beauty of colour is limited to a particular part 

 of the sky, and that not the west, but the north. Yes, strange 

 as it may seem, the sun sets scarcely a single point from the 

 north, and rises again nearly in the same place, barely two points 

 apart. Some heights are lighted up with the glow, but for most 

 of the time all around, save in the bright, favoured north, is cloud- 

 less darkness and gloom ; which yet is not the darkness of night, 

 but a grim, stormy, vague gloom in broad daylight. The after- 

 glow that follows sunset dies out, and without any sensible inter- 

 val of time, revives nearly in the same place ; the colour 

 brightens, and some small streaks of clouds grow brighter and 

 brighter, until the sun— the green sun — appears. A distant 

 low range of rocks comes between us and its point of rising, and, 

 as we glide on, an opening between them shows us the sun, a bright 

 emerald, as pure and brilliant as ever gem that glistened ; again 

 we lose it, and again an opening shows it to us in its own golden 

 light ; and then once more it is the bright green : and now it 

 rises higher, clears the ridge, and is once more the golden orb. 

 This is what we saw, but another observer assures us that when 

 (irsl he saw it, the colour was a fiery red, which soon turned to 

 green. Probably an optical effect of what is called polarisation 

 of light, as these complementary colours seem to show." ( ' A 

 Long Day in Norway," published in The Month in 1S78-9.) 



Henry Bedford 



All Hallows College, Dublin, October 13 



