330 



NATURE 



{July 31, 1879 



been preserved, and how nearly it resembles the similar 

 parts of modern Foraminifcra. He thinks, however, that these 

 round and regularly branching forms are rather exceptional, 

 vfhich is a mistake ; though it is true that the sections of 

 the larger canals are often somewhat flattened, and that they 

 become . flat where they branch. They are also sometimes 

 altered by the vicinity of veinlets or fractures, or by minute 

 mineral segregations in the surrounding calcite, accidents to 

 ■which all similar structures in fossils are liable. Another 

 objection, not original with him, is derived from their unequal 

 dimensions. It is true that they are very unequal in size, but 

 there is some definiteness about this. They are larger in the 

 thicker and earlier formed layers, smaller or even wanting in 

 the thinner and more superficial. In some slices the thicker 

 trunks only are preserved, the slender branches having been 

 filled with dolomite or calcite. It is difficult, also, to obtain, 

 in any slice or any surface, the whole of a group of canals,' 

 Further, as I have shown, the thick canals sometimes give off 

 groups of very minute tubes from their sides, so that the coarser 

 and finer canals appear intermixed. These appearances are by 

 no means at variance with what we know in other organic 

 structures. Another objection is taken to the direction of the 

 canals, as not being transverse to the laminjc but oblique. 

 This, however, may be dismissed, since Moebius has of course 

 to admit that it is not unusual in modem Foraminifera. It may 

 be added that some of the appearances which puzzled Moebius, 

 and which are represented in his figures, evidently arise from 

 fractures displacing parts of groups of canals, and from the 

 apparently sudden truncation of these at points where the 

 serpentine filling gives place to calcite. It would also have 

 been well if he had studied the canal systems of those Stroma- 

 toporcE which have a secondary or supplemental skeleton, as 

 Ccenostrotna and Caunopora. 



4. A fatal defect in the mode of treatment pursued by 

 Moebius is that he regards each of the structures separately, 

 and does not sufficiently consider their cumulative force when 

 taken together. In this aspect, the ease of Eozijon may be jjre- 

 sented thus: (i) It occurs in certain layers of widely dis- 

 tributed limestones, evidently of aqueous origin, and on other 

 grounds presumably organic. (2) Its general form, lamina- 

 tion, and chambers, resemble those of the silurian Stroinatopora 

 and its allies, and of such modem sessile foraminifera as Caipen- 

 teria and Polytrema. (3) It shows under the microscope a 

 tubulated proper wall similar to that of the Nummulites, 

 though of even finer texture. (4) It shows also in the thicker 

 layers a secondary or supplemental skeleton with canals. (5) 

 These forms appear more or less perfectly in specimens miner- 

 alised with very different substances. (6) The structures of 

 Eoziion are of such generalised character as might be expected 

 in a very early Protozoan. (7) It has been found in various 

 parts of the world under very similar forms, and in beds 

 approximately of the same geological horizon. (8) It may be 

 added, though perhaps not as an argument, that the discovery 

 of Eozoon affords a rational mode of explaining the immense 

 development of limestones in the Laurentian age ; and on the 

 other hand that the various attempts which have been made to 

 account for the structures of Eozoon on other hypotheses than 

 that of organic origin have not been satisfactory to chemists or 

 mineralogists, as Dr. Hunt has very well shown. 



Prof. Moebius, in summing up the evidence, hints that 

 Dr. Carpenter and myself have leaned to a subjective treatment 

 of Eozoon, representing its structure in a somewhat idealised 

 manner. In answer to this it is necessary only to say that we 

 have given photographs, natvire-prints, and camera- tracings of 

 specimens actually in our possession. We have not thought it 

 desirable to figure the most imperfect or badly preserved speci- 

 mens, though we have taken pains to explain the nature and 

 causes of such defects. Of course, when attempts at restoration 

 have been made, these must be taken as to some extent conjec- 

 tural ; but so far as these have been attempted they have con- 

 sisted merely in the effort to eliminate the accidental conditions 

 of fossilised bodies, and to present the organism in its original 

 perfection. Such restorations are not to be taken as evidence, 

 but only as illustrations to enable the facts to be more easily 

 understood. It is to be observed, however, that in the study 

 of such fossils as Eoziion, the observer must expect that only a 

 small proportion of his specimens will show the structures with 

 any approach to perfection, and that comparison of many speci- 

 mens prepared in different ways may be necessary in order to 



* I have succeeded best in this by etching the surface of broken specimens. 



understand any particular feature. A single figure or a short 

 description may thus represent the results of days spent in the 

 field in collecting, of careful examination and selection of the 

 specimens, of the cutting of many slices in different directions, 

 and of much study of these with different powers and modes of 

 illumination. My own collection contains hundreds of pre- 

 parations oi' Eoziion, each of which represents perhaps hours 

 of labour and study, and each of which throws some light more 

 or less important on some feature of stmcture. The results of 

 labour of this kind are unfortunately very liable' to be regarded 

 as subjective rather than objective by those who arrive at con- 

 clusions in easier ways. 



Taken with the above cautions and explanations, the memoir 

 of Prof. Moebius may be regarded as an interesting and useful 

 illustration of the stractures of Eaoon, though from a point of 

 view somewhat too limited to be wholly satisfactory. 



THE COLOURS OF DOUBLE STARS 



TN a recent number of the Bitlldin de V Academic royale de Bel- 

 *■ gique, M. Niesten, of the Brussels Observatory, has pub- 

 lished some interesting details relating to the colours of double 

 stars, to which subject he has given special attention for a consi- 

 derable time past. When comparing the periodicity of solar 

 spots with the longitudes of planets in the ecliptic, Messrs. De 

 la Rue, Balfour Stewart, and Loewy had found that a distinct 

 connection exists between solar activity and the relative positions 

 of the different members of our planetary system. A long tim'.- 

 ago the attention of astronomers had already been drawn to the 

 fact that Wolf's sun-spot period of eleven years coincides witli 

 the period of Jupiter's revolution round the sun. Later on Prof. 

 Balfour Stewart pointed out that the coincidence of the perihelia 

 of Jupiter and Saturn, which occurs about every fifty-nine years, 

 corresponds to another one of Wolf's spot-periods. 



If, therefore, the relative positions of the planets with regar. 1 

 to the sun have some influence upon the activity of that luminary ^ 

 the question is justifiable whether on the other hand the influence 

 of the sun upon the planets might not be apparent through some 

 slight changes in their colour. There is no doubt that the colours 

 of the planets actually do change ; their brightness increases and 

 decreases according to their position near the perihelion or 

 aphelion. In the case of Jupiter changes of colour have been 

 repeatedly observed, and they seem to coincide with the sun-spov 

 periods. At the last opposition of Mars, when the planet was 

 near its perihelion, it seemed to be less ruddy than usual ; 

 Uranus, which was generally described as shining with pah; 

 bluish light, is now, when it is approaching its perihelion, re- 

 markable by its bright white lustre. 



These relations between the sun and the planets induced M 

 Niesten to search for similar relations among the double stars- 

 and specially to try to answer the question whether the change.-, 

 of colour which have taken place in several double-star system-; 

 are in any way connected with the relative position of the com- 

 ponents of a double star. For this purpose he collected the ob- 

 servations of astronomers who have given special attention to 

 the colours of stars, and catalogued the colours of the stars 

 visible in our horizon. It was found that many double-stars 

 have not changed in colour since they were first obser\'ed, while 

 others in a period of more or less considerable duration havt- 

 shown a series of changes of colour, which seem to follow n 

 definite law. The changes of colour were particularly remark- 

 able in those double stars which possess great velocity of revolu- 

 tion. M. Niesten gives a table in which the different colours ot 

 twenty double stars of known period and periastrium, i.e., the 

 colours of the principal star and of the companion, as observed 

 at different periods, are compiled. From M. Niesten's discus- 

 sion of the facts revealed by this table, we will give that relating 

 to the first two double-star systems by way of example. 



In 70 / Ophiuchi, the period of revolution of which is 94'37 

 years, and for which the periastrium occurred in 1807, the colour 

 of the principal star at Herschel's time (an epoch closely preced- 

 ing the periastrium) was white ; the star then changed in colour, 

 passing from white, through yellow and pale topaz-coloured to 

 golden yellow, reaching this tint about 1854. From this period 

 it showed a tendency to return to white, passing through yellow 

 and pale yellow. In 1877 Mr. Pritchard designated it as pale 

 yellow, and afterwards as white. The companion during its 

 revolution showed similar fluctuations of colour to those of the 

 principal star. In the vicinity of the periastrium Herschel pu'. 

 it down as reddish (we must remember here that Herschel's 



