June 29, 1893] 



NATURE 



209 



and the position of the apex of the direction of motion has been 

 deduced by analysing the proper motions of the stars. A new 



[ determination on different lines (a spectroscopic method) appears 

 in the Astronomical Journal (No. 298), and in this Mr. A. D. 

 Risteen, the writer, bases his method on the three assumptions 

 (I) that the stars used in the computation have no tendency to 

 drift in any particular direction ; (2) that their absolute veloci- 

 ties do not depend upon their apparent positions in the heavens ; 



\, (3) that their absolute velocities are not functions of their own 



I directions. Another minor assumption is that the absolute 

 velocity of a star is not a (unction of the star's brightness. The 



; values he gets for the right ascension and declination are given 

 in the following table, in which we include those of Bischoff, 

 Ubaghs, L. Struve, and Stumpe. 



Decl. 



+ 48-5 

 266 



27'3 

 36-2 

 45-0 



The value Risteen obtains shows that the method may prove 

 a very valuable one in future when more stars can be included 

 ' (here about 42 observation equations are used), and the result 

 ■ he obtains shows that at any rate the reality of the sun's motion 

 (the value he gets is 109 English statute miles per second), and 

 that our present knowledge of the direction of this motion is 

 at any rate approximate. 



An Ascending Meteor. — Prof, von Niessl has been 

 investigating the path of the meteor that appeared on 

 July 7, 1892, and was seen both in Austria and Italy. The 

 result of this computation has shown that, undoubtedly, the 

 i path of the meteor at the latter end of its course {Naturwissen- 

 I schaftliche Wochenschrift, No. 26) was directed upwards. The 

 length of its path measured irco kilometres from its nearest 

 approach to the earth surface (68 kilometres above the surface) 

 to the point where it disappeared, which was at a height of 158 

 kilometres. This is about the first time that the path of a rising 

 meteor has been so accurately investigated. 



The Satellites of Jupiter.— In this column for March 30 

 of this year we referred briefly to the very important results that 

 were being reaped by Prof. W. H. Pickering, with the help of 

 Mr. Douglas, at Arequipa, with reference to the peculiar forms 

 ' which the satellites were found to assume at different periods of 

 their rotation. In the June number of Astronomy and Astro- 

 ph vsics we have before us a much more detailed account of these 

 and later observations, which seem to have confirmed those 

 made previously in nearly all respects. In this article, which is 

 > of some length, the author deals first with the third satellite, 

 the largest and most easily observed of the group. The results 

 of twelve series of observations, taken on seven different nights, 

 each series consisting of six independent observations, gave the ; 

 value of -10° -5 for the position angle of the major axis, the 

 satellite being on the eastern side of its orbit, and presenting an 

 elliptical disc. The observations for the elliptical phase at the 

 western side were not very satisfactory, owing to bad meteoro- 

 logical conditions, but the results suggested that " they would 

 imply a revolution of the axis about the line perpendicular to 

 ,the orbital plane, in about the same period as the satellites' rota- 

 tion upon the axis itself." With regard to the surface features, 

 "there seems to be a marking having the appearance of a fork, 

 the angle of the prongs varying from 30° to 60°. Sometimes 

 this forked-shaped feature is turned to the left and sometimes to 

 the right, and occasionally a double fork is seen. The position 

 langle of the axis of the belt gave a value of -h j 5''-5, and when 

 the values obtained on January i and 16 are compared with 

 those attained for the major axis on the same dates, they indi- 

 'cate that the two axis are inclined at between 46° to 35" to one 

 -mother. The attempt to determine the direction and period of 

 'rotation indicated that perhaps the period of rotation coincided 

 .vith that of the revolution of the satellite in its orbit. The 

 ■mrface features on the first satellite consisted of the bands lying 

 In an approximately north and south direction, that on the 

 second of a small patch detected only upon one occasion, and 

 hat on the fourth of a broad band (sometimes a narrow line), 

 md also a bright spot recorded several times at the North Pole 

 md once near the south. Later determinations of the period of 

 ■otation of the second satellite confirmed the earlier value (4ih. 

 Hm.), but sometimes discrepancies in the time of the flattening 

 >f the disc still occurred. The direction and period of rotation 



of satellite 4 has not been determined, but its disc has been 

 recorded upon fourteen different dates as being shortened in the 

 direction of the plane of its orbit, and upon eleven other days as 

 being circular in form. 



After summing up the main facts with regard to these satel- 

 lites respecting their small density, directions of rotation, 

 changes of shape, &c.. Prof. Pickering shows h:iw Laplace's 

 " ring theory" with the following premises, suits the facts : — 



(') Jupiter was formerly surrounded by a series of rings simi- 

 lar to those now surrounding Saturn. 



(2) The direction of rotation of these rings was direct, like 

 that of the planet. 



(3) By some force, whose cause is not explained, they were 

 shattered, their components uniting, but still retaining the same 

 orbit. 



(4) Like the original rings, each satellite still consists of a 

 swarm of meteorites, their consolidation having been prevented 

 by the enormous tides produced in them by their primary. 



At the conclusion of this discussion, in which Prof. Pickering 

 takes each point individually, he has drawn up a syllabus re- 

 garding the points to which an observer can he most profitably 

 directed in the case of each satellite, subdividing them into 

 grades according to the difficulty of the observations. 



TURACIN: A REMARKABLE ANIMAL PIG- 

 MENT CONTAINING COPPER.^ 



'X'HE study of natural colouring matters is at once peculiarly 



-"■ fascinating and peculiarly difficult. The nature of the 

 colouring matters in animals and plants, and even in some 

 minerals (ruby, sapphire, emerald, and amethyst, for example) 

 is still, in the majority of cases, not completely fathomed. 



Animal pigments are generally less easily extracted and are 

 more complex than those of plants. They appear invariably to 

 contain nitrogen — an observation in accord with the compara- 

 tive richness in that element of animal cells and their contents. 

 Then, too, much of the colouration of animals, being due to 

 microscopic structure, and therefore having a mechanical and 

 not a pigmentary origin, diflTers essentially from the colouration 

 of plants. Those animal colours which are primarily due to 

 structure do, however, involve the presence of a dark pigment 

 — brown or black — which acts at once as a foil and as an ab- 

 sorbent of those incident rays which are not reflected. 



Many spectroscopic examinations of animal pigments have 

 been made. Except in the case of blood and bile pigments very 

 few have been submitted to exhaustive chemical study. Spectral 

 analysis, when uncontrolled by chemical, and when the influence 

 of the solvent employed is not taken into account, is very likely to 

 mislead the investigator. And, unfortunately, the non-crystalline 

 character of many animal pigments, and the difficulty of purify- 

 ing them by means of the formation of salts and of separations 

 by the use of appropriate solvents, oppose serious obstacles to 

 their elucidation. Of blood-red or hjemoglobin it cannot be 

 said that we know the centesimal composition, much less its 

 molecular weight. Evenof h^^matin the empirical formula has 

 not yet been firmly established. The group of black and brown 

 pigments to which the various melanins belong still await ade- 

 quate investigation. We know they contain nitrogen (8i to 13 

 per cent.), and sometimes iron, but the analytical results do not 

 warrant the suggestion of empirical formulae for them. The more 

 nearly they appear to approach purity, the freer the majority of 

 them seem from any fixed constituent such as iron or other 

 metal. It is to be regretted that Dr. Krukenberg, to whom we 

 are indebted for much valuable work on several pigments 

 extracted from feathers, has not submitted the interesting sub- 

 stances he has described to quantitative chemical analysis. 



I must not, however, dwell further upon these preliminary 

 matters. I have introduced them mainly in order to indicate how 

 little precise information has yet been gathered as to the con- 

 stitution of the greater number of animal pigments, and how 

 difficult is their study. 



And now let me draw your attention to a pigment which I 

 had the good fortune to discover, and to the investigation of 

 which I have devoted I am afraid to say how many years. 



It was so long ago as the year 1866 that the solubility in 

 water of the red colouring matter in the wing-feathers of a 

 plantain-eater was pointed out to me. [One of these feathers, 



1 A discourse delivered at tlie Royal Institution by Prof. A. H. Church, 

 F.R.S. 



NO. 1235, VOL. 48] 



