196 



NA TURE 



\_yan. 1, 1! 



the 700th part of it) the internal gravity has varied, not in 

 the direct ratio of the distance, but in the inverse ratio of 

 the square of the distance from the centre, and that is 

 the state of things to-day. 



In this last case the method of rotation of a ring of 

 diffused matter entirely changes. Let us hasten to say 

 that this alteration does not hinder the ring from existing. 

 Saturn is the proof of it. 



But whilst, according to the law of gravity first in 

 operation, the linear velocity of revolution in these rings 

 increased with the distance ; according to the second, 

 this velocity on the contrary decreased in the ratio of the 

 square root of this distance. 



In the first case, when the ring will have degenerated 

 into a secondary system, that is to say, into a nebula with 

 exterior rings, and finally into a planet with its satellites, 

 the rotation of the planet and the revolution of the satel- 

 lites will be in the same direction as the movement of the 

 original ring, that is to say, the motion will be "direct." 

 In the second case the secondary system thus formed will 

 be retrograde. 1 



What are we to conclude from this ? It is evident that 

 the planets from Mercury to Saturn, included in the 

 central region, were formed according to the first law, 

 when the sun did not yet exist or had not acquired a 

 preponderating mass ; and that the planets included in 

 the exterior region, which was by far the larger, were 

 formed when the sun had already come into existence. 



If then it should be discovered that Venus had a satellite, 

 its motion would be direct. If a planet were discovered 

 outside Neptune, its rotation and that of its satellites 

 would be retrograde. Here we have at last arrived at a 

 conclusion of the greatest interest : the earth is much 

 older than the sun. If it were otherwise — if, as Laplace 

 would have said, its formation had been long after that 

 of the sun — all would have been changed in the aspect of 

 the skies : the stars would rise in the west and set in the 

 east ; the moon would have a retrograde motion, like the 

 satellites of Uranus and Neptune. Let us add that at 

 that time it was further from the centre than it is now ; 

 for when the matter which was outside the terrestrial 

 orbit had passed over it to be reunited in the interior to 

 orm the sun, as the attraction of the latter gradually 

 preponderated, the revolution of all the planets within 

 the orbit of Uranus was accelerated. These planets 

 approached the sun at the same time that their satellites 

 receded from them. 



Finally, the actual state was attained, with the stability 

 which characterises it, when the mass of the sun, having 

 become enormous, could attract nothing more from the 

 original nebulous matter, and had at last created around 

 itself an empty space. 



The universe has grown out of chaos, that is to say, 

 out of a mass of matter excessively rare, without shape, 

 occupying a vast space and moving in various directions, 

 in virtue of which this chaotic matter was divided into 

 separate masses. It is by the progressive condensation 

 of these masses of chaotic matter towards certain centres 



1 Laplace believed thai in the nebulous rings derived from the sun 

 (according to his hypothesis)— rings which will have belonged to the second 

 case as they would be exterior to the sun— the friction of different con- 

 centric layers would have had the same effect as what occurs in the atmo- 

 sphere of a planet, which ends in moving altogether with the C( 

 In this way the ring will have taken on the movement of the first form, that 

 is to say a rotation ; its outer marginal layers will have had a greater linear 

 speed than that of the layers nearer the centre, and its condensation will 

 have given place to satellites with direct motion It is easy to show that 

 this manner of looking is not altogether exact (in proof of this we can point to 

 the rings of Saturn). The layers of an atmosphere press on one another; 

 further, the external layers only resist by their inertia to the communica- 

 tion of the rotatory movement which tends to establish itself between the 

 central globe and the extreme layers of its atmosphere. But, in a nebuli us 

 ring, the concentric layers do not press one on the other as in an atmosphere. 

 for each one moves in virtue of its ov, , m the sun. 



Further, the retardation of the layers situated near the extreme edge as 

 compared with the interna! layers is not due to their inertia, but to the laws 

 of their motion. If then the reared in accordance 



with the hypothesis of our go all the planets would have 



revolved round the sun in the direct direction, but their rotations and then- 

 satellites would be retrograde. 



of attraction that the innumerable stars have been 

 formed. Their incandescence comes from the heat de- 

 veloped during the act of their formation. The amount 

 of their heat is limited ; they will end by being ex- 

 tinguished. 



Amongst all the systems, which are infinitely varied, 

 which have grown out of the condensation of this primary 

 chaos, the solar system may be regarded as a very special 

 case. The primary nebula which gave birth to it was 

 spherical and homogeneous. I n separating itself from other 

 portions it had carried with it traces of a slow whirling 

 movement. These motions were soon regulated, thanks 

 to that particular law of internal gravitation resulting 

 from its shape and its homogeneousness. Nebulous 

 rings were thus formed in the same plane long before the 

 appearance of a central condensation. They gave birth 

 to nebulous masses also moving in this plane, in the same 

 direction and in circular orbits, around their common 

 centre. 



The secondary systems formed in the same way into 

 these partial nebulae can be definitely separated into two 

 categories : those which preceded the formation of the 

 sun, revolving on their own axes in " direct " directions ; 

 whilst the secondary systems, the furthest otf, formed after 

 the sun, revolve in a retrograde direction. These strange 

 phenomena which are presented by our solar system, 

 are doubtless, by a rare exception in the universe, only the 

 natural consequences of the initial conditions and of the 

 laws of mechanics. 



BERZELIUS AND WuHLER 

 T'HE " Jugenderinnerungen eines Chemikers," which 

 *■ the late Prof. Wohler contributed to the Journal of 

 the German Chemical Society in 1875, contains a delight- 

 ful sketch of the personal relations in which the great 

 German chemist stood to his illustrious master ; and Dr. 

 Hofmann's account of WShler's life and works, published 

 in the same journal for 1882, serves to fill in the details 

 of the picture. The story of Wohler's visit to Stockholm, 

 of his intercourse with Berzelius, and of the influence 

 which it exerted on the development of his scientific life, 

 are now well known to chemists. 



All the papers left by Berzelius are in the possession ot 

 the Swedish Academy of Sciences at Stockholm, and 

 among them are the letters which he received from 

 Wohler. Sonic time before his death Wohler presented 

 his letters from Berzelius to the Academy with the injunc- 

 tion that they were not to be published before the close 

 of the present century. Some extracts from the letters of 

 Wohler, on the publication of which no restriction was 

 made, have recently been given to the world by Dr. Edv. 

 Hjelt of Helsingfors, 1 from which we may gather some 

 notion of the wealth of material which will be at the dis- 

 posal of him whose lot it is to write the personal history 

 of the chemistry of this century. 



Wohler's letters to Berzelius extend from 1823 to 1846, 

 and are 230 in number. In all probability the corre- 

 spondence was continued up to the time of Berzelius's 

 death in 1848, but the letters of the last two years are 

 not contained in the collection. The greater portion of 

 the letters from Wohler consist of accounts of his investi- 

 gations, of discussions of scientific questions, of critical 

 opinions on new works and new theories, and of memora- 

 bilia of the chemists of the time. Many of the letters 

 have reference to the translation of Berzelius's " Jahres- 

 berichten " and his large "Manual of Chemistry" into 

 ( 1 man. Now and again we have a gossiping letter, rich 

 in a quiet humour, and occasionally illustrated by quaint 

 characteristic sketches. First in order of time comes 

 Wohler's application for a place in Berzelius's laboratory, 

 dated July 17, 1S23, and next is his grateful acknowledg- 



1 "BruchstuckeausdenBriefenF. WBhlers an 1. [. Berzelius." Heraus- 

 gegebenvonDi Edt Hjelt. (Berlin : Robert Oppenheim, 1884.) 



