Nov. 3, 1882.1 



• KNOAVLEDGE 



377 



throughout its navigable length is the almost untamable 

 cannibal tribes who inhabit the upper reaches between 

 Stanley's furthest point and the neighbourhood of Nyangine. 



J^fbi'fhJEf. 



PLAIX WAYS IN SCIENCE. 



MR WILLIAMS says he is not aware that the 

 reprint of his scattered essajs demands any apology. 

 Evidently he is not aware that Air. Christie, the Astro- 

 nomer-Royal, considers there is " no practice more repre- 

 hensible," and that an anonymous writer in the Atlantic 

 MoiUhhj (afterwards identified as Mr. Edward Holden, 

 then of the Washington Obser\atory, now cliief of the 

 Ann Arbor Observatory, Michigan) compares this habit to 

 highway robbery. For my own part, I share Mr. Wil- 

 liams's opinion ; nay, I go a little further, considering that 

 essays which will not bear reprinting were probably not 

 worth writing. As for the time of making such reprints, 

 surely, as Mr. Williams says, they are likely to be much 

 better done by the author himself than by his friends after 

 his death. 



The volume before us is full of interesting matter. Mr. 

 Williams has not a particle of respect for mere authority, 

 so there is no lack of novelty in his views. Some of his new 

 theories are open to exception ; but they are all well worth 

 considering. I had marked a number of the essays in the 

 present volume for notice as interesting and valuable ; but 

 have finally decided to speak only of the theory or theories 

 advanced in Mr. Williams's " Fuel of the Sun," here con- 

 cisely presented in the opening essay (thirty-four pages in 

 length), and touched on in the second, a much shorter 

 paper, relating to Dr. Siemens's " Theory of the Sun." 



The new theory opens with the argument that Wollaston 

 was wrong in regarding the atmospheres of the earth and 

 other members of the solar system as limited. Mr. Williams 

 attaches great importance to this point, considering that if 

 he is right, all our standard treatises on pneumatics and 

 meteorology must be remodelled. I cannot, for my own 

 part, see why. I doubt very much whether Dr. Wollaston's 

 paper has ever been held to be of great importance, or 

 whether it has ever been regarded as demonstrated that the 

 planetary atmospheres are limited. Certainly the atomic 

 theory, as it has been maintained for many more years 

 than have passed since Mr. Williams's theory was ad- 

 vanced, is inconsistent with Woll.aston's opinion, and still 

 more obviously with the reasoning by which Wollaston 

 attempts to establish his opinion. The rather daring theory 

 of Le Sage as to the true cause of gravitation may be cited 

 as an illustration of what is undoubtedly the case, that 

 many before Mr. Williams have regarded interplanetary 

 and interstellar space as occupied by matter. 



As for the consequences of the opinion maintained by 

 Mr. Williams (most probably right), he is, I take it, quite 

 mistaken in supposing them to be of great importance. He 

 finds the objections urged against his views, and Dr. 

 Siemens's later ones, invalid when once the atmospheres of 

 the heavenly bodies are regarded as unlimited. I have 

 myself received more than one letter pointing out that this 

 is so. (Dr. Siemens himself is of course persu.aded that it 

 is.) But the argument is based on the mistaken idea 

 that because there is no definite limit to a planet's 



* Science in Short Chapters. By \V. Mattiku Williams, .\nthor 

 of tho "Fuolof the Sun," "Through Norway with a Kiiapflnck," 

 Ac. (Messrs. Chatto & Windus, liondon.) 



atmosphere (or if there is no such limit), the atmo- 

 sphere which at any instant envelopes a planet is freely 

 interchangeable with the interplanetary atmosphere. 

 But this would not be the case. Interchange could 

 only take place in accordance with dynamical laws, and 

 these would not permit of more than an infinitesimal inter- 

 change between the atmosphere immediately surrounding 

 a planet and the attenuated atmosphere beyond. Mr. 

 Williams recognises this as soon as he tries to set his per- 

 petual solar machine working. " The sun will carry its own 

 .special atmospheric matter with it, but it cannot carry the 

 whole of the interstellar medium. There must be a limit — 

 graduated, no doubt, but still a practical limit — at which 

 its own atmosphere will leave Tiehind, or pass through, the 

 general atmospheric matter." This admission, though con- 

 venient where it is made, carries death with it to Mr. 

 Williams's theory, for it leaves things practically as they 

 would be if Mr. Wollaston's theory were unquestioned. 



Mr. Williams conceives the sun as rushing along 

 through space, gathering in the atmosphere of space 

 as it goes, compressing that atmosphere with all the 

 energy with which a normally limited atmosphere would 

 be permanently compressed, and so by its gravitating 

 energy producing intense heat, instead of that merely 

 constant pressure which would naturally result in 

 the case of a constant atmosphere. But neither the 

 onward rush of the sun through space, nor that swaying 

 of the sun around the common centre of gravity of the 

 solar system, which Mr. Williams regards as an all-impor- 

 tant point in his theory, could produce any such eflect. If 

 we imagine the sun without his atmosphere, drawing that 

 atmosphere in from surrounding space, he would unques- 

 tionably, in drawing it in, produce all the heat in which 

 Mr. Williams believes. And that heat might be stowed 

 away, so to speak, in dissociating the aqueous vapour so 

 gathered in, to be presently distributed as the elements 

 recombined. But with that first ingathering of atmosphere 

 would be the end of this particular source of solar heat. 

 The heat thus stored could be given out, but no more, or 

 only so much more as corresponded to the exceedingly 

 slight interchange taking place at the outskirts of the 

 solar atmosphere. Mr. Williams speaks as if the whole 

 of the long cylinder of interstellar atmosphere actually 

 traversed by the sun were gathered in and compressed to 

 the full tension of the solar atmosphere. But this could 

 not happen. The sun would travel through that atmo- 

 sphere, losing from his own (and taking up from outside to 

 replace) only so much as friction at the outskirts of his 

 atmosphere would displace. 



If there could be any doubt, when the question is viewed 

 as a hydrodynamical problem, that this is so, it should be 

 removed by the consideration that were the processes 

 conceived by IVIr. Williams to take place, one side of the 

 sun would inevitably present an appearance dittering in 

 the most striking manner from that of the other side. On 

 the forward hemisphere, there would occur a constant 

 ingathering of so much atmosphere as, when compressed liy 

 solar attraction, would produce the heat which Mr. Williams's 

 theory requires. (For note that the mere atntf of compres- 

 sion does not cause heat, but only the forcible compression of 

 vaporous matter which had been uncompressed). All the heat 

 thus generated on one side would be used up in dissociating 

 the aqueous vapour of the atmosiihere so gathered up. On 

 the other liemisphere the converse process would be taking 

 place. The dissociated gases would tliero rise, would 

 combine, with intense emission of heat, and the products — 

 the cinders left after the solar firing— would bo flung 

 away in the wake of the advancing sun. (At least Mr. 

 Williams's theory requires that this should happen.) Now, 



