December 29. 1892] 



NA TURE 



95 



His facts are;— Huggins finds the wave-length in the 

 Orion nebula as 5004.75, the magnesium fluting being 

 50o6'5, a difference of 175. At the same time, Huggins 

 finds very little, if any, sensible motion in the line of sight. 

 Mr. Keeler finds as a mean from 10 nebulae 5005-68, 

 magnesium being, according to his measurement, 

 5c)o6'36, a difference of "68. These latter observations 

 completely invalidate Huggins's evidence on this 

 point, especially as Mr. Keeler recognizes a motion 

 of recession for the Orion nebula of 107 miles per 

 second. 



Mr. Gore ought to have recorded the fact that in 

 Keeler's observations the comparisons for different nebulae 

 gave the magnesium sometimes more refrangible and 

 sometimes less refrangible than the nebular line. Later 

 observations of Keeler, "corrected for the earth's orbital 

 motion and the sun's motion,"give the nebular line a wave- 

 length of 5005*93, i.e. only "43 from the magnesium. 

 Assuming Keeler's latest results as perfectly correct, and 

 placing his position at Charing Cross, while representing 

 the position found for this line by Dr. Huggins in 1868 at 

 St. Paul's Cathedral, we find Dr. Huggins's limiting posi- 

 tions in 1889 as the extreme east and extreme west ends 

 of Green Park, his 1890 position in the middle of Green 

 Park, while the magnesium fluting will be at Cecil Street. 

 When we consider that a motion in the line of sight of 

 less than tweniy miles per second will make the nebular 

 line and the magnesium fluting absolutely coincident, that 

 the rate of the sun's motion in space is estimated but not 

 absolutely known, that these measurements are probably 

 the most difficult of all astronomical observations, and 

 that every increase of power and accuracy has brought 

 the lines closer together, we are certainly not justified 

 in stating that the " weight of evidence " is " against the 

 truth of the hypothesis." The differences in recorded 

 wave-lengths of well-known solar lines by experienced 

 observers are in many cases greater than the difference 

 in question here. 



Mr. Gore regards the dispersion used by Prof. Lockyer 

 as insufficient, and yet he records that sixteen prisms were 

 used by Loc .yer in some of his observations of the co- 

 incidence of the nebular line with magnesium, so that 

 hisdis|)ersion was actually greater than that used by Dr. 

 Huggins, and two-thirds that of Mr. Keeler, whose 

 dispersion equalled twenty-four prisms. 



The objec tions to th^t portion of the meteoritic hypo- 

 thesis whi. h deals with the meteoritic origin of the lines 

 in the auroral spectrum do not in any way affect th*^ main 

 hypothesis. That this subject is unimportant is distinctly 

 recognized by Prof Lockyer, " Meteoiitic Hypothesis," 

 p. 97, where he claims that ''certainly the coincidence is 

 such as to justify us in regarding meteoritic dust as the 

 origin of ihe spectrum until a belter and more probable 

 ori^^in is demonstrated." 



We aie told (p. 122) that Mr. Monck objects to 

 Lockyer's hypothesis, because it contains no explanation 

 of" why all the planets and asteroids and the great majority 

 of the s.itellites revolve in the same directum, why the 

 orbits of the larger bodies of the system deviate so little 

 from the circle and why they are so nearly in the same 

 plane." This wa> asked in 1890; and yet Prof. G. H. 

 Darwin had in 1888 shown that a swarm of meteorites 

 which, on the meteoritic l.ypothesis would form a nebula, 

 NO. 1 209, VOL. 47J 



may be considered as a gas, and therefore any answer 

 that the nebular hypothesis can give to these questions 

 will also apply to the meteoritic hypothesis. 



Such puerile sugge-.tions as that the meteorites used 

 by Prof. Lockyer " may have been " of terrestrial origin : 

 " that meteor clouds dense enough to produce the requi- 

 site amount of light by their collisions woul I also be 

 dense enough to intercept a great part of it again on its 

 way to the earth" (the italics are ours) ; and objections 

 based on Mr. Monck's interpretation of Prof. Newton's 

 calculations, and on opinions to which Mr. Monck 

 '•''inclines" as to the origin of certain comets, are evi- 

 dence that Mr. Gore has not hesitated to avail .himself of 

 anything that in any way seems to dsigree with the 

 meteoritic hypothesis. The whole of the " objections" 

 of the " opponents " of Prof. Lockyer recorded by Mr. 

 Gore are on matters of secondary importance, and 

 have been insisted upon by him owing to his complete 

 misconception of the theory. As a guide to the meteoritic 

 hypothesis his chapter is misleading, and utterly valueless 

 either as exposition or as criticism. 



After his account of the meteoritic hypothesis Mr. 

 Gore abruptly turns to a comparison of the various 

 drawings that have been made of the Milky Way, and 

 gives an interesting and valuable sum'nary of the present 

 state of our knowledge as to star distribution and move- 

 ment and the construction of the Universe. For this 

 portion of the book we have nothing but praise. It is 

 carefully written and copiously illustrated. Mr. Gore has 

 evidently taken the word " visible" in its widest possible 

 sense, for he includes not only things visible to the retina 

 of the eye, but those visible to the retina of the camera ; 

 and six excellent reproductions of photographs of nebulae 

 and stars clearly demonstrate the superiority of the latter 

 for astronomical purposes. It is probable that the use of 

 photography in the preparation of complete charts of the 

 Milky Way will throw much new light upon many of the 

 points discussed in this portion of the book, and may 

 profoundly modify many of the views at present held ; 

 but in presenting a clear and concise account of the 

 present state of our knowledge Mr. Gore has made a 

 valuable addition to the literature of ihe subject. An 

 appendix, in which are given various calculations and 

 tables involved in the discussion of several points raised 

 in the book, and a useful index, complete the volume. 



A. Taylor. 



THE IRON MANUFACTURE IN AMERICA. 



On the American Iron Trade and its Progress during 

 Sixteen Years. By Sir Lowthian Hell, F.R.S. 

 (Edinburgh and London : Ballaniyne, Hanson, and 

 Co.) 



IT is impossible, in the limited space at our disposal, 

 adequately to review this remarkable book, in which 

 no bram h of a very comprehensive subject appears to 

 have escaped the author's close atlentic»n. 



So full of detail and so exhaustive of the subject-matter 

 are the various sections into which the work is divided, 

 that we can do little more than glance at the numerous 

 subdivisions. 



The first section, dealing with international trade, dis- 



