302 



KNOWLEDGE & SCIENTIFIC NEWS. 



[Dec, 1904. 



[The credit belongs to Miss Plunket of having first pointed 

 out that the Hj'dra was clearly designed by the original 

 constellation makers to mark the equator celestial, and I 

 have no doubt that Miss Plunket's suggested reason is quite 

 correct, namely, that the ancients wished to mark by this 

 gre;it snake the part of the equator which was furthest below 

 the track of the sun. And it lay along the equator approxi- 

 mately both at the date she urges (4000 B.C.) and at that 

 which I put forward (2700 H.c). Nevertheless the earlier 

 date is inadmissible. The south pole of 4000 B.C. is too far 

 from the centre of the unmapped space in the southern 

 heavens for the work of constellation making to have been 

 completed by that epoch ; and, as I have elsewhere pointed 

 out, the traditional figures bear too manifest indications of 

 being items in a single plan for the work to have been done 

 piecemeal, or to have occupied several generations. The 

 earlier date would also displace Serpens and Scorpio from 

 their very significant relation to the colures. — E. W.\lter 

 Macndek.] 



The Cygnus " CoaLl=Sa.ck," 



To THE Editors of " Knowledge." 

 Bins, — In the Milky Way, a little north of the "Northern 

 Cross " — between the stars f and p Cygni, in fact — I have fre- 

 quently observed a black rift cutting the course of the Via 

 Lactea transversely. Do you mind explaining the nature of 

 this phenomenon ? 



The appearance does not seem to hv due to the presence of 

 a dark nebula, because very moderate telescopic aid reveals 

 faint stars in its recesses. 



Have we here a veritable opening in our island-universe — a 

 sort of tunnel through which we may peer into the sparsely- 

 lit infinity beyond ? 



"^'ours faithfully, 

 Alderwasley, nr. Wirksworth, J. B. Wallis. 



Derbyshire, 

 November 14, 1904. 

 [The rift to which Mr. Wallis draws attention is clearly shown 

 on Dr. C. Easton's charts of '• La Voie Lactee." The 

 phenomenon is doubtless of the same nature as the other 

 numerous rifts, channels, and gaps in the Milky Way ; they 

 cannot be due to the interposition of dark absorbing nebula:-, 

 but are evidently integral parts of the Galactic structure. — 

 E. Walte.r Maunder. 1 



The TeaLchirvg of tKe Principles 

 of Evolution in the Schools. 



To THE Editors of " Knowledge." 

 Sirs, — Over a quarter of a century ago Professor Virchow 

 said: "If the theory of descent is as certain as Professor 

 Haeckel thinks it is, then we must demand its admission into 

 the school, and this demand is a necessary one." I think the 

 time has arrived when all educationists should consider the 

 desirability of teaching children the principles of evolution. I 

 believe all the sects accept the evolution theory, and it would 

 not be difficult to present the facts in such away that children 

 could understand them. 



Yours faithfully, 



J. A. Keid. 

 Kincraig, Cutcliffe Grove, Bedford, 

 November 18, 1904. 



REVIEWS OF BOOKS. 



Earthquakes.— If it wore possible to find a peg for criticism 

 in so admirable a work as M.ijor C. E. Dutton's " Earthquakes 

 in the Light of the New Seismology" (John Murray), it would 

 not be in the book but in the fact that the first general digest 

 of the knowledge and views which are associated with the 



work and theories of Professor John Milne, Professor Ewing, 

 Professor Nagaoko, of Tokio, Major f)e Montessus de Ballore, 

 and Dr. Emil Rudolph, of Strassburg, should have been made 

 by an American rather than by an English man of science. 

 However, science is the true cosmopolitan influence, and it 

 behoves us to regard Major Dutton's able, patient, and 

 judicious examination of what the liest authorities think and 

 know of a subject which has a fascinating interest for all man- 

 kind, as an iustance of it. A happv distinction is made in 

 Major Dutton's introduction between the standpoint of the 

 new seismology and the old. The old view of earthquakes 

 was that they were one of those formative geologic forces, 

 almost as mysterious and axiomatic as the occurence of matter 

 ifself, which existed in order to bring about structural results. 

 The new view regards earthquakes as merely the effect of 

 geologic forces, just as thunder is an effect of the electric 

 discharge — not the cause of it. As a sound is the elastic 

 vibration of the air, so an earthquake is merely the elastic 

 vibration of the earth mass. Hence the science becomes 

 in a great measure the investigation of elastic wave 

 motion in a solid medium. That investigation became 

 possible with the invention of the seismograph, the earth- 

 tremor measurer; and the correlation of the results which the 

 seismograph afiorded was primarily the work of John Milne. 

 He has been followed by hosts of patient investigators in every 

 country of the world ; and Major Dutton's book is a summary of 

 the results and conclusions at which they have arrived. His 

 earlier chapters set forth the nature of earthquakes and dis- 

 cuss their double causation, \olcanic .and "stratagic," if we 

 may coin a word to replace the usual one of "tectonic." 

 Chapters descriptive of the instruments used are followed by 

 others which enter exhaustively into the character, charac- 

 teristics, and theoretic features of the various kinds of earth 

 tremors or waves which agitate the earth's mass and the 

 earth's crust. Chapter XIII. takes up the question of speed 

 of propagation, its connection with the relation of elasticity to 

 density; and the light which is consequently thrown on the 

 densities of the earth's interior at varying depths. The last 

 chapters indicate the general distribution of earthquakes, and 

 the index they afford of the points of origin of great seismic 

 disturbances, both on land and in the depths of the sea. The 

 volume is one of the most interesting which has appeared in 

 the " Progressive Science Series," and will appeal to a world- 

 wide audience. 



"The Mathematical Theory of Eclipses," by Koberdean 

 Buchanan, S.B. (J. B. Lippincott Company, Philadelphia 

 and London, 1904). This work is designed for the computer 

 of solar and lunar eclipses, and not for the use of the practical 

 observer. The author is eminently fitted for his task, as he 

 has been engaged for the last .;4 years on the computation of 

 eclipses for the American Ephemeris. The book is based on 

 Chauvenet's chapter on eclipses in his " Spherical and Prac- 

 tical Astronomy," but the great experience of Mr. Buchanan 

 has led him to sift out the unnecessary formula from the neces- 

 sary, and to arrange their order into a more convenient form 

 for computation. A graphic method is also employed for 

 explaining the formulee : — " The eclipse is dissected after the 

 manner of a surgeon — it is cut up and the hidden parts laid 

 open to view." Mr. Buchanan observed the total eclipse of 

 1900, May 28, at Newberry, South Carolina, where he gave 

 special attention to the shadow bands, and this feature is the 

 only observational one connected with eclipses with which he 

 treats. The cause of the shadow bands is still doubtful, but 

 Mr. Buchanan is inclined to attribute them to the undulations 

 and disturbances of the density of the atmosphere within the 

 core of the shadow, caused by the lower temperature of the 

 cone (which may fall by 4° or 5°), thus producing intermittent 

 opacity. He also explains the factor producing the " Black 

 Drop" in a transit of Venus or Mercury, and " Baily's Beads" 

 at the second and third contacts of the moon with the sun. He 

 also clearly disposes of the somewhat widely-spread idea that 

 the darkness at the Crucifixion was caused by an eclipse of 

 the sun ; this could not be, since a solar eclipse can only occur 

 at new moon, and the Feast of the Passover (upon the eve of 

 which the Crucifixion took place) was appointed by the law to 

 be held at the full moon of the first month. 



Chemical Enjiineering. — A second edition of Mr. George E. 

 Davis's " Handbook of Chemical Engineering " has been pub- 

 lished by Messrs. Davis Brothers, of Manchester, and the 



