September 1, 1891.] 



KNOWLEDGE 



171 



for atmospheric refraction, but 

 by Prof. Ames, we liave 



Places observed by 

 Ames, corrected 

 for atmospheric 

 refraction. 

 G5G-1-97 

 4862-93 

 4342-00 

 4103-11 

 3971-40 

 3890-3 

 3836-8 

 3799-2 

 3771-9 

 3751-3 

 3735-3 

 3722-8 

 3712-9 



about the proper correction 

 using the numbers adopted 



Places calculated 

 = 3647-20 J?^^ 



C 6564-96 



F 4862-93 

 Gi 4341-90 



h 4103-10 



H 3971-4 



a 3890-3 



fi 3886-7 



7 3799-2 



S 3771-9 



s 3751-4 



K 3735-6 



V, 3723-2 



5 3713-2 



The positions of the next three lines, t, k, and A, calculated 

 from Balmer's formula, are 3705-1, 3698-5, and 3692-9, 

 "which agrees very satisfactorily with the positions of the 

 lines shown on the photograxsh of the spectrum of Vega 

 given me by the Brothers Henry. 



We may, therefore, feel some confidence that Balmer's 

 formula corresponds to a physical fact, and that one series 

 of tremors with which the hydrogen molecule vibrates 

 when it is disturbed, are related so that the length of 

 the waves produced, when jjlotted as in the diagram, 

 fall upon a curve having an asymptote at wave-length 

 3647-20. 



If m be made equal to 1 in the formula, we get an 

 infinite value for A ; which indicates that there ought to 

 be one line of the series forming the limit of the spectrum 

 at the extreme red end. When m is made equal to 1, we 

 get A= — 1215-4. It would be interesting to determine 

 whether this negative value of the wave-length may be 

 interpreted as meaning a wave of opposite phase. If so, 

 we should expect to find a line of the series at wave-length 

 1215-4, a region of the spectrum which has not yet been 

 explored. 



Notices of Boolis. 



I'dimhir Ash-diKiiiiij : A svrii's <if l.n turfs ,li'liirn,l 'it 

 Ipsiriih by Sir George I'liddell Airy, K.C.B., Astronomer 

 Royal, revised by H. H. Turner, M.A., B.Sc, Chief Assist- 

 ant Royal Observatory, Greenwich. These lectures of Sir 

 G. B. Aii-y are a model of clear and simple ex]iosition. 

 They were delivered more than forty years ago (in March, 

 1847) to the members of the Ipswich Museum and tlicir 

 friends, and were, as Sir Cr. B. Airy explained at the time, 

 intended to be understood by working men. That he sue- 

 coeded in making the somewhat difficult and dry subjects 

 that he dealt with interesting is attested by the fact that 

 the book has passed through six editions, and that now a 

 seventh is called for. The instnuucnts used in observa- 

 tories have so changed since the date when the lectures 

 were delivered that Mr. Turner has had a difficult task in 

 making the necessary alterations in the text without sug- 

 gesting anachronisms or greatly altering the form in whieli 

 the lectures were delivered, but he has done his work with 

 great discretion, and has added some interesting notes. 

 Amongst the many "Popular Astronomies" which have 

 been written it would still be difficult to select a better 



book to give to young people whose interest in Astronomy 

 is dawning. 



Pictor'ud Astronoini/. By G. F. Chambers, F.R.A.S. — 

 Mr. Chambers has barely finished working upon his en- 

 larged edition of the " Descriptive Astronomy," when he 

 gives us another entirely new volume, intended for 

 beginners in Astronomy. It is profusely illustrated, and 

 contains a great deal of valuable information, with some 

 useful tables and practical suggestions for those who 

 meditate setting up a small observatory, but the drawings 

 of observatories and instruments are mostly of very old- 

 fashioned type. In fact all the illustrations are antiquated, 

 and we recognize most of them as old friends, which have 

 done yeoman's sernce in the teacliing of Astronomy. 

 But the strength of Mr. Chambers' books never lays in 

 their illustrations. 



Outlines of Field (ieoUniy. By Sir Akchibald Geikie, 

 F.R.S. Fourth edition. (Macmillan.) — Among the many 

 works of this distinguished author, few are more welcome 

 than this new and much enlarged edition of his well-known 

 " Field Geology." Two lectures upon geological maps and 

 instruments of surveying, delivered in 1876, and published 

 in pamphlet form in the same year, were the source from 

 which this book took its origin. In 1879 a second edition 

 appeared in a more permanent shape, so much enlarged 

 and re-cast as to constitute a new book, of which the 

 present edition is a still further improved form. As the 

 author says in the preface, his aim has been to write for 

 the large body of readers who, though possessing some 

 general acquaintance with Geology, find themselves helpless 

 when they try to interpret the facts which they meet with 

 in the field. Sir Archibald acts as a most interesting 

 interpreter to them as they examine the rocks exposed in 

 quarries, ravines, or sea-shores ; and there can be no 

 ctoubt that anyone who follows his instructions, and 

 observes according to his rules, will find himself in a fair 

 way to understanding the geological structure and historj- 

 of the particular district m which he is interested. It is 

 needless to say that the writing is clear and concise 

 throughout. We have only space to refer to the more 

 interesting parts of the book, and to those in which some 

 of the most recent results of geological science are intro- 

 duced. Beginners, who are usually rather hazj' in their 

 ideas of the difl'erent rocks composing the earth's surface, 

 should carefully study the excellent chapter on the deter- 

 mination of rocks, if they wish to be saved from endless 

 mistakes. The chapters on the tracing of boundary lines, 

 and the unravelling of geological structure, contain many 

 useful hints, the result of the author's wide experience in 

 geological surveying. One of the best chapters in the 

 book is that in which the igneous rocks, and their modes of 

 occurrence, are described. In the chapter on schistose 

 rocks and mhieral veins, we find references to some very 

 interesting recent discoveries about the sheering and 

 crushing of rocks. The schistose rocks have been sub- 

 jected to enormous pressure, and extensive deformation 

 has taken place; thus, in some conglomerates the pebbles 

 have been crushed and flattened, and even pulled out of 

 shape, whilst their sandy or gravelly matrix has been 

 converted into a schist. A crystallization of the crushed 

 material has taken place along the planes of sheering or 

 cleavage, thus causing foliation. Igneous rocks, too, have 

 sufi'ered in the same way. Dykes of basic rocks, such as 

 basalt, have been changed into fissile hornblende schists ! 

 In chapter X., the wonderful thrust-planes in the north- 

 west of Scotland are referred to. Sonic of the rocks 

 of that district have been pushed for many miles over 

 others. 



