Feb. 



1887] 



NA TURE 



317 



most chemists employ it, they generally write it in an 

 elliptical form, shirking or ignoring the difficulties which 

 the fully-expanded formula too obviously suggests. But, 

 in spite of these drawbacks, we may say, without ex- 

 aggeration, that no formula ever exercised such an in- 

 lluence upon the progress of organic chemistry. Right 

 or wrong, final or only provisional, the benzene formula 

 grouped round it the scattered facts : each member of 

 the mysterious aromatic series found its proper place and 

 appeared in its proper light ; cases of isomerism were 

 predicted, even to their exact number ; and the synthesis 

 of important natural compounds, so high in the scale of 

 complexity as alizarin and indigo, was rendered possible. 

 The obs.ure corner is now a vast field, cultivated alike 

 by the scientific and by the practical chemist, and far 

 exceeding in extent the whole of the rest of organic 

 chemistry. 



The present work opens with an account of the benzene 

 theory. A very valuable feature in the mode of treatment 

 is the way in which the historical method is employed. 

 The much-enduring student of organic chemistry at the 

 present day is generally loaded with facts ; occasionally 

 the teacher condescends to furnish him with reasons ; but 

 not one student in fifty has any idea of the historical 

 genesis of the facts and reasons presented to him. The 

 ordinary text-books do little or nothing to supply this 

 want ; the exhaustive records of facts, like Beilstein's 

 " Handbuch,'" and the short text-books written for the 

 student can neither of them, although for different 

 reasons, spare the necessary space. Here the present 

 work comes to our aid. Nothing could well be more 

 instructive than the historical treatment of this very sub- 

 ject of the benzene theory as here given. The student is 

 enabled to see how the views at present held have been 

 evolved, step by step, from KekuWs formula. And in 

 this connection the earliest tentatives, however we may 

 despise them now, arc in their way as instructive as the 

 latest and most carefully- considered deductions. Witness, 

 for example, the historical tables which the authors give 

 in illustration of " orientation in the aromatic series " — 

 the determination of the position of the substituting 

 atoms or groups in the derivatives of benzene. The 

 reader can follow in detail the process by which errors of 

 method or of experiment were gradually eliminated, until, 

 ultimately, the present satisfactory condition of things 

 was reached, in which the same problem, attacked by 

 half a dozen independent methods, yields in every case 

 I the same result. The student who knows these things 

 I can give reasons for the faith that is in him, and he knows 

 that, no matter how the theory itself may change, the re- 

 lations worked out under the theory are permanent, and 

 that when the new theory comes, these relations will find 

 their places in it, differently expressed perhaps, but 

 unchanged in their interdependence. 

 L The descriptive portion of the work deals with benzene 



I and its derivatives, using the latter term in its narrow 

 sense, as excluding all derivatives which are homologous 

 or derived from homologues. There are certain disad- 

 vantages in this arrangement : thus, it separates widely 

 compounds which are closely related : toluene is not 



' Handbuch in German means, not a hand-book, but — luctts a non lucendo 

 — an exhaustive treatise which in most cases it would be physically impossible 

 to hold in the hand. 



treated of along with benzene, which it most closely re- 

 sembles ; the toluidines are separated from aniline, and 

 so on. Hut no system of classification is perfect ; and the 

 authors, as practical teachers, have doubtless satisfactory 

 reasons for adopting the foregoing arrangement. 



There is little further to be said about the descriptive 

 portion, the nature of which is sufficiently indicated by 

 the above account of its scope. The information is very 

 full. The interesting theoretical and historical discus- 

 sions are continued throughout the volume, and impart to 

 it a character of " readableness " rather unusual in a work 

 of this nature. Finally, the student of technology will 

 find the various manufacturing processes ti'eated of in 

 some detail. 



OUR BOOK SHELF 



Photography the Servant of Astronomy. By Edward 

 S. Holden. (Reprinted from the Onerland Monthly, 

 November 1886.) 



Half a century ago the attention of astronomers was 

 almost entirely confined to the study of the movements of 

 the heavenly bodies ; indeed, Bessel actually defined astro- 

 nomy as consisting therein. But since then an entirely new 

 department of astronomy has been developed, to which 

 the name "Astro-physics" has been given, and this new 

 department proceeds along three principal lines — spectro- 

 scopy, photometry, and photography. The great Obser- 

 vatory founded by the munificence of the late James Lic'c 

 is to be chiefly engaged in the development of the third 

 of these methods, though spectroscopy will also receive 

 a large share of attention. Having therefore in view the 

 chief purpose to which the great powers of his Observa- 

 tory will be devoted, the Director of the Lick Observa- 

 tory has here given a clear and concise account of the 

 principal services which photography has rendered to 

 astronomy in the past, and an analysis of those which 

 may be expected from it in the future. A description of 

 the facilities for photographic research possessed by the 

 Lick Observatory completes this interesting and instruc- 

 tive paper. Prof Holden mentions incidentally that Mr. 

 Grubb's ingenious device for placing the observer in 

 position for using the telescope, by raising or lowering the 

 entire floor, will be adopted in the great dome of the 

 Observatory. 



Observations nouvclles sur le Tu/eaie de Ciply et sur le 

 Cretaet! superieur du Hainaut. Par A. Rutot et E. 

 Van den Broeck. (Lidge : H. Vaillant-Carmanne, 

 1886.) 



In view of the stratigraphical gap that exists in this ooun- 

 try between the Chalk with Belemnitella inucronata and 

 the Thanet Sands, the papers thus re issued in a collected 

 form have an interest considerably beyond the district 

 with which they immediately deal. The value of passage- 

 beds being that they blur over the hard-and-fast lines laid 

 down by our earlier conceptions, it may seem ungrateful 

 to define the exact upward limit of deposits such as those 

 which close in the Danian series. The observations of 

 the authors, however, go to show that the Tufeau de Ciply 

 of the Mons basin, which has been hitherto referred to 

 the Maestrichtian — a fact incorporated in ordinary text- 

 book information — is in reality intimately connected with 

 the Montian. A close examination of 3000 kilogrammes 

 of the conglomerate that forms its base has yielded rolled 

 Tlieeidea and Cretaceous Bryozoa ; but the principal fauna, 

 as indicated by casts of unrolled shells, is of distinctly 

 Tertiary type, containing such representative forms as 

 Ccrithiiaii >nontense, Valuta elevata, and Turritella inon- 

 tcnsis. The beds near St. Symphorien, correlated with 



