4IO 



NA TURt 



[February 28, 1895 



molecule, which can be accounted for quite simply in other 

 ways ; but it shows how prevalent is the idea that valency 

 means, not only the power to do something, but that 

 that power is always being exercised, and that in every 

 chemical formula every unit of valency must be accounted 

 for. This example is sufficient to illustrate the state of 

 confusion about valency and chemical combination, which 

 seems to grow more serious and more tangled every day. 

 The doctrine of Stereoisomerism as at present used 

 may be compared to the fluid theory of electricity. 

 It is a working theory which some day, perhaps, 

 will be superseded, but no great advance is likely 

 to be made until some more clear idea as to the 

 meaning of valency can be brought into use. In the 

 meantime experimental inquiry is undoubtedly proceed- 



near Eaux Chaudes. The impression, at a later date, 

 was deepened by the marvels of Adelsberg ; and a visit 

 to Han-sur-lcsse Belgium) in i8S8, determined him to 

 explore thoroughly the swallow-holes and caves of 

 Les Gausses -the limestone plateaux to the south and 

 west of the Cevennes and .\uvergne — with which he had 

 already made acquaintance. Here the rivers often tlow 

 through deep gorges — almost canons, such as is illus- 

 trated by Fig. I. In iSSS and the following year the 

 author investigated the underground topography of the 

 Departments of Lozore and Gard, and then extended his 

 researches from X'aucluse to La Charente, going as far as 

 the Puy-de-Dome, the Cote-d'Or, and Provence, and, 

 \et further afield, to Belgium, the Karst, and the 

 Peloponnesus. Altogether he explored 230 " holes in the 



Fir.. I. — Canon de la Daunie. 



ing rapidly, and will prepare the way for the next step in 

 theory. To this end such a book as Bischoff's " Stereo- 

 chemie" will afford much assistance in the laboratory, 

 and can be safely recommended to all who arc working 

 in this direction. W. A. T. 



CAVES AND SWALLOW-HOLES. 

 Ijs Abimes, les eaux sculeiraiiics. ks cavern, s, /, . 

 sources, la spelaologie. By E. A. Martel. 4 photo- 

 types and 16 plans, with 100 smaller illustrations. 

 (Paris: C. Delagrave, 1894.) 



A T the outset the author remarks that the man is 

 •^ happy who realises in ripe manhood a project of 

 boyhood. As a youth he was fascinated by the stalac- 

 tites of the cave of Gargas, and the underground stream 

 NO. 1322, VOL. 5 l] 



rock," which he thus classifies : Swallow-holes {(tbimcs 

 no, into 90 of which no descent had been previouslv 

 made ; emissaries of rivers [sources), 40, up 30 of which 

 no one had penetrated ; caves, 80, of which 45 wen 

 but imperfectly known. Besides these he had sounded 

 without descending, 35 swallow-holes, and examined 5 

 large emissaries, which could not be entered. Plans wen 

 made of underground galleries, the total length of whicl 

 amounts to 50 kilometres ; rather more than half tin 

 woik being done by himself, the rest by collaborators 

 The result of this indefatigable, and sometimes rathei 

 risky, work is the most complete original memoir on "cavi 

 hunting " that has ever been published, a quarto volunx 

 of nearly 600 pages, containing many plans, and still mon 

 numerous illustrations, the latter mostly from pliolo 

 graphs, together with a full bibliography of the subject. 



