October i8, 1906] 



NA TURE 



607 



suitable for viTy low voltages in the armatures. For 

 instance, the input of the 60 h.p. motor is about 620 

 amperes at 100 volts. This choice of voltage no doubt 

 greatly facilitates the design from the point of view 

 of a low transformer voltage, but such a choice would 

 be almost impossible for traction work, owing to size 

 of the controlling gear. At this voltage the current 

 required by four 100 h.p. motors in parallel would be 

 approximately 4000 amperes; and ev-en, if connected 

 two series two parallel, the control of 2000 amperes 

 would involve very heavy cables and switches. 



If, on the other hand, a higher voltage had been 

 chosen, a higher value of the transformer voltage 

 would have resulted ; but this is precisely the difficulty 

 which has to be met in practice. For railway work, 

 voltages less than 220 are practically unknown. 



The book concludes with two appendices, the first 

 of which deals with the theory of the repulsion motor, 

 taking account of magnetic saturation, and the shift- 

 ing of the brushes ; and the second gives some oscillo- 

 graph tests dealing with the commutation of a small 

 motor operating with alternating currents. 



Mr. R. F. Looser, in translating this book from the 

 German, has accomplished his task with excellent 

 results. 



I0LC.4.V/C HISTORY OF AVVERGNE. 

 L'.lt.'t' des dentiers Volcaiis de la France. By 

 Marcellin Boulr. La Geographie (Mars, Mai, 

 1906.) Pp. 64; illustrated. (Paris: Masson et Cie.) 



THE volcanic outbursts of Auvergne are to a certain 

 extent disconnected locally and different in age. 

 The western group is the more linear in arrangement, 

 the eastern the more sporadic. In the one, the broad 

 mass of the Cantal sends off a short spur — Aubrac — 

 to the south-east, and a long one to the north, which 

 extends through the famous Mont Dore district and 

 terminates in the chain of Puys west of Clermont- 

 Ferrand ; in the other group we have the noted chain 

 of the Velay and the outlier of Mezenc, Megal, and 

 Coirons. The eruptions, apparently, were the latest to 

 begin in the first of these districts, and the latest to 

 cease in the region of the northern Puys. The tuffs 

 and other sedimentary deposits, which are associated 

 with the lava flows and masses of coarser scoria, have 

 furnished palaeontological data which fix the age of 

 some of the volcanic outbursts, and make it possible 

 bv a comparative study of the ejecta to synchronise 

 the discharges in different districts. The materials 

 oscillate from basalts to andesites, with fairly 

 abundant phonolites in two areas, and occasional 

 rhyolites and trachytes among some of the older 

 rocks. The earliest outbursts occurred in the Upper 

 Miocene. Volcanic activity ceased in one of the 

 southern extremities with the Lower Pliocene, in 

 another with the Middle, in the Cantal itself with the 

 Upper. It was prolonged in four districts well into 

 the Quaternary, the date of its cessation being still 

 far from certain. 



In the neighbourhood of Le Puy, eruptions, as the 

 discovery at Denise showed in 1844, were contempor- 

 aneous with Palsolithic man. The evidence of the 

 NO 1929, VOL. 74] 



Gravenoire skeleton (found in 189 1) is doubtful, as it 

 is from one or two other places, while that from 

 Pranal, Blanzat, St. Saturnin, and Neschers is nega- 

 tive. There is none anywhere to show that eruptions 

 were contemporary with Neolithic man ; but an 

 awakening, as Vesuvius once proved, is possible after 

 ;i long slumber. Has this been the case in Auvergne? 

 For that, according to some authorities, we have 

 historical evidence. Here Prof. Boule's title and pre- 

 face led us to hope for some additional information, 

 but we have been disappointed. In fact, his dis- 

 cussion of the evidence is hardly so full as that which 

 it received in the Geological Magazine so long ago 

 as 1S65. .^s was then stated, several earthquakes 

 occurred about the year 451 a.d., and the wild deer 

 became so terrified as to take refuge in Vienne. A 

 third " portent " happened, but whether this was a 

 volcanic eruption depends on the translation of certain 

 Latin words in two letters written by bishops. If 

 these refer to severe fires — possibly the consequences 

 of the earthquakes — the language is e.xtraordinarily 

 bombastic; if to an isolated volcanic outbreak, this 

 could not be in the " Puy " district, and there is much 

 difficulty in locating it nearer Vienne. We do not 

 find that the uncertainty has been diminished bv Prof. 

 Boule's researches; but, notwithstanding this dis- 

 appointment, and though most of the information has 

 been already published, we welcome as a boon to 

 students this clearly written summary of the volcanic 

 history of .Auvergne from one who has taken such a 

 leading part in its elucidation. T. G. Bonnev. 



OUR BOOK SHELF. 

 The Birds of the British Islands. In twenty parts. 



By Charles Stonham, C.M.G. With illustrations 



by L. M. Medland. Part i. Pp. 40 and plates. 



(London : E. Grant Richards, 1906.) Price ys. 6d. 



net. 

 To use the language of sport, Mr. Stonham may 

 claim to have established a new record. He has 

 aimed at a colourless book, and colourless it is, both 

 in the plates and in the text, though whether it is 

 " far in advance of anything of the kind which has 

 so far been attempted " must be left to the individual 

 judgment of the reader. 



In saying this, however, we are far from imply- 

 ing, or wishing to imply, that the work is without 

 merit; it gives a careful and pleasing description of 

 the species and their habits, and shows considerable 

 acquaintance on the author's part with most of them; 

 but nothing strikes us as impressive, nothing as an 

 addition to our knowledge, nothing, in short, as 

 unlike what may be found without much trouble else- 

 where. 



."Ml this may, of course, be altered when families 

 other than the Turdida come under discussion, but in 

 this part — and it is this part that we are called upon 

 to notice — we can see no sufficient reason for the 

 publication of the work. Nevertheless, we infinitely 

 prefer it to many other books treating of British 

 birds, and hope, for the author's sake, that it may 

 meet with more success than we anticipate. We can 

 hardly believe, however, that the considerations of fine 

 paper, brilliant ink, and so forth, advanced in the 

 prospectus, will outweigh those of comparative cost. 

 61. 15^. is no small price for a publication of this 

 kind with black plates, especiallv when it is proposed 



