Nov. 3, 1887] 



NA TURE 



19 



" Lightning" in Johnson's Encyclopaedia). Several hypothetical 

 cases are considered, and the author concludes that, ahhough his 

 computations may need some modification after further study, 

 we can safely say that no appreciable velocity of air is produced 

 by compression from falling rain. The same journal contains a 

 long paper on the theory of the wind-vane by Prof. G. E. 

 Curtis, reprinted from ihe American Journal of Science ior ]\\\y 

 last. He discusses the relative stability of a straight vane, and 

 that with a double or spread tail.. The first reference to the 

 latter is apparently in Voigt's Magazin^ 1797, and this form has 

 been in common use in England since about 1840. The formula; 

 show that for a frictionless bearing (i) that the oscillations of 

 both vanes are smaller as the vanes are longer and larger ; (2) 

 that the spread vane is always more stable than the straight 

 vane ; and (3) that this advantage in stability is greater for long 

 vanes than for short vanes, and is independent of the wind 

 velocity. The author finds that, with equal friction, a spread 

 vane is the more sensitive, and that consequently for two vanes 

 of equal sensitiveness the spread vane will have the greater 

 friction and will come to rest more quickly. 



Tazjahreslieric/tt of the Central Physical Observatory of St. 

 Petersburg for 1885 and 1886, and the Annalcn for the year 

 1885, have recently been published. The Russian system is 

 very important, not only as being the most extensive on the 

 globe, but on account of the great climatic contrasts and the 

 completeness of the observations. The present Director, Dr. H. 

 Wild, of Berne, was appointed in 1867, and iinder his able 

 superintendence the number of stations has greatly increased and 

 the quality of the observations has much improved. The central 

 Observatory is situated about a mile from the sea, on the island 

 of Wassili-Ostrow ; the principal observing department has been 

 transfen-ed since 1878 to Pawlowsk, about four miles distant, 

 and is placed under the superintendence of Dr. E. Leyst. The 

 observations for 1885 are contained in two quarto volumes of 

 about 700 pages altogether. In addition to the first class 

 observatories, the number of stations of the second order 

 amounts to 255, and of these the monthly and yearly results of 

 208 are published on the international scheme ; from 38 of the 

 stations the observations are published in extenso. Many new 

 stations have been added recently, especially in Siberia, and ia 

 newly-acquired territories, e.g. Merv, Batoum, &c. One of the 

 Siberian stations, viz. Werchojansk (iat. 67° 34', long. 133° 51') 

 is stated by Dr. Koppen to be the coldest known point of the 

 earth. The mean temperature there for the year was - 2^*9 F. 

 The mean for January and December was - 62° '9, and the 

 minimum in January - 88° '6 (far beyond the range of the usual 

 tables). The mean temperature of July rose to 60" '6, and the 

 minimum for that month was 39°'2. The number of rainfall 

 stations for which the observations are given is 650, against 252 

 in the previous year ; the data published are the monthly values, 

 the maximum fall in 24 hours, and the number of days of rain 

 and snow. A complete catalogue of the meteorological observa- 

 tions in Russia and Finland, by Dr. E. Leyst, giving the life- 

 history of each station, has been published in the Repertorium 

 Jiir Meteorologie this year. This work also contains many 

 valuable discussions of the vast amount of materials available 

 for the purpose. The index of the Annalen, being mostly in 

 Russian, is difficult to refer to. 



THE WORK OF THE INTERNATIONAL 

 CONGRESS OF GEOLOGISTS."^ 



I. 



T7 LEVEN years ago the Association met at Buffalo. It was 

 , the year of the Centennial Exhibition, and we were 



honoured by the presence of a number of European geologists. 

 This naturally opened the subject of the international relations 

 of geology, and the proposition to institute a Congress of Geo- 

 logists of the world took form in the appointment by the Asso- 

 ciation of an International Committee. The project thus initiated 

 found favour elsewhere, and there resulted an international 

 organization, which up to the present time has held three meet- 

 ings. It was convened first at Paris in 1878, then at Bologna in 

 1881, and at Berlin in 1885. Its next meeting will be held 



' Vice-Presidential Address read to Section E of the American Ass;ciation 

 for the Advancement of Science, August 10, 1887, by Mr. G. K. Gilbert. 



in London next year, and an endeavour will be made to 

 secure for the United States the honour of the fifth meeting. 

 The original Committee of the Association has been continued, 

 with some change of membership, and has sent representatives 

 to each session of the Congress. 



The work of the Congress, as originally conceived and as 

 subsequently undertaken, has for its scope geolc^ic nomenclature 

 and classification, and the conventions of geologic maps. The 

 particular classifications attempted are the establishment of the 

 major divisions used in historic and stratigraphic geology and 

 the subdivision of volcanic rocks. In nomenclature three things 

 are undertaken : (i) the determination of the names of historic 

 and stratigraphic divisions, (2) the formulation of rules for 

 nomenclature in palaeontology and mineralogy, and (3) the esta- 

 blishment and definition of the taxonomic terms of chronology 

 (period, epoch, &c. ) and of stratigraphy (system, series, &c.). 

 The map conventions most discussed are colours, but all signs 

 for the graphic indication of geologic data are considered. The 

 Congress has also undertaken the preparation of a large map of 

 Europe, to be printed in forty-nine sheets. 



The work was for the most part planned at the Paris meeting, 

 and Committees were appointed to formulate subjects for action 

 by the Congress at subsequent sessions. Briefly stated, the work 

 accomplished to the present time is as follows. Agreement has 

 been reached as to the rank and equivalence of the taxonomic 

 terms employed in chronology and stratigraphy, a set of rules for 

 palaeontologic nomenclature has been adopted, and many sheets 

 of the map of Europe have been prepared for the engraver. A 

 partial classification of stratified rocks has been agreed to, and 

 also a partial scheme of map colours, but the reports of pro- 

 ceedings indicate that action in these matters is tentative rather 

 than final. 



It is understood that b^th of these subjects will have promi- 

 nent place in the proceedings at the London meeting, and the 

 American Committee is endeavouring to prepare itself for repre- 

 sentative action at that meeting by ascertaining the opinions of 

 all American geologists on the various subjects. It has asked 

 this Section to set apart a day for the discussion of some of the 

 more important questions, and it can hardly be doubted that the 

 Section will realize the mutual advantage of thus assigning the 

 time requested. I am personally so impressed with the import- 

 ance of the possible work of the Congress that I shall devote 

 the present hour also to its consideration. 



The first thing the Congress did was to select names for a set 

 of categories to express the taxonomic rank of stratigraphic 

 divisions on the one hand, and of chronologic divisions on the 

 other. In the terminology of zoology and botany the words 

 kingdom, class, order, family, genus, species,- and so forth, 

 however difficult of definition they may severally be, neverthe- 

 less are used always in the same order of inclusion. No system- 

 atist in those sciences would think of grouping orders together 

 and calling them a family, or of- styling a group of families a 

 genus. But in geology there is no such uniformity of usage. 

 With some writers a group is larger than a series, with others it 

 is smaller. With some an age includes several periods, with 

 others a period includes several a^es. There are even writers 

 who ignore the distinction between stratigraphy and chronolc^; 

 and among the classifications submitted to the Congress is one 

 in which an age is subdivided in'o systems. There is a manifest 

 advanta'^e in bringing order out of this chaos, and si great is 

 the utility of uniformUy and perspicuity that the decisions of the 

 Congress in this regard will unquestionably be followed by- 

 future authors. The terms and the order adopted by the Con- 

 gress are as follows. Of stratigraphic divisions, that with the 

 highest rank is group, then system, series, and s'age. The corre- 

 sponding chronologic divisions are era, period, epoch, and_ age. 

 This order of rank is strange to most English readers and writers, 

 and so is one of the \.erm%— stage ; but the strangeness is only 

 a temporary disadvantage, and will not seriously retard the 

 adoption of the convention. The fact that we have previously 

 used the words in a different sense, or that their etymology 

 might warrant a different meaning, need not deter us, for we 

 know from frequent experience that the connotations of a word 

 transferred from one use to another quickly disappear from con- 

 sciousness, leaving it purely denotative. The introduction oJ 

 the word stage, which can hardly be said to have had an English 

 status heretofore, or at least the introduction of some new word 

 for that part of the column, was necessitated by the restriction 

 of the word formation to a special meaning— the designation ot 

 mineral masses with reference to their origin. 



