December i, 1892 J 



NATURE 



n7 



done nothing more than follow such authorities as Lord Kelvin, 

 Dr. Lodge, and Mr. O. Heaviside in the matter. — The discus- 

 sion on Mr. Sutherland's paper, on the laws of molecular force, 

 was reopened by Prof. Perry reading a communication from 

 the President, Prof. Fitzgerald, lie objected to discontinuous 

 theories, especially when Clausius had given a continuous 

 formulae much more accurate over a very long range than Mr. 

 Sutherland's discontinuous ones. The introduction of Brownian 

 motions without carefully estimating the rates required and 

 energy represented, and without giving any dynamical explana- 

 tion of their existence, was not satisfactory. It would, he said, 

 be most interesting if Mr. Sutherland would calculate the law 

 of variation of temperature with height of a column of convec- 

 tionless gas, under conduction alone (for Maxwell thought the 

 inverse fifth power law of molecular attraction was the only one 

 that gave uniformity of temperature under these conditions), 

 and if necessary make tests with solid bars. Referring to the 

 statement that molecular attraction at one cm. was comparable 

 with gravitation at the same distance, he thought Mr. Boys 

 would question this, and he suggested an experimentiim cruets 

 of the inverse fourth power law. Both the inverse fourth and 

 inverse fifth power laws, assumed symmetry which did not exist. 

 He also took exception to other parts of the paper. Dr. Glad- 

 stone, referring to the relative dynic and refraction equivalents 

 given in Table XXVIIL of thepaper,said he thought it interesting 

 to make a similar comparison between dynic and dispersion and 

 magnetic rotation equivalents. The result as exhibited in a 

 complete table showed a certain proportionality between the 

 four columns but the differences were beyond the limits of 

 experimental error. Mr. Sutherland, however, sometimes 

 reckoned the dynic equivalent of hydrogen as o'2i5, and at 

 other times looked upon it as negligible. The analogies be- 

 tween the optical equivalents did not depend on the propor- 

 tionality of the numbers so much as upon the fact that the 

 refraction, dispersion, and magnetic rotation equivalents of a 

 compound was the sum of the corresponding equivalents of its 

 constituent atoms, modified to some extent by the way in which 

 they were combined. Whilst a somewhat similar relation held 

 true for the dynic equivalents, the effect of "double-linking" 

 of carbon atoms, so evident in the optical properties, was 

 scarcely perceptible. The result of calculating the constants 

 from M/ instead of from M-/ was next discussed, the effect of 

 which was to quite upset the proportionality before noticeable. 

 Mr. S. H, Burbury said that on referring to the author's 

 original paper, on which the present one was based, he found 

 that a uniform distribution of molecules was assumed. On this 

 supposition the demonstrations given were quite correct, and 

 the potential was a maximum. If, however, the molecules 

 were in motion the average potential must be less than the 

 maximum, and the deductions in the present paper being based 

 on wrong assumptions were liable to error. Prof Ramsay 

 remarked that many statements in the paper, on the subject of 

 critical points, were very doubtful. Separate equations for the 

 different states of matter were not satisfactory, neither was the 

 artificial division of substance into five classes. The predicted 

 differences in the critical points due to capillarity, had not been 

 found to exist. Speaking of the virial equation, he said that 

 hitherto R had been taken as constant. Considerations he had 

 recently made led him to believe that R was not constant. The 

 whole question should be reconsidered regarding R as a variable. 

 Mr. Macfarlane Gray said he had been working at subjects 

 similar to those dealt with in Mr. Sutherland's paper, but from 

 an opposite point of view, no attraction being supposed to 

 exist between molecules. In the theoretical treatment of steam 

 he found that no arbitrary constants were required, for all could 

 be determined thermo-dynamically. The calculated results 

 were in perfect accord with M. Cailletet's exhaustive experi- 

 ments except at very high pressures, and even here, the theo- 

 retical volume was the mean between those obtained experi- 

 mentally by Cailletet and Battelli respectively. Prof. Herschel 

 pointed out that Villar9eau had discussed the equation of the 

 virial, where the chemical and mechanical energies were not 

 supposed to balance each other. Mr. Sutherland's paper all 

 turns on the existence of such a balance, and he (Prof. Herschel) 

 could not understand why this balancing was necessary. The 

 discussion was then closed, and the meeting adjourned. 



Geological Society, November 9. — W. H. Hudleston, 

 F.R.S., President, in the chair. — The following communications 

 were read : — A sketch of the geology of the iron, gold, and 

 copper districts of Michigan, by Prof. M. E. Wadsworth. 



NO. 1205, VOL. 47] 



After an enumeration of the divisions of the azoic and palaiozoic 

 systems of the upper and lower peninsulas of Michigan, the 

 author describes the mechanically and chemically formed azoic 

 rocks, and those produced by igneous agency, adding a table 

 which shows his scheme of classification of rocks, and explain- 

 ing it. The divisions of the azoic system are then described in 

 order, beginning with the oldest — the cascade formation, which 

 consists of gneissose granites or gneisses, basic eruptives and 

 schists, jaspilites and associated iron ores, and granites. The 

 rock of the succeeding republic formation are given as nearly 

 as possible in the order of their ages, commencing with the 

 oldest : — Conglomerate, breccia and conglomeratic schist, 

 quartzite, dolomite, jaspilite and associated iron ores, argillite 

 and schist, granite and felsite, diabase, diorite and porodite, and 

 porphyrite. The author gives a full account of the character, 

 composition, nnd mode of occurrence of jaspilite, and discusses 

 the origin of this rock and its associated ores, which he at one 

 time considered eruptive ; but new evidence discovered by the 

 State Survey and the United States Survey leads him to believe 

 that he will have to abandon that view entirely. In the newest 

 azoic formation, the Holyoke formation, the following rocks are 

 met with: — Conglomerate, breccia and conglomeratic schist, 

 quartzite, dolomite, argillite, greywacke and schist, granite and 

 felsite (?), diabase, diorite, porodite, peridotite, serpentine, and 

 melaphyre or picrite. The conglomerates of the Holyoke 

 formation contain numerous pebbles of the jaspilites of the 

 underlying republic formation ; a description of the Holyoke 

 rocks is given, and special points in connexion with them are 

 discussed. The author next treats of the chemical deposits of 

 the azoic system, gives a provisional scheme of classification of 

 ores, and discusses the origin of ore deposits. The rocks of 

 the palaeozoic system are next described, and it is maintained 

 that the eastern sandstone of lower silurian age underlies the 

 copper-bearing or Keweenawan rocks. The veins and copper 

 deposits are described in detail, and the paper concludes with 

 some miscellaneous analyses and descriptions, as well as a list 

 of minerals found in Michigan. After the reading of this paper, 

 the President noted that it presented three sets of questions of 

 much importance, viz. , those bearing on the archsean rocks, the 

 iron deposits and jaspilites, and the copper and gold deposits re- 

 spectively. As regards the classification of the archaean rocks, 

 some might wonder what the terms used by the author meant. 

 The words laurentian and huronian used in Canada seemed not 

 to be tolerated in Michigan. The officers of the United States 

 Geological Survey have described all the archaean formations 

 noticed by the author ; the cascade as the fundamental complex, 

 the republic as the lower marquette, and the Holyoke as the 

 upper marquette. Was each State of the Union going to divide 

 these archaean rocks after its own fashion ? With regard to the 

 iron rocks, he would observe that the author, after enumerating 

 all the views in favour of their volcanic origin, now admitted 

 that he was wrong, and that Irving and others were correct. 

 The most important question was how the iron ores were really 

 formed, and to this it was difficult to find a complete answer in 

 the paper. Sir Archibald Geikie remarked that it was hardly 

 possible to criticize a voluminous paper of this nature, in the 

 reading of which much of the detailed statement of facts was 

 necessarily omitted. One of its most interesting points related 

 to the nature and classification of the rocks intermediate between 

 the base of the Cambrian system and the oldest or fundamental 

 gneisses. The plan which Prof. Wadsworth followed of adopt- 

 ing local names for the several subdivisions of the series in each 

 region was no doubt in the meantime of advantage, until some 

 method of correlation and identification from region to region 

 could be discovered. But it unavoidably led to temporary con- 

 fusion, for the same rock-group might turn out to have received 

 many different names. He thought it would be of service if 

 geologists could agree upon some general term which would 

 denote the whole of the sedimentary groups or systems which 

 intervene between the old gneisses and the Olenellus-zone. 

 Various names had been proposed, such as azoic, eozoic, pro- 

 terozoic, algonkian, to each of which some objection may be 

 raised. The existence of a number of very thick systems of 

 sedimentary deposits between the base of the Cambrian forma- 

 tion and the gneisses was now well established in this country 

 and in North America. In the upper members of this series 

 fossils had been found, and it might eventually be possible to 

 group the rocks by means of pal aeon tological evidence. But in 

 the meantime it would be convenient to class them under one 

 general name which would clearly mark them off from the true 

 archaean gneisses, &c., below them and the palaeozoic rocks 



