October 24, 1884.] 



SCIENCE. 



397 



vey of the entire country, indicating the posi- 

 tion of points in the eastern portion of the 

 country which he thought most desirable to 

 occupy, in which the stations would be about 

 two hundred miles apart, regions of geological 

 disturbance avoided, but their sides occupied, 

 together with the summits of the higher moun- 

 tains. Seven or eight stations could be occu- 

 pied in a year, and thus a series of curves 

 secured which would give us the form of the 

 geoid ; i.e., of the surface beneath the conti- 

 nent where the force of gravhVy was uniform. 



In an interesting communication on the 

 theory of atomic volumes, Dr. Wolcott Gibbs 

 made the point that writers had left out of 

 consideration the volume of the interstitial 

 spaces. Mr. F airman Rogers described some 

 special features of Grant's difference-engine, 

 showing, that, by its method of calculating 

 tables by successive differences, it was an 

 improvement on previous arithmometers, elimi- 

 nating many sources of error. Those present 

 who had used such calculating machines be- 

 lieved them to be more useful in mathematical 

 than in astronomical work. 



Of papers other than physical, much in- 

 terest attached to the exhibition, by Mr. Pum- 

 pelly, of the first attempt to obtain a composite 

 photograph of the members of the academy. 

 Thirty-one photographs were obtained at the 

 last May meeting of the academy ; and three 

 composites had been made from the full-face 

 views, — one in which all were represented, 

 and two in which the ptrysicists and naturalists 

 had been separately combined. The latter 

 two showed marked differences, the physicists 

 having a much more oval face, and greater 

 temporal breadth. The common composite, 

 as well as the others, had a far more youthful 

 appearance than am T of the pictures from which 

 they were taken : only four or five at all ap- 

 proached them in this respect. Messrs. Peirce 

 and Jastrow's experiments on the question, 

 whether there is such a thing as a minimum 

 perceptible difference of sensation, or what 

 the Germans call differenzschwelle, w^ere in- 

 teresting. The experimenter arranged for the 

 production, by an assistant, of successive dif- 

 ferences of pressure upon the surface of his 

 own body, so slight that he was unable, so 

 far as he himself could judge, to either hear, 

 or see, or even feel them ; but actually, in 

 the majority of cases, determined correctly 

 whether the change was positive or negative. 



Of purely zoological papers there were few. 

 A paper by Professor Verrill gave an account 

 of the present season's work of the U. S. 

 fish-commission, which, b} r the steamer Al- 



batross, continues to bring from the deep sea 

 additional forms of animal life new to science. 

 and in great numbers. The most unexpected 

 result is the finding, in some of the deepest 

 dredgings, of large masses of exceedingly com- 

 pact cla}', instead of the usual globigerina and 

 other ooze. Dr. Packard showed, that, in a 

 blind isopod crustacean from the Mammoth 

 Cave, the brain differed from its allies only in 

 that traces of the pigment-la} T ers of the eye 

 remained more or less developed after the 

 entire abortion of the optic lobes and nerve. 

 Professor Cope believed he had found the 

 probable ancestors of the Mammalia in the 

 Pelycosauria, — an extinct type of reptiles, 

 which, of all reptilian types, shows at once 

 the most distinct batrachian and mammalian 

 features. 



Major Powell gave a succinct account of the 

 operations of the U. S. geological survey, ex- 

 hibiting two copies of the land-office map of 

 the country, — one colored to show the regions 

 which had been occupied ; the other, the broader 

 features of its geology. Mr. Pumpelly gave a 

 similar account of the work of the recently 

 closed Northern transcontinental survey, and a 

 special notice of the mesozoic coals met with in 

 that survey. By the study of transverse and 

 cross sections of the ciystalline tufa of Ne- 

 vada, Prof. E. S. Dana was able to determine 

 that the original form of thinolite was a steep 

 pyramid : it was probably a chloro-carbonate 

 of calcium, now altered to calcium carbonate. 

 Professor Brewer stated that in the dry regions 

 of the west, especially when several diy seasons 

 followed a succession of moister ones, in which 

 the lands were overstocked, the nutritious 

 grasses were eaten to death by cattle, and 

 thereupon supplanted by noxious types. Sev- 

 eral were mentioned as producing a rapid 

 obliteration of our native pastures, and their 

 seeds as injurious by piercing the skin, and 

 producing sores. 



Two reports called for by the government 

 had been transmitted to the president of the 

 academy, and will form a part of his annual 

 report to congress, — one upon the organiza- 

 tion of the scientific bureaus of the govern- 

 ment, called for by the commission, wmose 

 appointment we noticed in the first number of 

 this volume ; the other upon the proper clas- 

 sification of philosophical instruments under 

 the existing tariff regulations, called for by the 

 secretary of the treasury. A second quarto 

 volume of memoirs was announced as in the 

 hands of the binder. 



The next session of the academy will be its 

 annual meeting, next May, in Washington. 



