Jan. 3, 1884 



NA rURE 



227 



difference consists in the rel ■live size of the electrodes. For 

 example, in the case of a zinc-copper cell containing a siifgle 

 electrolytic fluid, the maximum cell is made with a kathode of 

 sheet copper folded and curved, presenting 300 times as much 

 surface as the thin copper rod which serves as anode, whilst in 

 the minimum cell the pr portion is reversed, so that the polarisa- 

 tion at the surface of the copper attains at once its maximum 

 value. The value of the E.M.F. of the cells when filled with 

 dilute sulphuric acid, and having the zinc amalgamated, was 

 I '072 vjlts maximum, and 0*272 volts minimum. Many other 

 electrolytes were examined by M. Keynier. The electromotive 

 force w.is measured upon a galvanomet'ir of high resistance. 



M. Reynier has suggested a modification of his maximum 

 cell to serve as a standard of electromotive force— namely, a cell 

 having a very large copper electrode, and a very small amalga- 

 n^ated zinc electrode, immersed in a solution of seasalt. Accord- 

 ing to M. Keynier, this battery ha; an E.M.F. of 0S2 volts, and 

 maintains this value within I per cent, even when the circuit was 

 loosed for tvio hours through a resistance of 820 ohms. M. 

 Reynier prefers this combination to one containing sulphate of 

 zinc in solution, because of the liability of the latter salt to 

 contain free acid. 



M. Henri Becquerel has been pursuing his researches upon 

 the infra-red rays of the spectrum. For the investigation of this 

 region there are four methods, the first of them involving the 

 use of a line-thermopile and a rock-salt prism ; the second, 

 Abney's photographic method ; the third, Langley's method, 

 with bolometer and a reflecting diffraction grating ; the fourth, 

 that of Becquerel, depending upon the discovery that the infra- 

 red rays have the effect of extinguishing the glow of a phosphor- 

 escent body exposed previously to ultra-violet rays. M. 

 Becquerel finds that water, for example, gives in the region to 

 which this method is applicable three well marked absorption- 

 band-, having wave-lengths respectively of 930, loSo, and 1230. 



The newest result of Becquerel's researches is worth more 

 than passing mention. He finds that there exist in this wholly 

 invisible region of the spectrum bright-line spectra — equally in- 

 visible, of course — just as in the visible parts of the spectrum, 

 ob ervable in the radiations of hot vapours. Thus, incandescent 

 soriium vapour prints upon the jjreviously " insolated " phosphor- 

 escent substance two well-marked lines (wave-lengths 819 and 

 109S), corresponding to two bright lines hitherto unknown. The 

 extent of the region which is capable of being explored by this 

 novel process is from wave-length 760 to 1300, or exceeding in 

 extent that of the whole of the visible and ultra violet rays. 



An interesting experiment is described in the Zeitschrift des 

 elektrotechnisclten Vereim, in Vienna, by Prof, von Waltenhofen, 

 made by means of Noe's thermo-electric generators. If a cunent 

 from a voltaic battery has been sent for a few moments through 

 one of these generators, it is capable of yielding a ciischarge like 

 a secondary battery. This effect is so far a mere repetition of a 

 well-known experiment of Peltier, and is due to the change of 

 temperature at the junction, called the Peltier effect. But von 

 Waltenhofen observes that the effects are different according to 

 the sense of the charging current. In one case, with increasing 

 chargii g currents the discharge currents also increased, and were 

 always in the opposite sense to that of the charging current. 

 But when the charging current was reversed, it was found that 

 with increasing charging currents the discharge currents at first 

 increase, then attain a maximum, then decrease to zero, then 

 actually recommence in the converse sense, namely, in the same 

 sense as that of the charging current. Prof, von Waltenhofen 

 is disposed to attribute this aramalous result to the lack of 

 symmetry in the di>position of the alternate soldering; of the 

 generators, and to their alternately unequal resistance causing 

 alternately unequal developments of heat due to resistance. 



In proof of the law of proportion between the thickness of a 

 square vibrating plate and its pitch, Dr. Elsas gives the follow- 

 ing neat experiment. Let three plates he cut from the same 

 sheet of material, of the same size and form. Cement two of 

 these together so as to produce a plate of double thicknefs 

 Then, on exciting the single plate and the double plate by 

 communicating to them respectively the vibrations of two tuning 

 forks whose pitches are as I : 2, the jjlates w ill be excited in 

 identical manners, as will be seen by dusting sand upon them, 

 the clang-figures being identical. 



Lord Rayleigh has reprinted for private circulation in 

 pamphlet form several of his most valuable optical papers, 



including those on the manufacture, reproduction by photo- 

 graphy, and theory, of diffraction-gratings, and those on colour- 

 mixtures. 



Lord Rayleigh has also reprinted some of his papers on 

 electricity and on absolute pitch, from Nature and from the 

 Reports of the British Association, in a convenient pamphlet 

 form. 



The question whether condensation of steam is a cause of 

 electrification has been examined afresh by S. Kalischer in the 

 Physical Laboratory at Berlin. According to the views of Fara- 

 day, this is a cau-e of electrification, and upon the alleged 

 phenomenon Prof. Spiing has founded a theory of the origin of 

 thunderstorms. Landerer thought he had heard sounds in the 

 telephone due to condensation of moisture on the linewirej. 

 Kalischer has in vain repeated the experiment. He has also 

 examined, by means of the quadrant electrometer, whether any 

 such electrification could be observed from the deposit of mois- 

 ture upon the surface of a vessel containing ice or some artificial 

 cooling mixture. The whole of the results were negative. 



Amongst the many recent suggestions for primary batteries is 

 one due to MM. Lalande and Chaperon, in which oxide of copper 

 is used as a depolarising agent. The oxide, in powder, is placed 

 in or on a sheet of copper or iron. The positive element is zinc, 

 and the exciting liquid caustic potash. A zincate of potash is 

 formed by the solution of the zinc. The cell is absolutely in- 

 active when the circuit is open. When closed, the current is 

 remarkably constant. According to Hospitaller, the electro- 

 motive force is O'gS volt. It must of course be closed from the 

 air, to prevent absorption of carbonic acid by the potash. The 

 reduced copper is reoxidised by simple exposure to the air. 



In a series of studies on the copper voltameter, published in 

 the Repcrtoriiiin der Physik by Dr. H. Hammerl, the following 

 conclusions are formulated : — i. The material condition of the 

 surface of the electrode, that is to say, whether it is covered 

 with a bright copper film or not, has no influence on the amount 

 of the depo-it. 2. The changes of concentration of the copper 

 solution, brought about in the voltameter by the current itself, 

 cannot be sufficiently prevented by stirring. 3. Heating the 

 fluid to boiling causes the deposit to come down almost com- 

 pletely in the state of cuprous oxide : it is partially oxidised 

 even at temperatures h' tween 40° and 60° C. 4. The greatest 

 permissible strength of current, for which the deposit may be 

 safely assumed to be a measure of the current, is about 7 amperes 

 per square decimetre of the cathode surface. 



THE EVIDENCE FOR EVOLUTION IN THE 



HISTOR V OF THE EXTINCT MAMMALIA ^ 

 T^HE subject to which I wi^h to call your attention this morn- 

 ing requires neither preface nor apology, as it is one with 

 the discussion of which you are perfectly familiar. My object 

 in bringing it before the general session of the Association was 

 in view of the fact that you were all familiar with it in a general 

 way, and that it probably interests the members of sections 

 which do not pursue the spec'al branch to which it refers, as 

 well as those w hich do ; also, since it has been brought before 

 us in various public addresses for many years during the meet- 

 ings of this Association, I thought it might be well to be intro- 

 duced at this meeting of this Association, in order that we 

 might not omit to have all the sides of this interesting question 

 presented. 



The interests which are involved in ii are large : they are chiefly, 

 however, of a mental and metaphysical character ; they do not 

 refer so much to industrial and practical interest-, nor do they 

 involve questions of applied science. They involve, however, 

 questions of opinion, questions of belief, questions which .Tffect 

 human happiness, I venture to say, even more than questions of 

 applied science ; certainly, which affect the happiness of the 

 higher grades of men and women more than food or clothing, 

 because they relate to the states of our mind, explaining as they 

 do the reasons of our relations to our fellow-beings and to all 

 things by which we are suiTounded, and the general system of 

 the forcts by which we are surrounded. So it has always ap- 

 peared to me : hence I have selected the department of biology, 

 and have taken a great interest in this aspect of it. 



I A lecture by Prof. E. D. Cope of Philadelphia, given in genera 

 session before the American Association for Advancement of Science at 

 Minneapolis, August 20, 1883. Stenographically reported for Science. 



