250 



ELECTRICITY. 



their poles increases in the former cells, on stimuli 

 tion, and decreases in the latter. 



Variation in the Electrical Condition of the 

 Heart. It is known that during every revolu- 

 tion of the heart its muscular tissue undergoes 

 singular variations of temperature and excita- 

 bility, a diminution of excitability, and a rise 

 of temperature, coinciding with the systole, 

 while during diastole the opposite phenomena 

 are manifested. Supposing it to be probable 

 that corresponding variations of the electrical 

 condition of the cardiac muscle could be de- 

 tected, Marey has made a series of experi- 

 ments to determine this question. The gal- 

 vanometer, owing to the inertia of its needle, 

 is unsuitable for the observation of sudden 

 changes in the intensity of currents. Hence, 

 in Marey 's experiments, Lippmann's elec- 

 trometer was employed. The heart of a frog 

 was placed on two non-polarizable electrodes, 

 one of which supported the apex of the ven- 

 tricle, while the auricles rested on the other. 

 Two successive negative variations of the cur- 

 rent were indicated by the electrometer during 

 each cardiac systole : one of these was sudden, 

 and corresponded with the abrupt contraction 

 of the auricles; the other was more gradual, 

 and coincided with the slower movement of 

 the ventricle. The phases of electrical varia- 

 tion are thus seen to be similar to those of the 

 work done by the muscle. 



Influence of Light on the Electrical Be- 

 havior of Metals. In order to determine the 

 action of light upon the electrical behavior of 

 metals in water a subject which many years 

 ago engaged the attention of E. Becquerel 

 Hankel, a member of the Leipsic Gesellschaft 

 der Wissenschaften, employed two carefully- 

 cleaned and newly-scoured strips of copper, 

 one of which he fixed in a porous clay cell by 

 means of a cork stopper. This cell was filled 

 with water, and placed in a larger vessel of 

 glass containing some water, in which the 

 other copper strip was so immersed as to have 

 one of its surfaces turned toward the source 

 of light. The two strips having been con- 

 nected with the wire of a galvanometer, the 

 glass, with its contents, was placed in a black 

 case having a slide for the admission of direct 

 sunlight or colored light to the outer strip of 

 copper. The results were as follows : 



On access of free sunlight, the strip exposed to the 

 light was negative to the one in darkness, though 

 only moderately so; with red glass interposed, the 

 action was inconsiderable ; with yellow glass, a little 

 stronger; with green and dark-blue successively, 

 still stronger; with very dark-violet glass it was 



The copper strips were now oxidized by moderate 

 heating, and the following results were obtained : 

 In free sunlight the illuminated strip was strongly 

 negative ; on darkening again, the deflection grad- 

 ually disappeared ; behind red glass the action was 

 less ; behind light-yellow glass the plate was first 

 positive, then negative ; on darkening it became 

 still more negative, and then the action disappeared ; 

 behind dark-green glass the behavior wns similar, 

 but the first positive deflection was less; behind 



bright-blue, dark-blue, and violet glass, the plate 

 was equally negative. 



Strongly-oxidized copper strips were next tested. 

 In free sunlight the illuminated strip was first 

 strongly positive, then weakly negative, then the 

 action ceased. Behind red glass the plate was pretty 

 strongly positive, but the deflection of the needle 

 soon fell off considerably ; behind bright-yellow glass 

 the strip was very strongly positive, but very soon the 

 action diminished; on darkening, a strong negative 

 deflection occurred. Behind dark-green glass the 

 plate was first wenkly positive, and then negative ; 

 behind dark-blue glass it was also negative, and 

 this change was more considerable than with free 

 sunlight ; behind violet glass the action was similar. 



The author describes also the behavior of copper 

 in sulphate-of-copper solution, and the behavior of 

 silver, tin, brass, zinc, and platinum, which metals 

 were examined in the same way. 



Effects of Lightning on Different Species of 

 Trees. The effects of lightning on different 

 species of trees have been made a subject of 

 investigation by Daniel Colladon, who has 

 communicated to the Geneva Society of Nat- 

 ural History the results of his observations. 

 He states that when a poplar is struck all the 

 upper part of the tree remains perfectly sound 

 and green. The height above the ground at 

 which the injuries appear does not, in large 

 poplars, exceed one-third of the tree's height. 

 These injuries commence immediately below 

 the junction of the strong branches with the 

 trunk. In general, they do not reach quite to 

 the ground. It is always the tallest poplar of 

 a group that is struck. In some cases the 

 storm will pass over trees of other species and 

 will burst on poplars, though they be of less 

 height. The author has never met with any 

 traces of carbonization. The cases in which 

 several poplars are injured by a single dis- 

 charge of lightning are rare. One such case is 

 recorded by M. Colladon, where three poplars 

 were damaged by the same stroke. These trees 

 stood in a straight line, and about twelve feet 

 distant from each other. 



Magnetic Properties of Nickel and Cobalt. 

 The researches of Hankel into the magnetic 

 properties of nickel and cobalt are worthy of 

 being recorded here. The bars of these metals 

 used in his investigations were large and pure, 

 the nickel-bar being 168 millimetres long, 41.1 

 millimetres broad, and 13.1 millimetres thick; 

 the cobalt-bar was of nearly the same dimen- 

 sions. A bar of iron, of like dimensions, was 

 examined at the same time. Comparing the 

 iron with the nickel, it was found that, within 

 the limits of current-strength used, the mag- 

 netism in the former increased proportionally 

 to this strength ; the nickel at first, i. e., with 

 weak currents, showed nearly the same mag- 

 netic force as the iron ; very soon, however, 

 its magnetism increased in less degree than in 

 the iron, so that with the greatest strengths of 

 current it was little over a half of that in the 

 iron. The cobalt behaved like the nickel in 

 that, even with moderate currents, the mag- 

 netism increased in less degree than the inten- 

 sity of current ; but it differed in showing a 

 much less strength of magnetism within the 



