III. "On the Electromotive Changes connected with the Beat of the Mammalian Heart, and of the Human Heart in particular." By AUGUSTUS D. WALLER, M.D. Communicated by Professor BURDON SANDERSON, F.R.S. Received June 12, 1888.

(Abstract.)

1. Description of experiments in which the electrical variation connected with the spontaneous beat is modified.

2. The normal ventricular variation is diphasic, and usually indicates (1) negativity of apex, (2) negativity of base.

3. Description of "irregular" variations.

4. Observations on animals with one or both leading off electrodes applied to the body at a distance from the heart.

5. Determination of the electrical variations of the heart on man. 6. The variation is diphasic, and indicates (1) negativity of apex, (2) negativity of base.

7. Distribution of cardiac potential in man and animals. able" and "unfavourable" combinations.

"Favour

8. Demonstration of electrical effects by leading off from the sur. face of the intact body by the various extremities and natural orifices.

9. Comparison between effects observed on man with the normal and with a transposed situation of the viscera.

IV. "On the Plasticity of Glacier and other Ice." By JAMES C. MCCONNEL, M.A., Fellow of Clare College, Cambridge, and DUDLEY A. KIDD. Communicated by R. T. GLAZEBROOK, F.R.S. Received June 11, 1888.

The experiments described in the following paper were undertaken in continuation of those made by Dr. Main in the winter 1886-87, and described by him in a papert read before the Royal Society the following summer. The investigation is by no means complete, but the results hitherto obtained seem to us sufficiently novel and important to be worthy of being put on record, while we hope to

* Dr. Main used the term "viscosity." But this has been always applied in liquids to molecular friction, and we have the authority of Sir Wm. Thomson (Encycl. Britann.,' Art.: Elasticity, p. 7) for reserving it for the same property in solids also, leaving "plasticity" to denote continuous yielding under stress.

prosecute the subject further next winter. We shall first give a general account of our results, and then describe the experiments in more full detail.

Main found that a bar of ice, which had been formed in a mould,* yielded slowly but continuously to tension, though kept at a temperature some degrees below freezing point. We began work under the impression that the rate of extension depended mainly on the temperature and tension, and that the chief difficulty lay in keeping the temperature constant. But by a happy chance our very first experiment showed us that not merely the rate, but even the very existence of the extension depended on the structure of the ice. And this is a matter which seems to have been quite disregarded by previous experimenters.t

After many, and for the most part unsuccessful, attempts to obtain a piece of perfectly clear ice, frozen in the mould used by Main, we took a bar cut from the clear ice formed on the surface of a bath of water, and froze its ends on to blocks of ice fitting the two conical collars through which the tension is applied. To avoid any question as to the ice giving way in the collars, where it is subjected to pressure as well as tension-the bar was pierced near either end by a steel needle firmly frozen in, and the measurements were taken between the projecting ends of these needles. We found to our astonishment that the stretching was almost nil, though the tension was decidedly greater than that usually applied by Main. There was a slight extension at first, but during the last five days the extension observed was at the mean rate of only 0-00031 mm. per hour per length of 10 cm., and this may well be attributed to the rise of temperature which took place. The rigidity cannot have been due to the cold, for during the last 24 hours the temperature was between -1° and -2°. After the experiment, the ice was examined under the polariscope, and found to be a single regular crystal showing the coloured rings and black cross very well. The optic axis was at right angles to the length of the bar. This experiment showed it was a very necessary precaution to take the measurements between needles fixed in the bar itself. For whether the bar extended or not, the movement of the index H (fig. 2), showed

The mould produced a round bar of ice 24 cm. in length and 2.8 cm. in diameter, with a conical expansion at the lower end to fit into an iron collar C (fig. 2), through which the tension could be applied. The other end of the bar was frozen on to ice filling a similar collar B. These iron collars were faced with carefully worked brass plates, and Main determined the extension by measuring the distance between the plates with callipers.-July 6, 1888.

+ See Heim,' Handbuch der Gletscherkunde,' published by Engelhorn, Stuttgart, 1885, p. 315.

We use the centigrade scale of temperature throughout.

a decided separation of the collars due to the plasticity of the conical pieces of ice therein.

We next took a bar of ice formed in the mould, applied tension and took measurements in the same way. The extension was at the rate of 0.048 mm. pcr hour per length of 10 cm. The crystalline structure of this ice was highly irregular. As one principal object of our experiments lay in their application to the theory of glaciers, it had now become obviously most important to test actual glacier ice. We therefore drove over to the Morteratsch glacier, which is now readily accessible from St. Moritz even in the winter, and obtained some specimens from the natural ice caves at the foot of the glacier.

We tested three pieces, which were quite sufficient to disprove the common notions, that glacier ice is only plastic under pressure, not under tension, and that regelation is an essential part of the process. They showed at the same time the extraordinary variability of the phenomenon. The first extended at a rate of from 0.013 mm. to 0-022 mm. per hour per length of 10 cm., the variations in speed being attributable to temperature. The second piece began at a rate of 0.016 mm. and gradually slowed down till it reached at the same temperature a rate of 0.0029 mm., at which point it remained tolerably constant, except for temperature variations, till a greater tension was applied. The third piece on the contrary began at the rate of 0.012 mm., increased its speed with greater tension to 0·026 mm., and stretched faster and faster with unaltered tension, till it reached the extraordinary speed of 1.88 mm. per hour per length of 10 cm. We put on a check by reducing the tension slightly, whereupon the speed fell at once to 0:35 mm. and gradually declined to 0.043 mm. The lowest temperature reached during our experiments, except with the intractable bath ice, was with this specimen. During 12 hours with a maximum temperature -9° and a mean temperature probably -10.5°, the rate under the light tension of 1·45 kilo. per sq. cm. was 0.0065 mm.

These three pieces were composed of a number of crystals varying in thickness from two or three millimetres up to thirty or even a hundred. These crystals are the "glacier grains" (gletscherkörner), which play such a large part in glacier literature. Glacier ice is a sort of conglomerate of these grains, differing, however, from a conglomerate proper in that there is no matrix, the grains fitting each other perfectly. In the winter, at any rate, the ice on the sides of the glacier caves looks quite homogeneous. But, when a piece is broken off and exposed to the sun's rays, the different grains become visible to the naked eye, being separated probably by thin films of water. Though the optical structure of each grain is found under the polariscope to be perfectly uniform, the bounding surfaces are utterly irregular, and are generally curved. The optic axes too of

neighbouring grains seem to be arranged quite at random. Owing to the structure being so complex, we failed to trace any relation between the arrangement of the crystals and the rapidity of extension. It is true that the most rigid piece of the three was composed of small crystals, while the most plastic contained one very large crystal; but this was perhaps accidental. Fortunately, we were able to obtain ice of a more regular structure, which has already thrown a little light on the action at the interfaces of the crystals, and offers an attractive field to further investigation.

Some of the ice of the St. Moritz lake is built up of vertical columns,* from a centimetre downwards in diameter, and in length equal to the thickness of the clear ice, i.e., a foot or more. A horizontal section, exposed to the sun for a few minutes, shows the irregular mosaic pattern of the divisions between the columns. The thickness of each column is not perfectly uniform. Sometimes indeed one thins out to a sharp point at the lower end. Each column is a single crystal, and the optic axes are generally nearly horizontal. Some experiments on freezing water in a bath, lead us to attribute this curious structure to the first layer of ice having been formed rapidly, in air, for instance, below -6° C. We found that if the first layer had been formed slowly, and was therefore homogeneous with the axis vertical, a very cold night would only increase the thickness of the ice, while maintaining its regularity.

We applied tension to a bar of lake ice carefully cut parallel to the columns. It stretched indeed, but excessively slowly. During seven days it stretched at the rate of only 0.0004 mm. per hour per length of 10 cm., though at one time the temperature of the surrounding air went up above zero. The tension was 2 kilos. per sq. cm. This slight extension may well be attributed to the tension not being exactly parallel to the interfaces of the columns. This experiment corroborates our first result, that a single crystal will not stretch at right angles to its optic axis. We next cut a bar at about 45° to the length of the columns, and the difference was very manifest. During 80 hours under a tension of 2.75 kilos. per sq. cm., it extended at the rate of 0.015 mm. per hour per length of 10 cm., nearly 40 times as fast.

An icicle is an example of ice formed of very minute crystals irregularly arranged. We found that an icicle under a tension of 2.2 kilos. per sq. cm. stretched at the rate of 0·003 mm. per hour per length of 10 cm. This is very slow, especially as the temperature

This was the case in all pieces obtained from one end of the lake, where men were cutting ice for storage purposes, whether new ice or old. In a part, however, which had frozen a few days earlier, further out from the shore, we found much larger crystals with the axes nearly vertical but not quite parallel to each other.— July 6, 1888.

was high, averaging -1° C., yet it is difficult to suggest any theoretical reason for an increase in the number of interfaces producing a decrease in the plasticity.

We tried further two experiments on compression of ice, the pressure being applied to three nearly cubical pieces at once. Of three pieces of glacier ice, under a pressure of 3-2 kilos. per sq. cm., the mean rates of contraction during five days were respectively 0.035 mm., 0.056 mm., and 0·007 mm. per hour per length of 10 cm. These figures show that while the plasticity varies enormously in different specimens, the rate of distortion is of the same order of magnitude, whether the force applied be a pull or a thrust.

The other experiment was on three pieces of lake ice, applying the pressure in a direction parallel to the columns. The contraction was scarcely perceptible. Under a pressure of 37 kilos. per sq. cm., the mean rate of the three pieces during four days was 0.001 mm. per hour per length of 10 cm. To fix the blocks of ice in position, we found it necessary to cover their ends with paper frozen on, and the small contraction observed may well be attributed to the yielding of the films of irregular ice with which the paper was attached. This view is supported by the fact that nearly the whole of the contraction took place in the first 36 hours.

We have now shown by direct experiment that ordinary ice, consisting of an irregular aggregation of crystals, exhibits plasticity, both under pressure and under tension, at temperatures far below the freezing point—in the case of tension at any rate down to -9° at least, and probably much lower-and also that a single uniform crystal will not yield continuously either to pressure or tension when applied in a direction at right angles to the optic axis. We fully intended to test a crystal under tension applied along the optic axis; but we were unsuccessful in obtaining a crystal longer in the axis than perhaps 8 cm., and when we had decided to be content, with that length, a thaw put a stop to all further operations. We have, however, very little doubt that a crystal would refuse to yield either to pressure or to tension in whatever direction they were applied.

The following reasoning seems tolerably conclusive as far as it goes. We first assume the axiom that, if two systems of stresses produce each by itself no continuous yielding, superposition of the two will likewise produce no continuous yielding. This will probably be admitted when we add the proviso that, when the nature of the resultant stresses is found, their magnitude is to be reduced to the same value as that of the simple stresses which are known to be inactive. Take then a cube of ice, two of whose faces are perpendicular to the optic axis. Apply tension to one of the other pairs of faces. This according to our experiments produces no extension.