Feb. 5, [885] 



NA TURK 



329 



others have shown to be an essential part of the motion uf a 

 glacier cannot be produced by gravity alone. 



It was pointed out at the time that in Moseley's experiments 

 on the shearing strength of ice the element of time had been 

 disregarded, and a number of experiments have been since pub- 

 lished, chiefly on the bending of pieces of ice under the influence 

 of their own weight, which showed conclusively that the con- 

 tinuous action for a considerable time of comparatively small 

 forces will produce effects upon ice which the same forces are 

 quite incapable of producing in a short time. The nature and 

 conditio his of the motion were, however, very different from those 

 which we meet with in a glacier. 



Under these circumstances it seemed desirable that fresh 

 direct experiments on the shearing strength of ice should be 

 made under conditions differing as little as might be from those 

 under which ice actually shears in the interior of a glacier, and 

 it occurred to me that such experiments might be advantageously 

 made in one of the artificial grottoes which are now excavated 

 year after year for the benefit of tourists in several of the more 

 accessible Swiss glaciers. It seemed that it would be possible 

 in this way to carry out experiments upon glacier ice at a nearly 

 uniform temperature of about o' ('.. and under conditions as 

 nearly resembling those of the interior of a glacier as we can 

 hope to attain to in experiments on haul specimens of ice. 



I accordingly spent part of the long vacation of 1883 at 

 Grindelwald, and made a series of experiments in the grotto on 

 the right bank of the lower glacier, in order to see whether I 

 could obtain direct evidence of shearing under the influence of 

 forces comparable with those which Canon Moseley admits to 

 be capable of being produced by the action of gravity in a 

 glacier. 

 The experiments are fully described in the paper. Bai-sof ice 

 were passed through holes in three parallel blocks of wood, 

 nearly in contact with one another. The two outer blocks were 

 hung to a frame ^nd a weight was suspended from the middle 

 one. After the whole had hung for some days, the apparatus 

 was taken to pieces and the shear measured. In a final experi- 

 ment a shear of about '075 cm. was observed after the action for 

 about seventeen days of a shearing force of rather more than 

 200 grm. per square centimetre. 



The shearing force employed was indeed rather more than 

 double that which, according to Canon Moseley's calculations, is 

 exerted by gravity in the Mer de Glace, near the Tacul (Phil. 

 Mag. xxxvii. p. 369) ; but it is aboat r/25th of his [smallest 

 value of the shearing strength of ice, and the amount of shear is 

 larger than is implied in any of the ordinary cases of glacier 

 motion. 



I think then that there is little doubt that under conditions 

 closely resembling those of the interior of a glacier, and under 

 the influence of forces comparable with those which gravity is 

 capable of exerting in a glacier, hand specimens of ice shear in 

 the same manner as a truly viscous solid would do. 



Reasons are given for supposing that the range of temperature 

 through which ice is sensibly viscous is small ; the temperature 

 of the interior of a glacier is discussed, and it is pointed out 

 that the position of the " Bergschrund " so familiar in Alpine 

 literature corresponds to a point where there is a change in the 

 temperature of the lower part of the glacier, all below the 

 " Bergschrund " being :oft and viscous, all above it hard frozen 

 and immovable. 



The general result of the foregoing paper seems to be that the 

 fuller consideration of the physical properties of glacier ice leads 

 to essentially the same conclusions as those to which Forbes was 

 led forty years ago by the study of the larger phenomena of 

 glacier motion — that is, that the motion is that of a slightly 

 viscous mass partly sliding upon its bed, partly shearing upon 

 itself under the influence of gravity. To say this is, however, 

 byjio means to deny the importance of regelation in the 

 economy of a glacier. To regelation mainly we must attribute 

 the gradual passage of snow through the form of ntui into ice, 

 the healing of crevasses, and the possibility of comparatively 

 rapid and violent changes of form in portions of a glacier in 

 which unusually powerful forces may be supposed to be at work. 

 Moseley's argument, however, seems to be decisive against; the 

 belief that the ordinary comparatively undisturbed descent of a 

 glacier along a moderately sloping bed takes place by fracture 

 an 1 regelation. Moseley's value of the shearing strength of ice, 

 which has been shown to be enormously too great as a measure 

 of the re-istance of ice to slow shearing, would appear on 

 the other hand to be an inferior limit to the resistance to the 

 shearing fracture which must precede regelation. 



Royal Society, January 29. — " On the Structure and Rhythm 

 of the Heart in Fishes, "itli especial reference to the Heart of 

 the Eel." By J. A. McWilliam, M.D., Demonstrator of Physio- 

 logy in University College, London. (From the Physiological 

 Laboratory, University College.) Presented by E. A. Schafer, 

 F.R.S. 



The eel's heart presents some peculiarities in structure. The 

 auricle and ventricle are separated by a canalis auricularis. The 

 ventral wall of the sinus venosus does not end in the proper 

 auricular tissue but passes on to be attached directly to the ven- 

 tricle. The superficial part of the ventricular wall is supplied 

 by a special system of blood-vessels. 



When the ventricle is faradised, it is found that a slowly-inter- 

 rupted current (e.g. 3 per second) has a much more powerfully 

 stimulating effect than a rapidly-interrupted current (e.g. 50 per 

 second) of precisely the same strength. 



The inhibitory effects of stimulation of the vagus nerve-trunk 

 are very powerful ; the accelerating after-effects are slight and 

 variable. Vagus stimulation exerts no direct influence on the 

 ventricle ; it profoundly affects the auricle and sinus. It tem- 

 porarily abolishes the excitability of the auricular muscle and of 

 the muscular tissue entering into the composition of the ostial 

 part of the sinus. 



The manner in which the heart's action recommences after 

 vagal inhibition is peculiar ; the interjugular part of the sinus 

 and the ventricle beat before the auricle and the ostial part of 

 the sinus begin. 



The passage of a weak interrupted current through any part 

 of the auricle causes that part to stand still while the rest of the 

 auricle goes on beating. Curara obviates the occurrence of this 

 localised inhibition. 



Physical Society, January 24. — Prof. Guthrie, President, 

 in the chair. — Messrs. J. Rose Innes, A. Howard, and A. M. 

 Worthington were elected members of the Society. — Some lec- 

 ture experiments on spectrum analysis were shown by Mr. E. 

 Clemenshaw. The chief point in these experiments was the 

 production of a brilliant light without the use of the electric arc. 

 A small quantity of a solution of the salt to be experimented on 

 is put into a flask in which hydrogen is being evolved by the 

 action of zinc upon dilute sulphuric or hydrochloric acid ; the 

 bottle is provided with three necks, one being fitted with an 

 acid funnel, one with a jet, and by the other is introduced a 

 current of coal-gas, or better, of hydrogen, by which the size of 

 the flame can be increased and regulated. The jet, which is 

 about one-eighth of an inch diameter, is surrounded by a larger 

 tube, by which oxygen is admitted to the flame, the result being 

 a brilliant light giving the spectrum of the substance, which is 

 carried over mechanically by evolved hydrogen. The spectra of 

 sodium, lithium, and strontium were shown upon the screen, 

 and the absorption of the sodium light by a Bunsen flame con- 

 taining sodium was clearly seen. — An instrument to illustrate the 

 conditions of equilibrium of three forces acting at a point was 

 exhibited by Mr. Walter Baily. This instrument consists of a 

 circular disk of soft wood from the back of which an axle pro- 

 jects. The disk is provided with a graduated circle, and its 

 centre marked by the intersection of two fine lines upon a small 

 mirror. Three compound threads, each consisting of two 

 threads connected by a short piece of elastic, are knotted to- 

 gether, the free end of each being fastened to a pin. Two of 

 these pins are stuck into the disk at such a distance from the 

 centre that the knotted ends cannot reach the centre without 

 stretching each thread, and the remaining pin is then adjusted so 

 that this condition is fulfilled. There are now three forces in 

 equilibrium acting at the knot. The angles between their direc- 

 tions are obtained from the readings of the graduated circle 

 where it is crossed by the threads. To determine the magnitude 

 of these forces, the axle of the disk is held horizontally and 

 turned till a thread is vertical ; the pin is then removed, a scale- 

 pan attached to the end of the thread, and weights added till 

 the knot is brought back to the centre. This is repeated with 

 the other threads. It was found possible to show the propor- 

 tionality of the forces to the sines of the opposite angles with an 

 error not exceeding 1 per cent.— Mr. C. H. Hintonread a paper 

 on the " Poiograph." As the result of a process of metaphysical 

 reasoning, Mr. Hinton has come to the conclusion that relations 

 holding about "number" should be extended to space. Starting 

 from the premiss that the relation of a number to a number is a 

 number, e.g. the "relation" of 6 to 2 is 3, the author proceeds 

 to carry these principles into the consideration of space, and 

 concludes that, when properly understood, the relation of a 



