November 9, 1893] 



NA TURE 



41 



attached to them as an agent of erosion. They must act like 

 so many gigantic drills upon the rock surface, and dig out 

 hollows similar to those found at the foot of an ordinary water- 

 fall. It may be objected that, when the glacier has retreated, 

 we ought to find, instead of one large hollow, a series of pits 

 corresponding to the position of each moulin ; but here the 

 peculiar conditions afforded by the presence of the ice come 

 into play. Any particular moulin never keeps the same posi- 

 tion for any length of time, not only because a new crevasse 

 may open at any point in the course of the stream, but also 

 because the water is continually cutting back the edge of the 

 fall, as in an ordinary waterfall, but much more quickly. Thus 

 the drills, in course of time, work backwards and forwards over 

 the whole of the area occupied by this portion of the glacier. 

 Indeed, their action may be compared to that of a rapidly 

 revolving drill moved slowly over the surface of a piece of 

 wood, which would ultimately be cut out to any desired depth, 

 •or to the action of a sand-blast directed on a piece of plate-glass. 



It may be noted that none of the streams find their way dov/n 

 the glacier as far as the mass of moraine matter near its lower 

 end, so that they can have no effect on the rock barrier, which, 

 as I have pointed out, has a tendency to form beneath that por- 

 tion of the glacier. Moreover, the majority are swallowed up 

 before they reach the lower third or so of this middle portion 

 ■of the glacier, and thus the well-known section of the bed of 

 those rock basins which have been attributed to glacial action, 

 •deepest near their upper ends, and gradually shallowing lower 

 down, is simply and easily accounted for. 



It is a curious fact that, in the Himalayas, true rock basins are 

 of very rare occurrence, although the conditions for their for- 

 mation on the above hypothesis are conspicuously present. It 

 is not, however, difficult to account for their absence if we con- 

 sider the enormous amount of debris carried down by the Hima- 

 layan glaciers as compared with that borne by most European 

 glaciers, to judge from pictures and photographs of the latter, 

 it is only the lower portion of the Himalayan glaciers that is so 

 entirely covered by debris, and the difference may be partly 

 due to the fact that the hill-sides above this portion of the glacier 

 are much less protected by ice and snow than in the case of the 

 northern glaciers. On the retreat of the glacier this burden of 

 moraine stuff would be quite sufficient to fill up any hollow 

 ■that may have been formed beneath it. This is well shown in 

 the accompanying illustration, where there is a well-defined old 

 moraine at a, the present termination of the glacier being at b. 

 Between these two points stretches an almost level plain, some 

 four or five miles long, in which we should have expected to 

 find a lake, supposing a hollow had been worked out beneath 

 the glacier ; but in place of it we find this broad stony plain 

 -covered with debris, evidently derived from the main glacier 

 and from the side valleys. But suppose the glacier were to 

 advance again, all this loose material would in course of time 

 become frozen into the bottom of it, and carried out. Then if a 

 rapid retreat of the glacier were to occur, leaving no time for 

 the hollow — if any exists — to be filled up again, we might have 

 a lake where the plain now is. Or, the contrast may perhaps 

 be accounted for by a difference in the rate of change of climate 

 since the glacial period, which may have been more slow in 

 these southern latitudes than further north, so that the northern 

 glaciers had not sufficient time during their retreat to fill up 

 the hollows formed beneath them. If, as has been supposed, 

 the extension of the European glaciers was partly due to a 

 diversion of the Gulf Stream, might not the rapid breaking down 

 of the barrier which caused that diversion have given rise to 

 the rapid amelioration of climate required? 



It would not, I think, be difficult to carry out a few measure- 

 ments of the erosion that goes on beneath a glacier, which 

 might throw much light on the question. If one visits the 

 mouth of one of these glaciers early in the morning, the stream 

 which issues from it is seen to be nearly, but never quite, free 

 from sediment. This amount of sediment might, I think, be 

 taken as that due to the rasping action of the ice itself, aided 

 by the rocks frozen into its under surface. As the day proceeds, 

 and the surface of the glacier begins to melt, the volume of 

 water issuing at its foot quickly increases, and at the same time 

 it becomes thick with mud. It would be easy to measure the 

 velocity of the stream, and the amount of sediment at intervals 

 during the day, and from this, knowing the area of the glacier, 

 we could estimate the erosion due respectively to the rasping 

 action of the ice and to the drilling action of the moulins. That 

 the latter would be enormously in excess of the former I have 



NO. 1254, VOL. 49] 



no doubt whatever, and I think that it is worth considering 

 whether this may not be an adequate cause of those hollows 

 which do undoubtedly occur in positions that seem to connect 

 them with a former extension of glaciers. 



T. D. LaTouche, 



CHRONO-PHO TOGRAPHIC S TUB V OF THE 



LOCOMOTION OF ANIMALS} 

 'X'HE chief interest in the study of organised beings is to look 

 ■*■ for the similarity which exists between the special con- 

 formation of each species, and the particular characters of the 

 functions in this species. 



The union of comparative anatomy and physiology is becom- 

 ing more and more close, and will, without doubt, lead to the 

 discovery of the fundamental laws of morphology — laws by 

 means of which the inspection of an organ will permit us to 

 foresee the particularity of its function. 



These relations begin to be comprehensible in the case of the 

 organs of locomotion of vertebrates. The size and length of the 

 muscles, the relative dimensions and forai of the bony supports of 

 the members, the extent and the form of the articulating sur- 

 faces enable us to infer the character of the movements of mam- 

 mals ; and, on the other hand, the accuracy of these deductions 

 can be proved by controlling them by chrono-photography, 

 which gives the geometrical character of these movements. 



Attempts have been made to extend this method of analysing 

 the moveoients of a number of difi'erent animal species by 

 chrono-photography, and they have been successful not only 

 with mammals, but also with birds, . reptiles, fishes, molluscs, 

 and arthropods. 



It will no doubt be a lengthy enterprise to collect the 

 numerous series of pictures necessary for this comparison, but 

 we have been able to assure ourselves that it is nearly always 

 possible to obtain such pictures by varying the conditions 

 according to the kind of animal studied. 



Reptiles, for example, must be put in a kind of circular 

 canal, where they can run at their ease ; the chrono-photo- 

 graphic apparatus is placed above the path in which the 

 animal runs, and thus photographs the successive attitudes 

 during the course. 



The fish swim in similar troughs filled with clear water, and 

 illuminated underneath, in order that their silhouettes should 

 appear on a clear background. At other times the animal is 

 lighted from above, and thus appears light on a dark back- 

 ground. Similar arrangements are employed for insects. _ It 

 is not necessary to have here the dark background which 

 served for the study of mammals and birds. The principal 

 difficulty is to ascertain whether the animal under experiment is 

 moving in its normal fashion. Wilh the domestic and tame 

 kinds this is not considerable, but with wild species it requires 

 much patience and many attempts to secure the natural movement. 



On comparing some of the types of which chrono-photo- 

 graphic images have been obtained, very interesting analogies 

 are found. Thus, for locomotion on land, as well as in water, 

 it is possible to follow the gradual transitions between 

 simple reptation and the more complicated kinds of locomotion. 

 An eel and an adder put in water, progress in the same way ; a 

 wave of lateral inflexion runs continually from the head to the 

 tail of the animal, and the velocity of the retrograde progression 

 of this wave is slightly greater than the rate of movement of 

 the animal itself 



If an eel and an adder are placed on the ground, the manner 

 of reptation is modified in the same way with both species. 

 The undulatory movement has here and there a greater ampli- 

 tude, and this amplitude increases with the smoothness of the 

 surface on which the animal moves. 



With fish, provided they have fins, and with reptiles which 

 have feet, there remains, in general, a more or less pronounced 

 indication of the undulating movements of reptation. 



With the dog-fish, for instance, the retrograde wave which 

 goes the length of the body is very pronounced ; it is much less 

 with salmon, and exists hardly at all, except at the end of the 

 tail, with fish with thicker bodies. 



The retrograde wave during the terrestrial movements of the 

 Gecko is plainly visible, but is less pronounced with the grey 

 lizard and green lizard. 



The batrachians present, during the successive phases of 



1 Translation of a communic.-ition oy M. Marey to tlie Paris Academy of 

 Sciences. 



