56 



NATURE 



[Nov. 20, 1879 



elegance added would convey an idea of what the animal was 

 doing. 



I submit that the error which leads the experimenters so far 

 is forgetting that the mechanism of the human eye has as much 

 ith the matter as the movements of the horse's feet. 



Confining my argument to the gall ip, I contend that the con- 

 ventional extended attitude is true artistically, though it never 

 actually takes place whilst the horse is at this pace. The eye 

 (as is sufficiently proved by the need of machinery for finding 

 out the actual ' motions of horses' feet) does not obliterate and 

 receive impressions sufficiently quickly to trace the three paces 

 in the gallop; but it can note the fact that at some moment 

 during each bound, each of the four reach this extreme point. 

 Now the feet are twice as lung at this point as at any other, that 

 is to say, the passing out over and returning along thi 

 is for the eye a pause at the extreme. It is no more doubtful 



A Curious Rainbow 



I SEND yon a rough sketch of a curious rainbow gr m 

 Gareloch about 8.25 a.m. on October 20. I would have written 

 sooner but I delayed till I had obtained sketches from .several 

 different sources. I only saw the junction of the two I 



that a galloping horse should be painted as it usually is, than 

 that a swinging pendulum can only be suggested by drawing it 

 at one or other extreme "of its excursion. An artist could no 

 mire use Prof. Marey's diagrams in the way it is assumed he 

 should, tli in lie could represent a rolling wheel if he took no 

 liberties with the apparent position of the spokes ; but confined 

 himself by remembering their true places and numbers, which 

 of course are the same as when the wheel is at rest. 



It is true that a galloping horse might also be represented with 

 all its le„ r s gathered under it, but this is not done, because, as I 

 agree with Prof. Marey, " it is the artist's duty to add elegance 

 of form ; " whilst I dissent from him when he allows himself to 

 be convinced that "the greater part of the horses [of Phidias] 

 are represented in false attitudes " because the odograph says so. 



W. G. Simpson 



Edinburgh, November 12 



that being the only part of Row Bay visible from my standpoint, 

 but several observers saw the whole group as I have drawn it. 

 The sea was quite glassy, so that the inverted rainbow A must 

 have been formed by the sun's rays reflected from the water. 

 The wind was just beginning to rise and some scudding showers 

 were passing up from the Firth of Clyde from the south-west, 



Road to Kilcreggan. 



Roseneath. Row Point. Pier. 



but the bay was quite calm. The bow D was perfectly full and hills seen such a combination of rainbows, I think .the description 



bright, while B died away at its highest point. I can only may have some interest for some of your readers. The hill to 



imagine that B was formed by light reflected by some bright th? right is Knapps Hill, and is 2,000 feet high and three and a 



cloud, but I did not observe any bright enough. The view is half or four miles distant. J. B. Hannay 



nearly north-west. As I have never even among our Scottish Woodbourne House, Helensburgh, November 4 



How Snakes shed the Skin 



In Nature, vol. xx. p. 530, Dr. H. F. Hutchinson, amid 

 some interesting facts about snakes, says : "I have never wit- 

 nessed the process of skin-shedding, nor, I believe, has any 

 observer." The Doctor then ventures an ingenious, though 

 incorrect, hypothesis of his own. In the American Naturalist 

 for January, 1S75, i.e., vol. ix. No. I, under the title, "The 

 Pine Snake of New Jersey," I gave an article embodying the 

 results of several years' study of Pituophis mclanoltucus, in which 

 the process of exuviation is described as witnessed by myself. 

 Herewith is an abstract. The few words interpolated for the 

 sake of clearer exposition are put in brackets. 



Near the close of Septemher, 1S73, at I p.m., looking into 

 the box, I saw that the female snake had started the skin from 

 her head. It was a little torn at the snout, and I found that 

 the head and a little of the neck were denuded. The denuding 

 process was going on, but very slowly. Doubtless the chief 

 difficulty was in starting the skin, and I felt sorry that I did not 

 see the start. The neck was very slowly becoming divested of 

 the old cuticle, which, at first glance, had a sort of back-creeping 

 aspect. What surprised me was the fact that there was not the 

 least friction in the process ; that is, there was no rubbing against 

 any exterisr object. It really did look as if an invisible power 

 was drawing the skin back upon itself. [Looking closely, I 

 caught the secret. There was a systematic alternate swelling of 

 the body at the neck of the skin, thus stretching it, and making 

 a shoulder in front of the neck, each swelling pushing the 

 loosened skin a little backward.] The old skin at this time is 

 very moist and soft, and any swelling of the body stretches and 

 liosens it. So soon as the exuviation has reached the part of 

 the body containing the larger ribs, this doffing of the old suit 

 proceeds more rapidly, and with a singular system. It is done 



just in this way : Exactly at the place where the skin seems to 

 be moving backward, a pair of ribs expands. This action 

 enlarges or puffs out the body, and by stretching loosens the 

 skin at that place. In this movement both ribs in the pair act 

 at the same time, just as the two blades of the scissors open 

 together. Xow comes a second movement of this pair of ribs, 

 in which action the two ribs alternate with each other. One of 

 them— say the one 011 the right side — is pushed forward and 

 made to slip out of and in front of the constriction made by the 

 swelling, when it immediately works backward, that is, against 

 the neck of the double receding skin. Now the left rib makes 

 a like advance, and in a similar manner presses backward. 

 [Thus for every increment of exuviation, or backward movement 

 of the inverting skin, three actions occur with rhythmic method; 

 the expanding of one pair of ribs, the intumescence of the body 

 at ih.it spot, and the pushing back of the skin by the alternate 

 action of each rib.] Thus the final action of each pair of ribs 

 is not synchronous, but alternate, and has a notable sameness of 

 1 and result with that of the alternate hitching of each 

 side of the mouih when swallowing a large prey. Indeed, 

 swallowing, with a serpent, is a misnomer, for that laborious 

 hitching is not more a pushing of the prey down the gullet than 

 a drawing of the body over it. The Western man said he always 

 felt better after getting himself round a good beef-steak. With 

 the serpent this is a literal fact; it puts itself outside of its 

 victim. So with that singular costal action it seems to push the 

 skin backward ; but this is an illusion, for it actually pushes 

 itself forward, pulling the skin out as itself advances out of the 

 shin, thus with each movement or advance lengthening the 

 inverted cuticle behind ; that is, the old hose everts or 

 evolves itself forward, though it appears as if by some occult 

 force to be pulled on itself backward. 



