40 



NATURE 



[May 21, 1874 



step," do exactly the opposite, that is, place the opposite 

 feet forward simultaneously ; we then have the following 

 formula : — ■ 



All will recognise this as the " trot " in the horse ; 

 although, as M. Marey has proved, there is always, in the 

 true " trot," an interval between each of its two elements, 

 during which all the feet are off tlie ground at once, 

 thus : — 



the upper of the last two formute, however, represents 

 the walk of the elephant exactly. 



In the amble and the trot, therefore, each complete 

 series of steps is formed of two parts which never 

 overlap ; it follows that the sounds produced by them 

 are double also. 



The walk of the horse is a phenomenon a little more 

 difficult to reahse at first sight. Again referring to the 

 two men, suppose that they walk quite out of step, as it 

 may be termed, in such a way that the front one has 

 raiscd\i\^ right leg at the same moment that the hind one 

 is Just raising his, although they keep to the same number 

 of steps. Such being the case the sequence of the steps 

 would be right fro7it, left hind, left front, and right hind, 

 which is the order of succession in the horse, and may be 

 represented thus : — 



horse, given above, it is evident that the representation is 

 correct, except in a very slight point, which is that the 

 right hind leg is on the ground, though just on the point 

 of leaving it, whereas it ought to be just off it, because in 

 walking there are never more than two legs on the ground 

 at the same time. The general direction of the legs is 

 quite correct. If the animal had been " ambling," the 

 left hind-foot would have been off the ground, as well as 

 the left fore. It is quite impossible to mistake the 

 " walk " for the " trot," if their formulae are compared and 

 the positions at any given time worked out from them. 



A. H. Garrod 



In this formula it is seen that at no time arc there more 

 than two feet on the ground at the same moment, and M. 

 Marey states that in his numerous experiments such is 

 always the case, except when a load is being taken down 

 an incline in a wheeled vehicle, on which occasion three 

 feet may be on the ground simultaneously. In the walk 

 of the horse there are therefore four sounds produced in 

 each complete series of steps, and these four are at equal 

 or nearly equal intervals of time. 



We are now in a position to judge of the accuracy of 

 Miss Thompson's delineation of the " Roll Call horse," 

 which is represented walking, with the left fore -foot fully 

 raised from the ground, whilst the others are on it. The 

 right fore-leg is nearly perpendicular and not bent ; that 

 is, about half-way between the commencement and the 

 end of its step. The left hind-foot is somewhat in 

 front of the perpendicular axis of the leg ; that is, has 

 just commenced its step ; and the right hind foot, though 

 on the ground, is on the point of leaving it. As the animal 

 is -walking, the lengths of the steps and of the intervals 

 must be represented, as shown above, as of equal dura- 

 tion, and the following is its expression, the thick vertical 

 line representing the moment at which the painting 

 figures it : — 



By comparing this with the formula of the walking 



CARPENTER'S "MENTAL PHYSIOLOGY" 



Principles of Mental Physiology. By W. B. Carpenter, 

 M.D., F.R.S. (Henry S. King & Co.) 



THE title of the volume before us shows that its 

 author is one of those philosophers — happily, an 

 increasing number — who refuse to treat the phenomena 

 of mind as though they were in no way connected with 

 the body through which they find their expression. Mental 

 I Physiology is a comparatively new science, and does not 

 ! date further backward than the days of Hartley. Before 

 I his time, and to some extent since. Physiology has been 

 : treated from what — to employ a word too often pressed 

 1 into the service of a somewhat hazy idea — may be called 

 i the metaphysical point of view. The phenomena of mind 

 have been abstracted from all their surroundings, and 

 have been analysed by themselves, and the result has 

 naturally been that we have been left but little wiser than 

 before. Dr. Carpenter rejects this method, and bases his 

 Psychology on the construction and working of the ner- 

 vous system. But while shunning the metaphysical treat- 

 ment of the subject, he does not adopt the other extreme, 

 the doctrine, we mean, of the thorough materialist, who 

 regards all mental phenomena without exception as the 

 outcome of previous physical causes, which necessarily 

 produce certain results. He steers a middle course, inas- 

 much as, while he advances the theory " of the dependence 

 of the Automatic activity of the mind upon conditions 

 which bring it within the nexus of Physical Causation," 

 yet he believes in " an independent power, controlling and 

 directing that activity, which we call Will." 



This doctrine of the independence of the Will is the 

 distinguishing characteristic of Dr. Carpenter's philosophy 

 in the book before us ; it runs through the entire work as 

 the one grand exception among a series of physical 

 sequences, interdependent, and standing to each other in 

 the relation of cause and efi'ect, of antecedent and conse- 

 quent. Yet, even to a mind which is not " trammelled by 

 system," this splendid anomaly may seem strange and 

 surprising, though the prevalence of the belief in a Free 

 Will, even among scientific thinkers, need cause no wonder, 

 so long as the ethical bias is not rigidly excluded from psy- 

 chological speculation. It is the meritorious timidity of 

 the moral side of human nature which says, " whatever 

 else may be under laws of necessity, the Will at least is 

 free and independent, for the alternative doctrine deprives 

 all actions of their moral value, and reduces man to the 

 level of a mere machine." 



It is clear that Dr. Carpenter is not satisfied 

 with the doctrine of the so-called necessarian school 



