essay on the physiology of Laughter； in which he insists on 〃the general law that feeling passing a certain pitch； habitually vents itself in bodily action；〃 and that 〃an overflow of nerve…force undirected by any motive； will manifestly take first the most habitual routes； and if these do not suffice； will next overflow into the less habitual ones。〃 This law I believe to be of the highest importance in throwing light on our subject。‘
＇8＇ ‘The Senses and the Intellect；' 2nd edit。 1864； pp。 96 and 288。 The preface to the first edition of this work is dated June； 1855。 See also the 2nd edition of Mr。 Bain's work on the ‘Emotions and Will。'
＇9＇ ‘The Anatomy of Expression；' 3rd edit。 p。 121。
＇10＇ ‘Essays； Scientific； Political； and Speculative；' Second Series； 1863； p。 111。 There is a discussion on Laughter in the First Series of Essays； which discussion seems to me of very inferior value。
＇11＇ Since the publication of the essay just referred to； Mr。 Spencer has written another； on 〃Morals and Moral Sentiments；〃 in the ‘Fortnightly Review；' April 1； 1871； p。 426。 He has； also； now published his final conclusions in vol。 ii。 of the second edit。 of the ‘Principles of Psychology；' 1872； p。 539。 I may state； in order that I may not be accused of trespassing on Mr。 Spencer's domain； that I announced in my ‘Descent of Man；' that I had then written a part of the present volume： my first MS。 notes on the subject of expression bear the date of the year 1838。
All the authors who have written on Expression； with the exception of Mr。 Spencerthe great expounder of the principle of Evolution appear to have been firmly convinced that species； man of course included； came into existence in their present condition。 Sir C。 Bell； being thus convinced； maintains that many of our facial muscles are 〃purely instrumental in expression；〃 or are 〃a special provision〃 for this sole object。＇12＇ But the simple fact that the anthropoid apes possess the same facial muscles as we do；＇13＇ renders it very improbable that these muscles in our case serve exclusively for expression； for no one； I presume； would be inclined to admit that monkeys have been endowed with special muscles solely for exhibiting their hideous grimaces。 Distinct uses； independently of expression； can indeed be assigned with much probability for almost all the facial muscles。
Sir C。 Bell evidently wished to draw as broad a distinction as possible between man and the lower animals； and he consequently asserts that with 〃the lower creatures there is no expression but what may be referred； more or less plainly； to their acts of volition or necessary instincts。〃 He further maintains that their faces 〃seem chiefly capable of expressing rage and fear。〃＇14＇ But man himself cannot express love and humility by external signs； so plainly as does a dog； when with drooping ears； hanging lips； flexuous body； and wagging tail； he meets his beloved master。 Nor can these movements in the dog be explained by acts of volition or necessary instincts； any more than the beaming eyes and smiling cheeks of a man when he meets an old friend。 If Sir C。 Bell had been questioned about the expression of affection in the dog； he would no doubt have answered that this animal had been created with special instincts； adapting him for association with man； and that all further enquiry on the subject was superfluous。
＇12＇ ‘Anatomy of Expression；' 3rd edit。 pp。 98； 121； 131。
＇13＇ Professor Owen expressly states （Proc。 Zoolog。 Soc。 1830； p。 28） that this is the case with respect to the Orang； and specifies all the more important muscles which are well known to serve with man for the expression of his feelings。 See； also； a description of several of the facial muscles in the Chimpanzee； by Prof。 Macalister； in ‘Annals and Magazine of Natural History；' vol。 vii。 May； 1871； p。 342。
＇14＇ ‘Anatomy of Expression；' pp。 121； 138。
Although Gratiolet emphatically denies＇15＇ that any muscle has been developed solely for the sake of expression； he seems never to have reflected on the principle of evolution。 He apparently looks at each species as a separate creation。 So it is with the other writers on Expression。 For instance； Dr。 Duchenne； after speaking of the movements of the limbs； refers to those which give expression to the face； and remarks：＇16＇ 〃Le createur n'a donc pas eu a se preoccuper ici des besoins de la mecanique； il a pu； selon sa sagesse； ouque l'on me pardonne cette maniere de parlerpar une divine fantaisie； mettre en action tel ou tel muscle； un seul ou plusieurs muscles a la fois； lorsqu'il a voulu que les signes caracteristiques des passions； meme les plus fugaces； lussent ecrits passagerement sur la face de l'homme。 Ce langage de la physionomie une fois cree； il lui a suffi； pour le rendre universel et immuable； de donner a tout etre humain la faculte instinctive d'exprimer toujours ses sendments par la contraction des memes muscles。〃
Many writers consider the whole subject of Expression as inexplicable。 Thus the illustrious physiologist Muller； says；＇17＇ 〃The completely different expression of the features in different passions shows that； according to the kind of feeling excited； entirely different groups of the fibres of the facial nerve are acted on。 Of the cause of this we are quite ignorant。〃
＇15＇ ‘De la Physionomie；' pp。 12； 73。
＇16＇ ‘Mecanisme de la Physionomie Humaine；' 8vo edit。 p。 31。
＇17＇ ‘Elements of Physiology；' English translation； vol。 ii。 p。 934。
No doubt as long as man and all other animals are viewed as independent creations； an effectual stop is put to our natural desire to investigate as far as possible the causes of Expression。 By this doctrine； anything and everything can be equally well explained； and it has proved as pernicious with respect to Expression as to every other branch of natural history。 With mankind some expressions； such as the bristling of the hair under the influence of extreme terror； or the uncovering of the teeth under that of furious rage； can hardly be understood； except on the belief that man once existed in a much lower and animal…like condition。 The community of certain expressions in distinct though allied species； as in the movements of the same facial muscles during laughter by man and by various monkeys； is rendered somewhat more intelligible； if we believe in their descent from a common progenitor。 He who admits on general grounds that the structure and habits of all animals have been gradually evolved； will look at the whole subject of Expression in a new and interesting light。
The study of Expression is difficult； owing to the movements being often extremely slight； and of a fleeting nature。 A difference may be clearly perceived； and yet it may be impossible； at least I have found it so； to state in what the difference consists。 When we witness any deep emotion； our sympathy is so strongly excited； that close observation is forgotten or rendered almost impossible； of which fact I have had many curious proofs。 Our imagination is another and still more serious source of error； for if from the nature of the circumstances we expect to see any expression； we readily imagine its presence。 Notwithstanding Dr。 Duchenne's great experience； he for a long time fancied； as he states； that several muscles contracted under certain emotions； whereas he ultimately convinced himself that the movement was confined to a single muscle。
In order to acquire as good a foundation as possible； and to ascertain； independently of common opinion； how far particular movements of the features and gestures are really expressive of certain states of the mind； I have found the following means the most serviceable。 In the first place； to observe infants； for they exhibit many emotions； as Sir C。 Bell remarks； 〃with extraordinary force；〃 whereas； in after life； some of our expressions 〃cease to have the pure and simple source from which they spring in infancy。〃＇18＇
In the second place； it occurred to me that the insane ought to be studied； as they are liable to the strongest passions； and give uncontrolled vent to them。 I had； myself； no opportunity of doing this； so I applied to Dr。 Maudsley and received from him an introduction to Dr。 J。 Crichton Browne； who has charge of an immense asylum near Wakefield； and who； as I found； had already attended to the subject。 This excellent observer has with unwearied kindness sent me copious notes and descriptions； with valuable suggestions on many points； and I can hardly over…estimate the value of his assistance。 I owe also； to the kindness of Mr。 Patrick Nicol； of the Sussex Lunatic Asylum； interesting statements on two or three points。
Thirdly Dr。 Duchenne galvanized； as we have already seen； certain muscles in the face of an old man； whose skin was little sensitive； and thus produced various expressions which were photographed on a large scale。 It fortunately occurred to me to show several of the best plates； without a word of explanation； to above twenty educated persons of various ages and both sexes； asking them； in each case； by what emotion or feeling the old man was supposed to be agitated； and I recorded their answers in the words which they used。 Several of the expressions were instantly recognised by almost everyone； though described in not exactly the same terms； and these may； I think； be relied on as truthful； and will hereafter be specified。 On the other hand； the most widely different judgments were pronounced in regard to some of them。 This exhibition was of use in another way； by convincing me how easily we may be misguided by our imagination； for when I first looked through Dr。 Duchenne's photographs； reading at the same time the text； and thus learning what was intended； I was struck with admiration at the truthfulness of all； with only a few exceptions。 Nevertheless； if I had examined them without any explanation； no doubt I should have been as much perplexed； in some cases； as other persons have been。
＇18＇ 〃Anatomy of Expression；' 3rd edit。 p。 198。
Fourthly； I had hoped to derive much aid from the great masters in painting and sculpture； who are such close observers。 Accordingly； I have looked at photographs and engravings of many well…known works； but