8o 



NATURE 



[May 23, 1889 



Whilst the photographs furnish abundant material for 

 the further study and consideration of the normal move- 

 ments of a variety of animals and of man, there are some 

 in the series which are especially suggestive of new lines 

 of research. Amongst these are the series illustrating 

 locomotion in man in diseased conditions, such as loco- 

 motor ataxia, and lateral sclerosis. A distinct line of 

 scientific inquiry is suggested by those photographs which 

 represent men, women, or children, in the course of 

 movement which is associated with emotion. A new 

 chapter in Mr. Darwin's "Expression of the Emotions" 

 couldbewrittenby theaidof some of these series, and a most 

 interesting line of investigation, to be followed up by new 

 photographic analysis, is indicated. Not only is the play 

 of facial muscles connected with the series of emotions of 

 the base-ball player recorded in half a dozen pictures 

 taken between the moment of raising the bat and striking 

 the ball, but in other photographs we have unconscious 

 expression of mental condition exhibited by rapidly 

 transient movements of the whole body. These are 

 especially noticeable in the series of a na':ed child ap- 

 proaching a stranger in order to offer to her a bunch of 

 flowers, and in the three or four phases of movement of 

 the young woman springing from her bath after she has 

 been unexpectedly " douched ' from head to foot with a 

 bucket of ice-cold water. 



It is clear enough that the correlation of movements of 

 facial and limb muscles in the expression of emotion can 

 be best studied by such instantaneous photographic 

 series as the Muybridge publication contains ; and, as 

 Darwin, with his marvellous insight, showed, such study 

 of emotional states furnishes some of the most important 

 evidence with regard to the relationship of man and 

 animals. 



It is no doubt true that the immediate result of Mr. 

 Muybridge's work, from the scientific point of view, is the 

 desire which they evoke to apply this method systematic- 

 ally and experimentally to a variety of subjects of investi- 

 gation. The present pictures have great value, and many of 

 them great — indeed astonishing— beauty {e.j^. the wrestling 

 boys). They should be purchased by those who can afford 

 them for the purpose of bearing a share in the expense of 

 so important an experiment as that set agoing by the 

 University of Philadelphia. But we should like to see 

 the batteries turned on again, and a number of new sub- 

 jects investigated. Terrestrial locomotion has been 

 gradually developed through an amphibious transition 

 from aquatic locomotion. The movements of fishes, of 

 tadpoles, salamanders, turtles, and crocodiles should be 

 included in the scope of any study of vertebrate limb- 

 play. But even more necessary is it that in future the 

 scientific method, of theory, test hypothesis, and experi- 

 ment, should be followed in the application of the photo- 

 graphic batteries, so that each set of photographs may 

 definitely prove some particular point or points in the 

 orderly development of a general doctrine. 



For my own part, I should greatly like to apply Mr. 

 Muybridge's cameras, or a similar set of batteries, to the in- 

 vestigation of a phenomenon more puzzling even than that 

 of " the galloping horse." I allude to the problem of " the 

 running centipede." I have a series of drawings made from 

 large West Indian specimens which I kept alive for some 

 time in my laboratory at University College. At the same 

 time I made drawings and recorded as well as I could the 

 movements of the legs of Peripatus cafiensis, which was 

 also (through Mr. Sedgwick's kindness) living in my 

 laboratory. I am anxious to compare with these move- 

 ments the rapid rhythmical actions of the parapodia of 

 such Chastopods as Phyllodoce and Nephthys on the one 

 hand, and the curious "gait" of the Hexapod insects, of 

 which Prof Lloyd Morgan has already written a few 

 words in Nature. Passing on to scorpions and spiders, 

 and then to shrimps, lobsters, and crabs, we should 

 eventually possess the outlines of an investigation of 



Arthropod locomotion. There is no doubt that the Muy- 

 bridge battery would be the one effective means of study in 

 the case of the centipede and marine worms, although in 

 some cases a good deal may be done by intent observation 

 and hand-drawn records. The difficulty of this investigation, 

 and the disastrous results in the way of perplexity which 

 follow from too close an api)lication to it ■without the aid 

 of Mr, Muybridge, is set forth in certain lines, the author- 

 ship of which is unknown to me or to the friend who 

 kindly sent them to me on hearing that I was studying 

 the limb-play of centipedes. May I be pardoned for 

 quoting them, and associating in this way fancy with fact, 

 whilst expressing the hope that Mr. Muybridge will take 

 steps to prevent any such catastrophe in the future as 

 these lines record ! 



A centipede was happy— quite ! 



Until a toad in fun 



Said, " Pray which leg moves after which ? " 



This raised her doubts to such a pitch, 



She fell exhausted in the ditch, 



Not knowing how to run. 



E. Ray Lankester. 



ON THE DETERMINATION OF MASSES IN 



ASTRONOMY. 

 T N the An7iuaire du Bureau des Longitudes for 1889 

 ■*■ occurs an interesting article by M. Tisserand on the 

 methods employed in the measurement of the masses of 

 the heavenly bodies. The writer begins with an explanation 

 of the elementary principles leading to the law of Newton 

 that all bodies attract one another with a force which is pro- 

 portional to their masses and inversely as the square of the 

 distance between them. He proves, in a popular manner, 

 that this force is equal to the product of mass into 

 acceleration ; and therefore, speaking theoretically, to 

 compare the masses of two bodies it is only necessary to 

 apply directly to each of them the same force and to 

 measure the acceleration produced ; or, if a body be 

 placed in succession at the same distance from the sun 

 and the earth it will be attracted towards each with a 

 force which is proportional to their masses. Hence, 

 since the space traversed by a body is directly pro- 

 portional to the acceleration, if during the first second 

 the body fell 330 metres towards the sun, and i milli- 

 metre towards the earth, it would be obvious that the 

 sun had a mass 330,000 times greater than the earth. 

 Similarly, by applying the law of inverse squares, 

 the relative masses of the sun and earth might be 

 found when the distance of the body from each was 

 not the same. We find that the earth falls towards the 

 sun io-6o metres in a minute, and that our moon falls 

 towards the earth 4*90 metres in the same time. But the 

 earth is 386 times nearer the moon than it is to the sun, 



so correcting for difference of distance we get -\^,., = 



o"oooo328 metre as the fall of the moon towards the earth in 

 a minute. Therefore the sun's mass is to the earth's mass 

 as io'6 is to 00000328— that is, 1/323,000. This method 

 is, however, dependent on our knowledge of the distance 

 of the sun and moon. The same calculation may be 

 employed, without modification, to find the mass of a 

 planet having a satellite. Kepler's third law is used for 

 expressing the mass ?n of a planet in terms of the sun's 

 mass M. The formula being : — 



m _ (a' Y /T 



M ~ \a:) \V' 



where a is the semi-major axis of the planet's orbit 

 and T the time of revolution round the sun ; a' and T' 

 representing similar teims for the satellite. 



In the case of Jupiter-, observations of the four satellites 

 may be made and the mean result taken. A recent de- 

 termination by M. Schur gives the value 1/1047232 as. 

 compared with the sun. 



A 



