July 4, 1878] 



NATURE 



255 



subject, the true mathematical expression for the velocity 

 ot the wave in terms of that of the molecules of the gas has 

 been determined by Prof. Maxwell. The expression is — 



Velocity of wave equals — ^ into the velocity of the mole- 

 cules. This expression requires a slight additional cor- 

 rection in the case of most gases, owing to the movements 

 of rotation developed at the collisions of the molecules, 

 depending on their more or less irregular shape, which 

 rotation calculably must delay the wave to a certain 

 extent. According to the experimental results of Kundt 

 and Warburg, the above expression for the velocity of 

 sound in terms of that of the molecules holds exactly true 

 (without correction) for vapour of mercury (whose mole- 

 cules, it might perhaps be remarked, are simple or mona- 

 tomic). The slight deviations from the above constant 

 for the velocity of the wave that one observes in fact, are 

 quite consistent with what one would expect from theory. 



13. It may be observed that all the usual apparatus for 

 illustrating sound-waves of course applies to the kinetic 

 theory, as such apparatus is only intended to show the 

 effect produced on the mass of air, or the condensations 

 and rarefactions, without exhibiting the molecular me- 

 chanism that underlies it. A true view of the mode of 

 propagation of the wave and the manner in which the 

 condensations and rarefactions are produced at its pas- 

 sage, can only be obtained by visualising the fact that 

 the molecules of gas are in motion in the normal state of 

 the gas, in accordance with the accepted kinetic theory 

 of gases.^ 



14. The kinetic theory thus reduces the conditions on 

 which the velocity of sound in a gas depends to one, viz., 

 the velocity of the molecules of the gas. It is not, however, 

 this simplification^alone that should recommend it, for it 

 is not a mere question of choice or preference of one 

 view over another, but a question of fact. For a theory 

 of the conditions physically affecting the velocity of 

 sound and its mode of propagation that may apply to one 

 view as to the constitution of a gas (viz., the old view 

 where the molecules are supposed at rest), cannot possibly 

 apply to the diametrically opposite view of gaseous con- 

 stitution represented by the accepted kinetic theory. It 

 would appear desirable and fitting that the kinetic theory, 

 having been applied so generally in other respects, 

 should find a general application to so important and 

 fundamental a fact affecting a gas as the propagation of 

 sound in it. 



1 5. Since the physical basis of a system is admittedly 

 the most important of the whole, it would appear reason- 

 able to expect that the investigation of problems in 

 acoustics might gain by regarding the propagation of 

 sound on the true physical basis represented by the 

 accepted kinetic theory of gases ; or by taking a true 

 physical basis to ground the investigations upon, instead 

 <rf" one (based upon the old view of gaseous constitution) 

 that admittedly does not harmonise with the facts. 



Note. — It has recently come to my knowledge that 

 two papers have been lately pubUshed on this subject, 

 one by Prof. Roiti, of Florence {Nuovo Cimento, 1877), 

 the other by Prof. J. H. Hoorweg {Archiv Neer.,ya., 1876), 

 a brief abstract of which also appears in Beibldtter zu 

 den Annalen der Physik und Chemie (vol. i. part 4, 

 p. 209, 1877). Though the latter of these papers appears 

 to precede mine {Phil. Mag., June, 1877), I may add that 

 a sketch of the same theory appears in a little book 

 (" Physics of the Ether," E. and F. N. Spon), pubUshed 

 by me in 1875. There is also an interesting paper by 

 Mr. J. J. Waterston {Phil. Mag., 1859, supp. to voL 16), 

 in which he proposes to illustrate the propagation of 



' It would appear not unreasonable to conclude that a realisation of the 

 nioleoilar basis underlying the propagation of sound, according to the accepted 

 kiuetic theory, might be able to throw sim; light on the investigations in 

 connection with the telephone and other allied instruments, where the mole- 

 cular basis of the phenomena would seem to be the essential point to be 

 considered. 



I 



waves by a system of spheres, but he does not go into 

 the explanation as to how the motion he assigns to the 

 spheres can properly represent the case of a gas in its 

 normal state. There are, nevertheless, points of interest 

 in the paper. 



S. ToLVER Preston 



WHAT IS MORPHOLOGY f^ 



IF those of us who have laboured up the hill of life 

 - revert to the studies of our youth, I think we shall 

 not remember to have heard our teachers speak of the 

 " Morphology of Animals." I cannot remember when or 

 where I first met with the word ; although the idea itself 

 with regard to plants, has been familiar to me for nearly 

 forty years, that is, since the time when I became pos- 

 sessed of " Lindley's Introduction to Botany ; " but he 

 used the term " Organography." The term " Morphology " 

 was used by Schleiden in his "Principles of Scientific 

 Botany " at least thirty years ago ; and I may say in 

 passing that the study of that work was one of the best 

 preparations I received for the work I have undertaken 

 since. 



A comparison of the mode in which both plants and 

 animals are developed was suggested to me, if not for the 

 first time, yet then with new force, by reading Johann 

 Miiller's " Physiology of Man ; " especially in the part on 

 Generation, and more especially in his statement of, and 

 criticisms upon, Caspar J. Wolff's "Theory of Gene- 

 ration," which was published at Halle in 1759. The very 

 mention of this date is interesting, for this is evidently 

 the time, and this work of Wolff's was surely the work, 

 which suggested to the great, rich mind of Goethe the 

 idea of an underlying unity amid all the diversity of 

 vegetable and animal forms. How fruitful this conception 

 of the simplicity and unity of vegetable and animal 

 patterns has been, I need not tell you ; for more than a 

 century it has been yielding precious and ever increasing 

 results. It was natural, therefore, that a division ot 

 biology so new and so fascinating, should gain for itself a 

 name : and as naturalists had been from time immemorial 

 famiUar with the metamorphosis of certain types, the term 

 "morphology" which especially treats of such changes in 

 the individual life-history of a plant or of an animal, was 

 natural, easy, and appropriate. 



The h priori dreams which made the study of vertebrate 

 morphology appear transcendental, and indeed gave it 

 that title as a cognomen, caused great loss of time and 

 of talent : and if Prof. Huxley had done nothing else 

 whatever than dispel the glamour of these dreams, he 

 would have deserved well of his age. His " Croonian 

 Lecture," delivered at the Royal Society about twenty 

 years ago, was as " a trumpet that gives a certain sound ; " 

 the dreamers awoke from their dreams, and became the 

 workers, who since that time have wrought with labour 

 and travail night and day. But the science of morphology, 

 which had become an elegant pastime here, had long 

 before Prof. Huxley's time found a noble band of 

 workers in Germany ; from that land came the dream ; in 

 that land arose the workers ; the labours of Rathke, von 

 Baer, and Reichert were ready to the hand of our biolo- 

 gical reformer. After these, who were the chiefs of the 

 band, came others, all men of name and renown ; " but 

 they attained not to the first three." 



My own indebtedness is primarily to Johann Muller, 

 who in his " Physiology of Man," already referred to, gave 

 such an excellent abstract of the labours of the embryo- 

 logists, his countrymen. I ought not to forget his lamented 

 translator, Dr. Baly ; for in the original Miiller's work 

 was a sealed book to me, and indeed would be now. 



The fact that all organic beings pass through variousr 

 stages, and run a certain round of life, is now becoming 



' The first of a course of lectures " On the Morphology of the Batrachia," 

 delivered at the Royal College of Surgeons, by Prof. W. K. Parker, F.R.S. 



