424 



SCIENCE. 



[Vol. II., No. 34. 



as usual, continues an air-passage to the phar- 

 \"nx, opening at tlie back of the hard palate bj' 

 a median orifice in common with its fellow. In 

 sizable skulls, as of a raven, hawk, or eagle, a 

 bristle or even a wooden toothpick readily trav- 

 erses the conduit which runs between the basi- 

 sphenoid and the underlying basi-temporal. 

 This whole passageway-, from outer ear to 

 tympanic cavity, and thence through eustachian 

 tube to pharj-nx, represents the persistentl}^ 

 patulous part of the first post-oral visceral 

 cleft of the embryo, onlj- occluded by the mem- 

 brana tj-mpani. Near the eustachian orifice 

 are observed two definite openings. The 

 anterior and superior of these is the fenestra 

 ovalis, fitted, as usual, with the foot of the 

 stapes, as seen in fig. 1, closed by membrane, 

 which further occludes this opening into the 

 vestibular cavitj'. The other is the fenestra 

 rotunda, similarlj' leading into the cocJdear 

 cavitj'. The two are generally close together, 

 separated merelj' by a bony bridge or bar. 

 The former lies always in the obliterated 

 suture between the prootic and opisthotic ele- 

 ments of the petrosal bone, the latter wholly 

 in the opisthotic; both are thus as in man. 

 Close examination at a point somewhere about 

 the fenestra ovalis will discover a minute fora- 

 men, corresiDonding to the human ' stylo-mas- 

 toid foramen ' inasmuch as it represents the 

 orifice of exit of the seventh cranial nerve 

 (' portio- dura') from the petrosal bone, here 

 in the cavitj- of the middle ear, there being 

 none such upon the outside of the skull. Thus, 

 in the drj' skull of a bird, the hard p)arts of the 

 tympanic cavitj-, including the eustachian tube, 

 can readilj' be inspected from the outside ; even 

 the limits of the prootic and opisthotic bones 

 can be determined by the site of the fenestra 

 ovalis, and the ossicula auditus be seen in situ. 

 To see these things in the human or anj- ordi- 

 narj' mammalian ear, requires special prepara- 

 tions, as thej' lie in a tympanum which is itself 

 at the bottom of a contracted tube. Details of 

 mere size and shape aside, the above general de- 

 scription of the passageways will applj' prettj' 

 ■well to any bird, and should suffice for recogni- 

 tion of the parts ; though the number and 

 varietj' of the irregular pneumatic openings 

 (comparable to those of the human mastoid 

 cells) may be puzzling at first sight. 



(,To be continued.) 



ON THE KINETIC THEORY OF THE SPE- 

 CIFIC HEAT OF SOLIDS. 



In a paper entitled ' Kinetic considerations 

 as to the nature of the atomic motions which 



probabl}' originate radiations,' ' the writer has 

 given reasons in support of the hj'pothesis that 

 different chemical atoms are all composed of 

 the same kind of ultimate atoms, which are iu 

 ever}- respect equal and similar. Reasons were 

 also given, tending to show that the vibrations- 

 of these ultimate atoms originate luminiferous 

 and thermal radiations. And further, suppos- 

 ing radiations to originate in the vibrations of 

 eciual and similar ultimate atoms which are set 

 in vibration bj- the collision of moving mole- 

 cules, an attempt was made to prove that two 

 unlike masses of gas which are in thermal 

 equilibrium b}' radiation will also be so wherk 

 mixed ; i.e., v»'hen the equilibrium depends up- 

 on the collisions of the molecules rather than 

 upon radiation. 



• The object of the present paper is to consider 

 the probable ph}-sical state of solid bodies, es- 

 peciallj' as to the amount of energy' distributecl 

 among the different degrees of freedom possi- 

 ble in such bodies, and to show that the same 

 h^'pothesis of equal ultimate atoms would cause- 

 solids which are in thermal equilibrium b}' ra- 

 diation to be also in thermal equilibrium when 

 brought into contact, i.e., when the equilibrium 

 depends upon the collisions of the molecules. 



Let us notice, in the first place, what is ap- 

 parently the mechanical significance of Dulong- 

 and Petit's law, which maj- be stated thus : 

 the amount of heat which must be imparted 

 to a chemical atom of a simple solid bodj- to- 

 increase its temperature one degree is approxi- 

 matel}' the same for all the elements. Neu- 

 mann has further shown, that, for compound 

 solids, those of similar chemical composition 

 require approximately the same amount of 

 heat per chemical atom, but the amount is less 

 than for simple solids. There are, however, 

 a' ver}- few unexplained exceptions to these 

 laws, which are due possiblj" to uncertaint}' as 

 to atomic weights. 



The mechanical explanation of these experi- 

 mental laws seems to be contained in the 

 statement, that, in simple solids, cohesion and 

 chemism are one and indistinguishable ; or, ta 

 express it otherwise, we may saj- that the mole- 

 cules of simple solids are monatomic,the cohe- 

 sion being, of course, much greater in some- 

 solids than in others. 



That this is a correct conception of the rela- 

 tions of the atoms of a simple solid, is made 

 probable b}^ various facts, among which this 

 maybe mentioned, — mercurj' and cadmium, 

 which are known to be monatomic as gases, as 

 solids fulfil Dulong and Petit's law, and are 

 therefore in the same physico-chemical state 



^ Science, ii. 76. 



