246 



NATURE 



{Jtily 26, 1877 



from its surface, but then so strongly that under no 

 circumstances whatever can any body come into actual 

 contact with it. 



This appears to be the only constitution we can 

 imagine for a rigid-elastic body. And now that we have 

 got it, the best thing we can do is to get rid of the rigid 

 nucleus altogether, and substitute for it an atom of 

 Boscovich — a mathematical point endowed with mass 

 and with powers of acting at a distance on other atoms. 



But Boltzmann's molecules are not absolutely rigid. 

 He admits that they vibrate after collisions, and that their 

 vibrations are of several different types, as the spectroscope 

 tells us. But still he tries to make us believe that these 

 vibrations are of small importance as regards the principal 

 part of the motion of the molecules. He compares them 

 to billiard balls, which, when they strike each other, 

 vibrate for a short time, but soon give up the energy of 

 their vibration to the air, which carries far and wide the 

 sound of the click of the ball?. 



In like manner, the light emitted by the molecules 

 shows that their internal vibrations after each collision 

 are quickly given up to the luminiferous ether. 



If we were to suppose that at ordinary temperatures 

 the collisions are not severe enough to produce any 

 internal vibrations, and that these occur only at tempera- 

 tures like that of the electric spark, at which we cannot 

 make measurements of specific heat, we might, perhaps, 

 reconcile the spectroscopic results with what we know 

 about specific heat. 



But the fixed position of the bright lines of a gas 

 shows that the vibrations are isochronous, and therefore 

 that the forces which they call into play vary directly as 

 the relative displacements, and if this be the character 

 of the forces, all impacts, however slight, will produce 

 vibrations. 



Besides this, even at ordinary temperatures, in certain 

 gases, such as iodine gas and nitrous acid, absorption 

 bands exist, which indicate that the molecules are set 

 into internal vibration by the incident light. 



The molecules, therefore, are capable, as Boltzmann 

 points out, of exchanging energy with the ether. 



But we cannot force the ether into the service of our 

 theory so as to take from the molecules their energy of 

 internal vibration and give it back to them as energy of 

 translation. It cannot in any way interfere with the 

 ratio between these two kinds of energy which Boltzmann 

 himself has established. All it can do is to take up its 

 own due proportion of energy according to the number 

 of its degrees of freedom. 



We leave it to the authors of the " Unseen Universe " 

 to follow out the consequences of this statement. 



J. Clerk Maxwell 



OUR BOOK SHELF 



Report on Ihc Proi^rcss and Condition of the Royal Gardens 



at Kcw diiriiii; the Year 1876. (Clowes and Sons.) 

 Sir Joseph Hooker's annual report on the Royal 

 Gardens, Kew, for 1S76, has just been issued. It is a 

 pamphlet of some thirty-three pages, and is a consider- 

 able improvement on the leports of former years. It 

 deals most fully with new plants of economic interest, 

 whether such have been actually received or sent from the 

 Royal Gardens, or have formed the subject of correspon- 



dence with foreign or colonial governments. It is 

 eminently satisfactory to [know that such useful plants as 

 the Para rubber {Hevca brasiliensis), the ipecacuanha 

 (CcpluTlis ipecacuanha), the Liberian coffee {Coffea 

 liberica), and others, have been most successfully 

 introduced into India and other countries, through the 

 instrumentality of Kew. Of the 70,000 seeds of the 

 HcTca received at Kew about the middle of June last 

 year, all of which we are told were at once sown, and 

 though closely packed together, covered a space of over 

 300 square feet so soon as August 12th following, upwards 

 of 1,900 living plants, raised from these seeds, were 

 transmitted to Ceylon in thirty-eight Wardian cases, 90 

 per cent, of the whole consignment reaching Dr. Thwaites 

 in excellent condition. So rapid was the germination of 

 these seeds at Kew that some had actually started into 

 growth on the fourth day alter sowing, and many in a 

 few days reached a height of eighteen inches. It has 

 been arranged that these young plants shall " be nursed and 

 established in Ceylon for subsequent transmission through 

 the Indian Gardens to Assam, Burma, and other hot damp 

 provinces of India proper." Besides those sent to India, 

 smaller quantities of plants have also been despatched to 

 the west coast of Africa, Burma, Dominica, Jamaica, Java, 

 Queensland, Singapore, and Trinidad. With regard to 

 ipecacuanha, though Dr. King reports that he fears it can- 

 not be grown so far north in 1 ndia as Bengal, it is neverthe- 

 less in some situations capable of rapid and extensive culti- 

 vation, and the roots grown in India have been proved to 

 be quite as efficacious in a medicinal point of view as those 

 from the best districts of South America. In the matter 

 of Liberian coffee, the wide and general extension of this 

 new kind in coffee-growing countries bids fair, in many 

 parts, to entirely supersede the old and better known 

 Coffea arabica. Sir Joseph Hooker reports the receipt of 

 numerous favourable notices of the plant, and quotes 

 " two from opposite sides of the world," namely Ceylon 

 and Dominica. With reference to diseases affecting 

 coffee plants — which it is hoped the more sturdy habit of 

 the Liberian kind will help it in some measure to resist — a 

 very exhaustive notice is furnished, which is not only of 

 much interest in a scientific point of view, but cannot fail 

 to be valuable to coffee-planters themselves. It will, 

 moreover, no doubt be the means of causing more careful 

 observations to be made by residents on cotfee estates or 

 in coffee-growing countries into the nature and habits of 

 diseases which are still more or less obscure. 



Considerable additions are reported to the Museums and 

 Herbarium, the new building for the accommodation of 

 the latter collection being now in a very advanced state. 

 The new Laboratory, which has been erected at the 

 expense of T. J. Phillips Joddrell, Esq., is reported as 

 having been completed during the year, and though not 

 fully provided with the necessary equipment at the time 

 the report was written, has been already, as our readers 

 are aware, used by Dr. Tyndall in several of his recent 

 experiments and researches. 



Two new features of the report which we have not 

 already mentioned are — first, the introduction of plates, 

 one being a figure of the new Liberian coffee plant, and 

 the other a view and ground-plan of the Laboratory ; 

 and second, the publication of the report, at a charge of 

 sixpence, by Messrs. Clowes and Sons. 



Natural History Transactions of Northumberland and 

 Durham, vol. v., part 3. (Williams and Norgate, 

 1S77.) 

 This part is by'^no means the least valuable of these 

 transactions ; on the contrary, it will rank high, owing to 

 the contributions of Dr. Embleton and Mr. Atthey on 

 the structure of the Labyrinthodonts, and the eight excel- 

 lent plates by which their papers are illustrated. The 

 illustrations of Loxomma and Anthracosaunis are as 

 complete and instructive as any that, have yet been pub- 



I 



