March 13, 1879J 



NATURE 



435 



more species of Limicolce, and perhaps of other groups, 

 than I can here name. Is it to be supposed that all 

 these birds, some of them flying by night, make Bermuda 

 by the means which Dr. Weissmann considers sufficient ? 

 If his explanation is good it must be good for New 

 Zealand and Bermuda, as well as for the Mediterranean. 

 But there is yet a stronger case to be cited. The Sand- 

 Avich Islands, as I have learned on authority I cannot 

 doubt (though I know not any mention of the fact in 

 print), are yearly visited like Bermuda, but with even 

 greater punctuality, by large flocks of Golden Plovers — 

 whether C. virginicus or C. fulvus, is undetermined, but 

 that does not much matter. If the birds belong to the 

 first of these forms they must come from the west coast 

 of America, if to the second from the east coast of Asia. 

 Now there is no land between the Sandwich Islands and 

 the Califomian or the British- Columbian coast, but 

 between them and the Aleutians, as I learn from Mr. 

 Rye, there is one islet, Roca de Plata or Crespo. This, 

 however, does not lie in a straight line, and is some 720 

 miles north-west of the Sandwich Islands, and 1,200 

 south-west of the Aleutians. Running generally westward 

 of the Sandwich Islands is a series of islets, at distances, 

 perhaps, not exceeding 150 miles, which no doubt might 

 serve as guide-posts for the plovers did they but make for 

 them, but the series comes to an end in about long. 178° 

 W., and though by turning suddenly to the north-east 

 from Morell Island towards Mellish Bank (300 miles), 

 the Aleutians again appear as the nearest land in a 

 northerly direction, the distance of 1,020 miles has to be 

 covered ! On the supposition that the birds are of 

 Asiatic birth, and therefore come by another course, we 

 find that due west of Morell Island is Ganges Island, but 

 that is 930 miles off, and thence to reach the easternmost 

 of the Japanese group is 690 miles further I Thus, which- 

 ever form of golden plover it be that visits the Sandwich 

 Islands, its regular advent there needs, I think, some 

 fuller explanation than that afforded by Dr. Weiss- 

 mann' s theor)% 



Then again, there is another set of facts which seem 

 to me irreconcilable with the theory of mere "practice" 

 or "experience." It must be remembered that though 

 Dr. Weissmann relies most on the inherited practice of 

 the species, still he does not neglect the individual, 

 and both he and Dr. Palm^n make considerable use of 

 the observation that adults, and male adults In particular, 

 lead the migratory flocks. This fact, so far as I am 

 aware, has only been noticed in the northward movement 

 in spring, and elsewhere I have endeavoured to account 

 for it (" Encycl. Brit.," ed. 9, iii. p. 767). In autumn it 

 may be doubted whether there is anything of the kind, 

 and we have in many species, the young of the year — 

 birds that are but three months old, or even less, 

 migrating southward with the greatest regularity un- 

 accompanied by adults. This seems to happen with 

 nearly all the Acapiircs, nearly all the Limicolcp, and 

 perhaps, some others, that are bred in arctic or sub- 

 arctic districts. It happens also with our own Cuckoo 

 {Cuculus canortts), and this case is still more wonderful, 

 for the young Cuckoo has had no communication whatever 

 with its progenitors (who have already taken their de- 

 parture from our shores some weeks earlier), and its 

 foster-parents with us are generally species which do not 

 migrate to any great extent — the Hedge-Sparrow {^Accentor 

 moduiaris), Titlark {Anthits pratensis), and Pied Wagtail 

 {Motacilla lugubris). Yet our young Cuckoos, starting 

 alone and travelling over utterly unknown country, must, 

 on the whole, successfully reach their destination, or the 

 breed would become extinct here.^ Dr. Weissmann may 

 indeed well say of migrating birds, that the young, 



' Since I wrote this I have heard from Mr. Gatke, so ■well known for his 

 observations on migratory birds, that young Starlings pass over Helig )Iand 

 during July by hundreds of thousands, " without a single old bird accom- 

 panying them," while the old birds begin to migrate at the end of September 

 and continue for the next two months. 



when it cracks the shell, possesses •* great geographical 

 talent " ! 



I might easily prolong this article, for there is much 

 more to be said on the subject, and in some details, by no 

 means unimportant, Dr. Weissmann seems to have 

 fallen into errors that I have not here noticed, but my 

 chief object in making these remarks has been to hinder 

 persons who have not previously thought on the matter 

 from taking his easy explanation of the mystery of ornitho- 

 logical mysteries to be sufficient. Believing, as I once be- 

 fore said, that its solution is probably simple in the extreme, 

 and having a strong faith in the hereditary transmission 

 and accumulation of faculties so as to become a wonder- 

 working power, I yet cannot think that he has succeeded 

 in making known the secret and in satisfactorily explain- 

 ing how birds cross " the sacred spaces of the sea." 



Alfred Newton 



B' 



THE DIMENSIONAL PROPERTIES OF MAT- 

 TER IN THE GASEOUS STATE 

 Y assuming a sufficient number of sufficiently insig- 

 nificant individuals to constitute a group, it is 

 possible to imagine a state of things in which as far as it 

 can be observed from a certain distance, all evidence of 

 individual action is entirely lost. In this way has been 

 framed the molecular hypothesis or kinetic theory of gas. 

 But it must be obvious to every one who has considered 

 this molecular hypothesis, that the apparent imiformity in 

 the actions we perceive must be the result of the distance 

 (so to speak) from which these actions are observed, and 

 that could we sufficiently localise (as regards time and 

 space) our observation, we must perceive in all their 

 varieties the individual actions of the molecules. And 

 even failing this, between the actions of the individuals 

 and the absolute mean action there must be local or 

 parochial actions which would be distinguishable at 

 greater distances than the purely individual actions. 



In order that the properties of a gas may appear 

 perfectly uniform in all directions and quite independent 

 of the shape and volume of the space which the gas is 

 constrained to occupy, the number of molecules must be 

 countless, and the temporary action of each individual 

 must be confined to an imperceptibly small portion of 

 the space observed. If these conditions are not fulfilled 

 then the properties of the gas will not be uniform, and we 

 must have dimensional properties depending on the 

 dimensions of the constraining surfaces. 



The idea of our being able actually to perceive such 

 properties does not appear to have been entertained 

 hitherto. Until fifty years ago, all the mechanical pro- 

 perties of gases were regarded as quite uniform, the 

 only mechanical distinction between one kind of gas and 

 another being that of weight. Since that time in the 

 phenomena of diffusion, and the phenomena attending 

 the passage of gases through minute channels, properties 

 of gases have been recognised which readily distinguish 

 between one kind of gas and another, and even more than 

 this, for Graham found that there was a difference in the 

 relative behaviour of different gases in differing through 

 porous plates of different coarseness. Still, neither Gra- 

 ham nor anyone else appears to have recognised evidence 

 of dimensional properties. 



Neither did the development of the mathematical 

 theory lead to the revelation of dimensional properties. 

 Since 1864 it has been known that this theory included 

 the explanation of aU the uniform properties of gas. But 

 in developing this theory attention appears to have been 

 paid exclusively to the mean of the motions. And al- 

 though Prof. Maxwell points out that there must ultimately 

 be dimensional properties, he has not pursued the in- 

 vestigation, so as to reveal their character. 



In 1874 a very remarkable phenomenon was brought to 

 light by the experiments of Mr. Crookes — that in ex- 



