224 



NA rURE 



[January 5, 18Q9 



waler vapour, which of course wouKl be suMicient lo account for 

 that larf^e effect. 



Sir William Crookes mentions that, according to his ex- 

 periments, water vapour produces a greater conduction at very 

 low pressures than air ; but I decidedly disbelieve the difference 

 to be in any way similar to the numbers given by Mr. Brush, in 

 consequence of a rea.soning mentioned at the end of my Phil. 

 Max. paper, and I think the simplest explanation to be afforded 

 by this source of errors vitiating the pressure indications. 



It is no mere hypothesis but a certain fact that waler vapour 

 is f)eing evolved by heated gla.ss, and probably many other 

 substances. Sir William Crookes gathers quite a number of 

 arguments for it from his own researches, amongst others 

 spectroscopical proofs. The same opinion was put forward by 

 Kundt and Warburg, who were led to it by the very same sort 

 of experiments on conduction of heat as .Mr. Brush's, which . 

 they made as early as 1875 (Pos.^eiuioijf' s Annalcn,\'~fi, p.177). 

 Further investigations on the hygroscopical properties of glass, I 

 and on means for partially removing them, were published by 

 Warburg and Ihmori ( IViedcmaiin s Aiinalai, 27, p. 481). 



I cannot prove, of course, that there is no new gas evolved, 

 but I maintain that whatever facts Mr. Brush has put forward 

 as an evidence for its existence, can be explained quite simply 

 by the presence of water vapour (perhaps also other condensable 

 vapours), which he seems to have overlooked. I do not think it 

 necessary to go into details, and to analyse more thoroughly the 

 — rather fantastic— speculative part of the paper, where scarcely 

 any statement is not open to serious objections. 



Although thus I differ from Mr. Brush very much in respect 

 to the interpretation of his recent resvdts, I think his elaborate 

 experimental investigations, as reported in his Phil. Mag. 

 paper, to be of great value for the theory of these phenomena ; 

 certainly it would he very desirable that he might carry on those 

 researches, as he promised there lo do. 



-M. SmOI.UCHowSKI 1)E Smoi.an. 



\'icnna. University. 



The Curve of Life. 



TnK relationship between the duration of adolescence and 

 potential longevity in different species of mammals has repeatedly 

 been the subject of speculation. M. I'. Hourens, in his work 



£ 4- e 8-IO-l2t4.l 



on " Ilum.in Longevity," made the ratio between the two 

 periods as i to 5 ; Buffon had previously concluded that it was 

 as I to 7. In neither case were the data sufficiently numerous 

 and trustworthy to make these figures generally accepted. In 

 the course of some investigations on the variability of the adol- 

 escent period in different breeds of the same species among 

 certain well-known mamm.ils, I have satisfied myself that a re- 

 lationship exists between the duration of growth and the length 

 of an animal's natural life ; although it is evidently not of the ; 

 kind .suspected by the older writers. It may be stated as fol- 

 lows :— "The ratio of length of adolescence to length of life in the I 



NO. 1523, VOL. 59] 



shortest lived mammals is proportionally less than it is in longer 

 lived mammals. Kor example, the period of growth and de- 

 velopment of the domestic mouse is, according to my informant, 

 a breeder of these small rodents, about three nionth>. Its 

 natural lifetime is four years. In other words, the mouse may 

 be expected to live about fifteen times its adolescent period as 

 a mature animal. The Arab horse, according lo a well-known 

 authority, arrives at maturity in about eight years, its lifetime is 

 about forty years ; that is lo say, the animal lives four times the 

 length of its adolescence as an adult. Man, on ihe other hand, 

 who only completes his growth by the union of the sternal 

 epiphysis of the clavicle lo its shaft at the age of twenty-five, 

 has, after passing his fiftieth year, or " the middle arch of life," 

 to use Dr. Farr's phr.ase, only another twenty-five years' expect- 

 ation of life. His potential longevity accordingly foresh.adows 

 a period of maturity not greater than twice the length of his 

 youth. 



I have obtained, through the kindness of numerous corre- 

 spondents interested in breeding and rearing of farm and other 

 domestic animals, the approximate lengths of these two periods 

 in a few well-known mammals ; and the .iccompanying ili.igram 

 .shows the relations between growth and longevity among the 

 same animals plotted as a definite curve. This result was en- 

 tirely unexpected by me, and it may be interesting to some of 

 your readers. W. .Ainsi.ie Hiii.i.is. 



Hove. 



The Alleged Destruction of Swallows and Martins in 

 Italy. 



In your issue of December 22, 1898, I read the report of a 

 conference held by the Society for the Protection of Birds, at 

 which a paper was read on the decrease of swallows and martins 

 coming to Kngland, giving, as a reason for this decre.ise, the 

 netting of thousands of these birds on their arrival at the Italian 

 .shores, and their .subsequent consumption as food. 



M.iy I venture to remark that, during a residence of some 

 years in Italy, I have never once seen a swallow, or any 

 member of its family, exposed for sale, and that I have never 

 known, or heard ol. an instance of their being netted in 

 the manner described, though I am well acquainted with nearly 

 every part of the Peninsula. 



Since reading the above mentioned ac- 

 cusation against Italy, I have asked several 

 Italians whether they knew of such a 

 practice, and am informed that it is simply 

 nonexistent, the swallow being, perhaps, 

 the one bird in this country which is 

 regarded with a kind of sentiment by all 

 classes, as the harbinger of spring. 



Swallows, moreover, do not arrive on 

 these coasts in a state of exhaustion, and 

 to net them would be no easy feat. 



.\ few isolated cases of the cruel method 

 of capturing them with artificial flies 

 may occur, but not more so than in 

 England. 



"The Italian may be ruthless in his de- 

 structiim of other birds, but is certainly not 

 a destroyer of the Hiruitiiinidae. 



Of Ihe similar charge made .against the 

 French, I am not in a position to judge, 

 but I imagine that the cause for the 

 decrease ol the HiriiiuiiniJae in England 

 may lie in quite another direction, and 

 may be attributable to some equivalent 

 decrease of their favourite insects in our 

 iKiands, or in some atmospheric and cli- 

 matic change. Italy. I am convinceil, i< 

 not responsible in any way for it. Kn 11 \R1) Bauoi . 



Roma, December 27, 1898. 



st.s>'b)'C2'Ct'tt ct nn-M'X 



RADIATION PHENOAfENA IN THE 

 MAGNETIC FIELD. 



IN the spring of 1897 the scientific worUl became in- 

 debted to Dr. Zeenian for the observation that when 

 a source of light is placed in a strong magnetic field the 

 spectral lines of the light emitted by that source suflfer 



