January, 1906.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



333 



to the non-breeding plumage of, say, the Waders, while the 

 brilliant livery worn during the greater part of the year really 

 answers to th3 breeding dress of the Waders, which is worn 

 for a short period only. But for the need of protection dur- 

 ing the period of quill-moulting it is contended the Mallard 

 would have assumed a permment breeding dress, as in the 

 case of the Sheldrake, or of the game-birds for example. 



Whenever the m.ale birds are brilliantly coloured we may 

 assume, he paints out, that this is a permanent breeding dress, 

 and when the hen stands in no need of a dull protective dress 

 she also assumes a similar plumage. 



With this interpretation we heartily agree. 



A New British Thrush. 



The Field, December 2, contains an account by Mr. T. 

 Whittal<er of the occurrence of the Duslcy Thrush ('J'urdiix 

 diihiiis) in Nottinghamshire. The bird was shot near Gun- 

 thorpe, and is described as having a flight like that of a jay, 

 and a note lil<e that of the fieldfare. This bird is a rare 

 straggler to Europe, having occurred but twice in Norway, 

 once in Germany, once in Belgium, and four times in Italy. 



Leach's Petrel in Berkshire. 



We learn from Messrs. Rowland Ward and Co. that they 

 have recently received a specimen of Leach's petrel in fine 

 condition, which had been obtained during the last week in 

 November at Caversham, having probably been driven inland 

 by the late strong westerly winds. It proved to be a male, on 

 dissection. 



PHYSICAL. 



3y Alfred W. PoRxiiK, B.Sc. 



Wireless Telegraphy. 



In the Annalen dcr Physik. J. S. Sachs describes experiments 

 which throw some light on the part which the earth itself 

 plays in wireless telegraphy. He conclades that transmission 

 is better the higher one is above the ground, and thence that 

 the earth is detrimental to the propagation of electric waves. 



Motors and Dust, 



Mr. W.K.Cooper has recently described experiments carried 

 out on a flour-covered track with a tricycle hauled along at 

 various speeds. A slack tyre is shown to raise more dust than 

 one pumped tight. A square box carried at different heights 

 above the ground raises less dust the higher it is above the 

 ground; very little is raised when the box is inclined so as to 

 ttirow the air down. 



Phosphorescence and Stokes' Law. 



Professors Nichols and Merritt, in the Physical Rcvicui for 

 October, describe experiments bearing on the phosphorescence 

 of Sidot blende (zinc sulphide) under various exciting causes. 

 Amongst other results they show that when the exciting light 

 is limited to a range of wave length from -470 to •497^, 

 the Inminescoucc observed after the exciting light is cut off 

 extends to wave lengths in the violet certainly beyond -46^. 

 There thus appears to be the same violation of Stokes' law 

 which they hive previously found to occur in the case of 

 fluorescence. In explanation of this statement we may 

 point out that, according to the law enunciated by Stokes, 

 the excited light nmst always be of longer wave length 

 than that which excites it. It would seem that under ordiuarv 

 circumstances this law must ba true whenever the radiation 

 depends merely upon temperature, as, for example, when dark 

 heat is focusscd upon a platinum black surface and makes it 

 white hot. O.i the other hand, it has been shown that even 

 in sucli a cas3 the result is due merely to the fact that the 

 region of maximum energy of the spectrum is situated for the 

 hottest known bodies in the infra red. If temperatures were 

 attainable so high that the maximum shifted into the ultra- 

 violet, the opposite to Stokes' law should be expected to 

 hold. 



When, however, the luminescence is not due merely to the 

 temperature — and such is the case for all kinds of phosphor- 

 escen;e and iluorescencc^there is no reason known why 



Stokes' law should hold; and we need not be surprised 

 therefore to find that it is not valid. It is of interest, more- 

 over, to point out that it has recently been shown that Stokes 

 himself threw doubt upon it in his later correspondence. 



R-efractivity of Fluorine. 



Messrs. Cuthbertson and Prideaux have succeeded in deter- 

 mining the refractive index of Fluorine. Special interest was 

 felt in regard to this question because of the relations which 

 Cuthbertson had previously shown to exist between the re- 

 fractivities of the elements. Taking the non-valent column 

 of elements as arranged in a periodic system of the elements, 

 he showed that their refractivities were in the following 

 ratios : — 



He Ne Ar. Kr Xenon 

 i I 4 5 10 ; 



he further, by obtaining data for other elements, proved that 

 these numbers appeared to be characteristic of the particular 

 rows in the Periodic Table to which these elements respec- 

 tively belong. Thus the value for sulphur (which lies in the 

 same row as .^rgon) is four times that for Oxygen (which lies 

 in the same row as Neon). Chlorine andBromine and Iodine 

 have numbers in the ratio of 4, 6 and :o. Now Fluorine heads 

 the column in which these numbers lie, and in order to prove 

 the generality of Cuthbertson's relations it was necessary to 

 find the value of Fluorine. As the result of a very difficult in- 

 vestigation carried forward with great zest by these investiga- 

 tors it turns out that this element also conforms to the rule. 

 As experiments on other substances are proceeding we mav 

 hope sliortly to bo able to classify other elements either as 

 conforming to this rule or to some more general one of which 

 it is a special case. Unfortunately the refractivities of com- 

 pounds, of which many are known do not supply much informa- 

 tion on this question, because the refractivities of compound; 

 are not the algebraic sum of the refractivities o; their constituent 

 atoms, although in most cases this additive law is approxi- 

 mated to within perhaps twenty per cent. We hope to return 

 to this matter before long in order to indicate the physical 

 cause of these simple relations between the refractivities 

 of the elements. 



ZOOLOGICAL. 



I>y R. Lydekker. 

 Colour Change in Gibbons. 



How imperfect is still our knowledge of the life-history of 

 many animals has been remarkably illustnited of late by a 

 gibbon from the Island of Hainan which has for some time 

 been living in the Zoological Society's Garden. When re- 

 ceived, and apparently full grown, it was jet black all over; 

 after a time, however, it changed its coat, when, to the astonish- 

 ment of everybody, it came out in a greyish buff livery, the 

 bare skin of the face alone retaining the original sable hue. 

 Probably certain allied species of gibbons undergo a similar 

 colour-change with age, although the Himalayan hulock and 

 the Sumatran siamang are apparently always black. 



Va-riation in Lizards. 



.•\ very remarkable paper on the pattern and colour variation 

 displayed by ditTerent phases of the wall-lizard of southern 

 Europe has recently been published in the Transactions of the 

 Zoological Society. How great are the variations in these 

 respects, a glance at the beautiful series of plates with which 

 the paper is illustrated will serve to show. By some authorities 

 these variations have been — and probably still are — considered 

 as of specific importance ; and it is from the boldness with 

 which the author, Mr.G. A. Boulenger, sweeps aw.ay such nominal 

 distinctions that we have ventured to call the paper remarkable 

 in these days of incessant splitting of species and races. " Of 

 late," writes the author, "a tendency has sprung up to greatly 

 multiply the species and thus destroy the old conception of 

 Lacerta muialis. I doubt whether such attempts will conduce 

 to a better understanding of the subject. . . . Characters 

 of form and coloration are given as distinctive which, on 

 examination of even moderately large series of specimens prove 

 to be worthless, while others of greater importance have been 

 overlooked or neglected." Evidently much water has still to 



