200 



NA TORE 



[December 29, 1892 



name, and anything i^jthey knew about it One of these, a 

 Galway woman, spea ^ng Irish better than English, gave me 

 the name in her laiigu ge (which I won't attempt to transcribe, 

 for it was a very lung one), and also said that the animals were 

 well known to jump down people's throats to their certain de- 

 struction. C. BUSHE. 

 Athenaeum, December 24, 



The Great Ice Age. 

 There is in the Astronomical theory of the Ice Age a point 

 of some importance, not mentioned by Sir R »bert Ball in his 

 interesting work on this subject, to which I invite the reader's 

 attention. I mean Ihe slowness with, which the difference 

 between the length of itiminer and that of winter is varying in 

 the neighbourhood of its maximum. 



To compute this ditference and its mean value, we put 



a = the mean distance of the earth from the sun, 



e = the eccentricity of the earth's orbit, 



CO = the longitude of the perihelion of the earth's orbit, 



T = the length of the year in mean solar days, 



A = the difference between the lengtbs of the two seasons in 



mean solar days, 

 7) = the mean value of this difference during the interval 

 between the two dates, corresponding to a = w^ and 



Then, the eccentricity remaining always extremely small, the 

 difference between the areas of the two segments in which the 

 line of the equinoxes divides the earth's orbit, may be put — and 

 with sufficient accuracy, 



= 2ae . 2a sin a> = ^a-e sin w. 

 Hence, we find, by Kepler's first law, 

 A _ 4a^e sin id 

 T ~ ■KuQir-e^)' 

 and consequently, by neglecting the third and higher powers 

 of e, 



_ 4.Te sin a> 



Observing that the eccentricity remains sensibly constant for 

 a period of time, which is doubtless to be reckoned by many 

 tens of thousands of years, we obtain, by means of the formula 

 just found, 



A.Te f"^ /""^ 



1} = ~ — / sin wdw : / dw 



'"' J mi J (01 



_ 4.Te cos eoj - cos a>2 



Finally, by substituting the numerical values of our constants, 

 we shall have the following formulae for computing A and 7) : — 

 A = 465^ sin w, 



_ 465^' ( cos &>! - cos Olj.) 



Wj - «i 



positive values designating that in the Northern Hemisphere and 

 negative values that in ,the Southern Hemisphere the summer 

 exceeds the winter. 



From the first formula we deduce that, for a given eccen- 

 tricity, the disparity in the lengths of the seasons shall be as 

 great as possible when the lineof the equinoxes is perpendicular 

 to the axis major of the orbit. Now, putting e = o, 071, the 

 maximum eccentricity, the values of a and rj for a few values 

 of w are as follows : — 



90 



8501- 95 



80 or 100 



75 or 105 



70 or no 



65 or 115 



60 or 120 



55 or 125 



50 or 130 



45 or 135 



If we remember that the longitude of the perihelion increases 



in about twenty-one thousand years from 0° to 360°, then, it will 



be seen by inspecting these results that, for example, during the 



interval between the two dates corresponding to w = 65° and 



NO. 1209. VOL. 47] 



w = 115°, i.e. during a period of nearly three thousand years, 

 the mean difference between summer and winter will be thirty- 

 two (lays, and that during this period the difference itself will 

 never sink- below thirty days. N. L. W. A. Gravelaar. 



Devenler, Netherlands, December 17. 



Aggressive Mimicry. 



In his last letter Mr. Poulton observes that I am one of 

 "four recent writers " who have made use of the collections in 

 the Natural History Museum and the Museum of the Royal 

 College of Surgeons, for the purpose of iliu-trating the pheno- 

 mena ol mimicry between Volucella and Bomhex. This is the 

 case, but I should like to add that the species which I have 

 depicted are not V. bombylans and B. muscorutn (ihe question- 

 able resemblance of which in nature, and the erroneous labelling 

 of which in the " show ca-es," constitute the grounds of Mr. 

 Bateson's somewhat "aggres-ive" criticism on other " recent 

 writers "), but V. bombylans and B. lapidarius, where the fact 

 of resemblance can admit of no doui.t (''Darwin and After 

 Darwin,'' p. 329). Indeed, Mr. Batesnn fully recognizes the 

 close similarity in appearance between these two species ; and, 

 as Irefrained from giving the hypothetical explanation of it to 

 which he objects, I avoided all the issues which have since been 

 raised in the Nature correspondence. 



Madeira, December 15. George J. Romanes. 



Artificially Incubated Eggs. 

 I have been repeatedly informed by poultry-growers and 

 market-men that hens raised from artificially incubated eggs 

 were much less fertile than those produced in the natural way. 

 My iniormation has been derived from persons who did not 

 even know each other. It occurs to me that if true it is a 

 curious matter and worthy of some attention. 



W. Whitman Bailey. 

 Brown University Herbarium, Providence, R.I. 

 December 10. 



THE PROPOSED UNIVERSITY FOR LONDON. 

 A GENERAL meeting of the Association for Pro- 

 ■^^- moting a Professorial University for London was 

 held on Wednesday, December 21, when a report, 

 which we print below, was presented by the Executive 

 Committee. We would call the attention of our readers 

 to the penultimate paragraph of this report, which indi- 

 cates the existence of an agreement, on matters of prin- 

 ciple between the Senate of the University of London 

 and the Association. 



The last general meeting of members of the Associa- 

 tion was held on June 14, 1892, when the Executive 

 Committee presented for approval a series of proposals 

 for the organization of a University in London. These 

 proposals were adopted as the formal expression of the 

 objects of the Association. 



Since that meeting the efforts of the Committee have 

 been directed to the furtherance of the principles em- 

 bodied in the above-mentioned proposals — by endeavour- 

 ing to obtain the adhesion of literary and scientific men, 

 and of other persons interested ' in the matter ; by 

 organizing a body of evidence to be presented to the 

 Gresham University Commission, and by such other 

 means as have suggested themselves from time to time. 



Immediately after the last general meeting, Prof. 

 Huxley became a member of the Association, and con- 

 sented to accept the office of president. Sir Henry 

 Roscoe and the Master of University College. Oxford, 

 consented to become vice presidents ; and the first of 

 these gentlemen has since been an active member of the 

 Executive Committee. 



The number of members of the Association is now one 

 hundred and fifty. 



Evidence in support of the principles of the Associa- 

 tion has been given before the Gresham University Com- 

 mission by the following gentlemen : — Prof. Ayrton, Mr. 

 F. V. Dickins, Prof. G. C. Foster, Principal Heath, Prof. 



