November ii, 1920] 



NATURE 



345 



ill any one term. In teaching biology 1 have constant 

 recourse to the schoril museum. For example, a class 

 may be taken into the museum and a demonstration 

 given of the general characters of the animal king- 

 •!om; or certam exhibits illustrative of one particular 

 ubject can be removed from the cases to the labora- 

 •ry, where, after a short description, they can be 

 cetched by the class. .\ similar use of the museum 

 lor practical education is made by my geological 

 colleague. Further use of the collections has been 

 made for popular demonstrations to members of a 

 local society as well as to parents of boys who visit 

 the school on Speech Day ; on these occasions the 

 boys themselves act as demonstrators. Such, in brief, 

 are some of the uses to which a school museum is 

 put in the service of education. 



That the knowledge of such efforts in education 

 has not come to the powers-that-be only emphasises 

 the deplorable fact of the present lack of co-opera- 

 tion between the school and the universitv. .Xs 

 assistant in the zoological departments of Manchester 

 and St. Andrews Universities 1 learnt the immense 

 v.Tlue of the museum as an aid to biological educa- 

 ^ tion. My experience of school work is confined to 

 the brief period since the close of the war, but I 

 -rtnnot believe that no effort is being made similarlv 

 ■ use the museums of natural history in other 

 liools where a biologist has been added to thi' 

 iff of masters. E. W. Shann. 



Piindjp School. Northamptonihire, 

 October 31. 



Mating Dances of Spiders. 



1 HAVK not, up to the present, found any account 

 : anything approaching to a mating dance, such as 

 IS common among the Salticides, in the Lycosides. 

 The following observations tend to show, I think, 

 that some such dance must exist among certain 

 members of this family. I should be glad to know 

 if any readers of Naturk have met with similar 

 experiences with these spiders. 



The species observed was Lycosa saccata (Black- 



w.iil), which is exceedingly common in the spring. 1 



w IS watching a number of these spiders at about 



p.m. on April 29, 1919. They were sunning them- 



■ Ives on a vertical wooden board leaning against a 



, cucumber frame. I first noticed a male, which was 



about I in. from a female, going through some 



most curious movements. He extended one palp 



•downwards (at about 45°) and the other upwards, at 



: the same sort of angle. He then withdrew them .ind 



I extended them again in the same wav, but with tlicir 



positions reversed. Each time he withdrew them he 



usually took a step towards the female. He repeated 



this two or three times, and then brought the palps 



I to their normal position with a curious quivering 



' movement. The front legs were also caused to quiver, 



\ being hold just off the ground. The front legs of the 



female were occasionalK' seen to quiver also. 



When the male got tip quite close to her (J-J in.) 



Ml.- female ran off, arnl the male searched .'.bout 



thin 2 ft. of where he lost her, exploring crevices, 



.as though looking for her. .\t last he suddenly 



(luntered her round a corner, and she ran nwav. 



• proceeded with his antics, however, without her 



ng there. 



\ new male then appeared and began similar antics 

 front of the female, except that he merely extended 

 h palp separately and returne<l them to tHeir former 

 -ifion. The original male then came up and a fight 

 lied, in which hoth spiders fell off the board, 

 ving the female to continue her basking in (he 

 "■. G. H. I.OCKHT. 



I nrnln College, Oxford, November r. 



NO. 2663, VOL. IO6I 



The Energy of Cyclones. 



I.N X.vruRE of October 28, p. 28(5, Lt.-Col. Gold 

 refers to the theory of the late Dr. Margules, that 

 storms would arise if two masses of air of different 

 temperatures were in juxtaposition. The situation 

 would be unstable, and in passing from this unstable 

 situation to a stable one the potential energy would be 

 reduced, part of it being converted into the kinetic 

 energy of the ensuing "storm." The theory takes it 

 for granted that the warm air rises and the cold air 

 descends. 



But storms are generally associated with cyclonic 

 depressions, and of recent years the temperature dis- 

 tribution in cyclones has been carefully studied. Sir 

 Napier Shaw (Meteorological Office Geophysical 

 Memoir, No. 210b, p. 14) sums up the facts as follows : 

 " The conclusions which we may draw are, first, that 

 the pressure changes at the surface are a reproduction 

 of the pressure changes at the 9-km. level, and that 

 they must be regarded as produced, not by, but in 

 spite of, differences of temperature in the air." 



The theory of Dr. Margules, consequently, fails 

 entirely to account for cyclones. On the other hand, 

 his theory may play some part in the production of 

 line squalls and some thunderstorms. 



With regard to "polar fronts," the theory of Dr. 

 Margules is also :it fault in a great measure. The 

 low-pressure areas over the polar regions produce the 

 two great polar cyclones. The atmospheric columns 

 over the poles must be relatively warmer than those 

 over middle latitudes. .As a result, the warm air is 

 drawn polewards. But, although the atmospheric 

 columns over the polar areas are relatively light, there 

 are cold, dense layers of air resting on the earth's 

 surface. These cold polar layers are pressing out- 

 wards, and where they meet the warm cyclonic in- 

 flows we have the "polar fronts." 



The facts seem to point to the stratosphere as being 

 the main source of energy of storms and trade winds. 



R. M. Df.ki.f.y. 



Tintagil, Kew Gardens Road, Kew, Surrey, 

 October 30. 



Dr. Margules wrote his paper mainly in connection 

 with phenomena of the line-squall type, but he realised 

 that it mighf have wider applications, and later in- 

 vestigations do indicate that discontinuity of tem- 

 perature is the prime factor in the "birlh" of 

 cyclones. If one had an atmosphere with uniform 

 pressure at sea-level, but with masses of warm and 

 cold air, then at 9 km. pressure would necessarily be 

 low in the mass of cold air, and a cyclonic circulation 

 would ensue ; but the energy of the motion would be 

 derived from the potential energy of the initial state. 



Differences of temperature originate in the lower 

 atmosphere. The stratosphere may be able to draw 

 upon a source of energy of which we are ignorant ; 

 it r.innnt of itself provide the energy of storms. 



1:. GOID. 



Luminosity by Attrition. 



]s reference to the letter in NATfRK of November 4, 

 p. 310, by Sir E. Ray I^nkester on the above pheno- 

 menon, it may be of interest lo some to know that 

 Thomas Wedgwood was the first to direct attention 

 to the fact that light could be pnxluced by the rubbing 

 together of Quarl/ or sugar. His paper on "Experi- 

 ments and Observations on the Production of Light 

 from Different Bodies by Heat and Attrition " may 

 lie found in Phil. Tr.in<. Roy. Soc, 1792, part i. 



C. Caris-Wilsos. 



Voyembrr 6. 



