4/2 



NATURE 



[June i» 191 



the significance of mimetic resemblances. At Prof. 

 PouUon's request the author undertook in the summers of 

 1909 and u)io to make a series of experiments in the 

 (gardens of the society to test the edibility of various British 

 insects, most of which were sent to him, together with 

 some slugs, by Dr. («. B. Ix>n{'stafT. The insects com- 

 prised Lepidoptera, Coleoptera, Orthoptera, llemiptera, 

 Diptera, and Ilymenoptera, and the most interesting of 

 the experiments were those made with the bumble-bee 

 (Bombus) and its mimetic fly (lo/ucW/a bowbylans) to 

 test the theory of mimicry. The I?<imbus proved to be 

 unpalatable to nearly all birds. The birds would try them 

 a varying number of times. When they had learnt their 

 distastefulness by experience, they refused to touch them, 

 and then when offered the V'olucella refused that likewise. 

 A considerable number of species of insectivorous birds 

 were tested in this way, and always with the same result ; 

 and the one specimen of Volucella hombylans that did duty 

 for some thirty or forty experiments went through the 

 ordeal untouched. — Prof. G. C. Bourne, F.R.S. : The 

 second portion of his paper on the morphology of the group 

 Neritoidea of the aspidobranch gastropods, which dealt 

 with the Helicinid.TC. The author stated that this family 

 was capable, by some unknown means, of wide dispersal 

 across seas and oceans, and that the conditions most suit- 

 able to its existence were found in proximity to the sea. 

 In describing the anatomy, the genus .Mcadia was taken 

 as the type, and the differences between it and the other 

 genera were pointed out, but the species, and even the 

 genera, of Helicinidae were closely similar, anatomically, 

 from wliatever part of the world they came^ — J. J. 

 Lister, F.R.S. : The distribution in the Pacific of the 

 avian family Megapodidn:. 



Mathematical Society, May ii. — Dr. H. F. Baker, 

 F.R.S., president, in the chair. — G. T. Bennett: The 

 kinematical and geometrical theory of a deformable octa- 

 hedron. — J. W. Nicholson : The scattering of light by a 

 large conducting sphere (second paper). 



Physical Society, May 12. — Prof. H. L. Callendar, 

 F.R.S., president, in the chair. — Sir G. Greenhiil and 

 Colonel R. L. Hippisley : Diagrams of stream lines past 

 an elliptic cylinder. — J. T. Morris and T. H. Lang^ford : 

 The method of constant rate of change of tlu.\ as a 

 standard for determining magnetisation curves of iron. 

 The research described was instituted with the object of 

 finding what differences there were between the magnetisa- 

 tion curves for a given sample of iron when determined 

 (i) by the older methods in which the flux is changed 

 suddenly, (2) by a method in which it is changed exceed- 

 ingly slowly and at a uniform rate. The methods experi- 

 mentally examined were : — (i) method of constant rate of 

 change of flux ; (2) " slow cyclic " hysteresis loops by 

 method (i) ; (3) " step by step " magnetisation curve ; 

 (4) " step by step " hysteresis loops ; (5) method of 

 reversals " ; (6^ alternating-current magnetisation curve. 

 Details are given of the theory and practical working of 

 method (i). In this method the magnetising current is 

 continuously increased through a primary winding by a 

 specially designed resistance at such a varying rate as to 

 maintain a constant voltage generated in a secondary 

 winding. A certain amount of skill is required in 

 operating the resistance, but an average experimenter may 

 easily acquire this with a little practice. The complete 

 change of the current occupied times varying from one up 

 to some five minutes. Tables are given of the magnetisa- 

 tion curve deteritiined by the six different methods at a 

 number of values from H 03 up to 700, and of the 

 permeability from B 500 up to 17,000. At low values of 

 the magnetising force the uniformly varying flux method 

 gives results of some 200 lines per square centimetre in 

 excess of the older methods. .-\s regards the time required 

 for determinations by the various methods experimentally 

 examined, ballistic methods are undoubtedly the most 

 tedious. The alternating-current method (method 6) has 

 considerable advantages in this respect, a full set of read- 

 ings of magnetising current and induced voltage occupy- 

 ing a verv short time. When, however, it is necessary to 

 take oscillograms at various points in order to plot curves 

 of form factors, the time required is enormously incre.-'sed. 

 The method of uniformly vri'ving flux (method 1) is 



NO. 2170, VOL. 86] 





peculiarly adapted for use where time in a consideratii 

 and at the same time a high degree of accuracy is desin 

 A complete magnetisation curve may be taken in a v< 

 few minutes, and the mean of many such curves obtaii 

 in, say, one hour, the iron being dema,' ' ' 



each test. The method of *' uniform!- 



appears to possess advantages, both si i' : 



tical, over the older methods in use for the testing <it ringt] 

 samples of magnetic materials. It avoids diflliculties due/ 

 to eddy currents and magnetic viscosity, which eflfects ai 

 themselves due primarily to rapid or irregular chang(>« 

 flux. Besides rapidity of experiment, it also 1 

 advantage of accuracy of repetition under standard 

 determined conditions of magnetic change. The 

 is, therefore, commended for the carrying out of n 

 tests, especially where great accuracy under d 

 known conditions of experiment are essential. 



Royal Anthropological Institute, May 23. — Dr .\ < 

 Haddon in the chair. — S. H. Warron : The classification 

 of the prehistoric remains of east Essex. The district of 

 eastern Kssex is formed of a plateau deeply trenched by 

 river valleys. On the plateau, and also at lower levels, 

 are numerous Pala;olithic deposits. The paper d ■ ' '- 

 detail with the later prehistoric remains only. T: 

 valleys were cut at a time when the land stood 

 relatively to the sea, than it stands to-day. .\s - 

 gence set in, the lower reaches of the valleys were 

 by the sea, and they became partially silted up with lidal 

 clay. Upon the former dry land surface, now buried 

 beneath the tidal clay, large numbers of prehistoric remains 

 have been found. These include polished axe-heads, knives, 

 arrow-points, and other flint implements. .\mong the 

 pottery, some remains of the *' drinking-cup," or 

 ■' beaker," have been found, and it is to this archaeo- 

 logical stage that this buried prehistoric surface is referred. 

 Beneath this surface, deposits of rain-wash are found 

 which yield an earlier series of prehistoric remains. Thesf 

 are post-Pahcolithic, as they include polished stone ax- - 

 barbed arrow-points, and pottery. The question of tl 

 position which these remains should occupy in the pr 

 historic succession was discussed. The advantage of usiv^ 

 a sequence date scale, rather than a succession of epot 

 with indefinite and overlapping boundaries, was insist. ! 

 upon. — Dr. A. Keith : A prehistoric skeleton. The skele- 

 ton, described in an appendix to the foregoing ppper. 

 belonged to the horizon of the buried surface. It wa- 

 remarkably perfect, and was that of a woman of abou' 

 ti\^enty-five to thirty years of age. .Although of small 

 cranial capacity, it was of fairly high type. The skull 

 inclined to the round-headed form, the index being 77->'- 

 The stature, 5 f< ' t 4 inches, or slightly less, the limb 

 bones slender, thi haiitis and feet small. It was buried in 

 the contracted position. The body had been swathed in 

 the tough roots of the sand-grass, while within the cavity 

 of the body a considerable quantity of the seeds of the 

 blackberry and the dog-rose was found. These were un- 

 doubtedly the remains of food. 



Cambridge. 

 Philosophical Societv, May 8. — Prof. Seward, F.R.S.. 

 vice-president, in the chair. — H. Hamshaw Thomas : The 

 spores of some Jurassic ferns. A preliminary note record- 

 ing the discovery in the estuarine shales of the York- 

 shire coast of the spores and sporangia of Coniopteris 

 hymenophylloides (Brongn) and Todites n'illiamsoni 

 (Brongn). In the case of the former species, further 

 evidence is afforded for the inclusion of this Jurassic type 

 in the Cyatheaceae, while the spores of Todites are shown 

 to be almost identical with those of the recent Todea 

 barbara. — C. E. Moss : A new species of Salicornia from S 

 Angola. The specimens on which this communication is | 

 based were collected by Welwitsch during his travels in ^ 

 .Angola between 1853 and 1S61, and are preserved in the J 

 British Museum (Natural History). By Mr. Hiern < 

 (" Catalogue of .African Plants collected by Dr. Friedrich 

 Welwitsch," iv., 1900, pp. 800—900), the plant is referred ^^ 

 to Arthrocnemum macrostachyum ( = Salicornia glauca). 

 Welwitsch himself regarded it as a species new to science, 

 wrote out a full description of it in Latin, and provision- 

 ally named it (in MSS.) Arthrocnemufn angolense. There 

 can be no doubt that Welwitsch 's surmise was cof-r* -.s 



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