March 22, 1906] 



NA TURE 



501 



cipal, Mr. J. J. Beringer, in reviewing the growth of the 

 school for the past ten years, made some remarks upon the 

 recent report of the departmental committee on the Royal 

 College of Science. He pointed out that while the fellows 

 of the faculty of mining and metallurgy may be only 

 capable of being produced and fully nourished to maturity 

 in the new institution, yet the general practitioners would 

 still find their way to Camborne for their training. The 

 chairman of the school committee, Mr. C. V. Thomas, 

 remarked that though encouragement was given by the 

 Government and the County Council, sufficient material 

 assistance had always been wanting, and plans for ex- 

 tensions were crippled for want of funds. 



SOCIETIES AND ACADEMIES. 

 London. 

 Royal Society, December 7, 1905. — "A Biomedical Study 

 of Conjugation in Paramaecium." By Dr. Raymond 

 Pearl. Communicated by Prof. Karl Pearson, F.R.S. 



The purpose of this investigation was to determine 

 whether any sensible differentiation exists between the 

 conjugating and non-conjugating members of a population 

 of the common ciliate infusorian Paramaecium caudatum, 

 and to what degree structurally similar individuals tend 

 to pair together in conjugation. The characters principally 

 studied were length and greatest breadth of the body, and 

 the shape of the organism as measured by the length- 

 breadth index. The material used covered a considerable 

 range of cultural conditions. It was found that there is a 

 very considerable differentiation between conjugant and 

 non-conjugant individuals. In respect to the absolute size 

 characters (length and breadth of body), the differences 

 between the means for the two groups of individuals 

 amounted to from 10 per cent, to 20 per cent, of the mean 

 size of the larger (non-conjugant) individuals. Not only are 

 conjugants absolutely smaller than non-conjugants, but 

 they are also sensibly differentiated in shape. Further, 

 they are much less variable, and less highly correlated. 

 There is a strongly marked tendency for like to pair with 

 like in the conjugation of Paramaecium. The coefficients 

 of correlation measuring homogamy in conjugation, are 

 relatively very high, both for direct and cross assortative 

 pairing, in all the characters examined. By an experimental 

 study of random pairings it was shown that this homogamy 

 in conjugation is due to a real assorting and pairing of 

 like with like, and not a spurious effect of local differenti- 

 ation in the culture. Further, by comparing records 

 obtained from recently united pairs of conjugants with 

 similar records from pairs about to separate, it was shown 

 that the results cannot be due to any process of equalisa- 

 tion in size during the process of conjugation itself. The 

 probable manner in which the homogamic pairing is 

 brought about is discussed, and it is shown that the results 

 are easily explicable on the basis of known facts regarding 

 the behaviour of the organism. It is pointed out that the 

 demonstration of the existence of a relatively fixed " con- 

 jugant type " has a direct bearing on current views as to 

 the theoretical significance of protozoan methods of repro- 

 duction. The importance of getting positive evidence that 

 a sensible degree of homogamy actually exists among 

 organisms living under natural conditions has been many 

 times emphasised by writers on evolution. The present 

 work brings forward such evidence for a single organism 

 standing low in the scale of organisation. 



lanuary iS. — " A Case of Regeneration in Polychaste 

 JVorms." Bv Arnold T. Watson. Communicated by 

 Prof. C. S. Sherrington, F.R.S. 



January 25. — " On the Overstraining of Iron by Tension 

 and Compression." By Dr. James Muir. Communicated 

 by Prof. A. Gray, F.R^S. 



The behaviour of mild steel under compression is investi- 

 gated. Compression stress-strain curves are usually shown 

 very much rounded at the yield-point. In this paper a 

 specimen of steel is shown to have obeyed Hooke's law 

 until abrupt permanent shortening occurred at the stress 

 of 21J tons per square inch. At this stress the reading on 

 a Ewing " compression extensometer " altered from 241 to 



NO. 1899, VOL. 73] 



2900 without increase of load. This permanent shortening 

 at the compression yield-point was found to be practically 

 equal to the extension at the tension yield-point of the same 

 material. A second compression test made on the same 

 specimen, after recovery from the compressional overstrain, 

 showed that the compression yield-point had been raised by 

 a step of 4 tons per square inch. This was approximately 

 the step by which the tension yield-point of the material 

 could be raised by tensile overstrain. 



Experiments were further made to investigate the be- 

 haviour under compression of steel which had previously 

 been subjected to tensile overstrain. The experiments seem 

 to indicate that there are two distinct causes contributing 

 to the phenomenon of hardening by tensile overstrain : — 

 (1) the overstraining itself — the actual stretching of the 

 material — seems to harden the material equally as regards 

 both resistance to tension and to compression ; while (2) 

 the process of recovery from tensile overstrain, which seems 

 to bring into existence an internal stress, raises the tension 

 yield-point by a definite step above the overstraining stress, 

 but seems to lower the compression yield-point by approxi- 

 mately an equal amount below the overstraining stress. 

 For example, a specimen subjected to a series of tension 

 tests in which the loading is carried just beyond the yield- 

 point (recovery from overstrain being effected between each 

 test) might exhibit yield-points at 20, 25, 30, 35, and 40 

 tons per square inch. The corresponding compression yield- 

 points should probably occur at about 20, 15, 20, 25, and 

 30 tons per square inch. This conjecture can scarcely be 

 said to have been fully established, further research being 

 necessary ; but it is shown that steel may be hardened by- 

 tensile overstrain to resist higher stresses both in tension 

 and in compression, although material so hardened always 

 withstands a greater stress in tension than in compression. 



February 8. — " Polarisation in Secondary Rdntgen Radi- 

 ation." By Dr. C. G. Bar-kla. Communicated by Prof. 

 J. J. Thomson, F.R.S. 



In a previous paper the author gave an account of ex- 

 periments which demonstrated the partial polarisation of 

 a beam of X-rays proceeding from the anti-kathode of an 

 X-ray focus tube. The secondary radiation from sub- 

 stances of low atomic weight placed in the primary beam, 

 however, varied in intensity in the two principal directions 

 by not more than about 20 per cent. 



The experiments described in this paper were made on 

 the secondary radiation proceeding from a substance of low 

 atomic weight, for, according to the theory given, the 

 radiation proceeding in a direction perpendicular to that of 

 propagation of the primary should be almost completely 

 polarised. 



The method was similar to that used in previous experi- 

 ments, the intensity of tertiary radiation from a light sub- 

 stance placed in the secondary beam being studied by means 

 of electroscopes, shielded from the direct primary and 

 secondary radiations. 



The principal experimental difficulties were due to the 

 weakness of the tertiary beams. 



Carbon was chosen as the radiating substance because 

 the energy of secondary radiation from substances of low 

 atomic weight had been found to be proportional merely 

 to the quantity of matter passed through by a primary of 

 given intensity, and as absorption diminishes with the 

 atomic weight, the lower the atomic weight the greater is 

 the energy of secondary radiation proceeding from thick 

 plates exposed to a given primary. 



A large mass of carbon was placed in the primary beam, 

 and the horizontal secondary beam proceeding from this in 

 a direction perpendicular to that of propagation of the 

 primary was studied. In it was placed a second mass of 

 carbon, and two electroscopes were situated to receive 

 tertiary rays proceeding in horizontal and vertical direc- 

 tions. As the X-ray tube was turned round the axis of the 

 secondary beam, the intensities of tertiary radiation in the 

 two directions changed, one increasing to a maximum while 

 the other decreased to a minimum. 



It was found that the horizontal tertiary reached a maxi- 

 mum and the vertical a minimum when the primary beam 

 was horizontal, and that the conditions were reversed when 

 the primary was turned through a right-angle. 



