830 



NA rURE 



[June 24, 1922 



Societies and Academies. 



London. 



Royal Society, June i. — Sir Charles Sherrington, 

 president, in the chair. — T. H. Morgan : The mechan- 

 ism of heredity (Croonian lecture). The changes 

 taking place when the germ-cells ripen are such that, 

 granting the hereditary elements are carried by the 

 chromosomes, the changes can serve as a mechanism, 

 furnishing an explanation of the principles of heredity 

 discovered by Mendel. In the course of the ripening 

 of the germ-cells, irregularities occur at times in the 

 distribution of the chromosomes, which can be followed 

 in successive generations. The departures from the 

 ordinary course of inheritance that are there shown, 

 are found to be exactly related to the new distributions 

 of the chromosomes. The facts furnish convincing 

 testimony that the Mendelian characters are carried 

 by the chromosomes. By the aid of the phenomenon 

 known as " crossing-over " it is possible to determine 

 that the hereditary elements lie in a single line in 

 each chromosome. It is even possible to form a rough 

 estimate of the upper limits of size of these elements, 

 although at present such estimates are necessarily 

 very crude, and are interesting only as the first 

 attempt to determine the size of the " gene." 



Geological Society, May 24. — Prof. A. C. Seward, 

 president, in the chair. — A. C. Seward : Geological notes 

 on western Greenland. Many localities were visited on 

 the northern and north-eastern coasts of Disco Island, 

 on the coast of Nugsuak Peninsula, also Hare Island, 

 Upernivik Island, Ritenbenk, Sarkak, and Jakobs- 

 havn. Greenland is nearly 1700 miles long, with an 

 average breadth of about 600 miles ; approximately a 

 hundred glaciers from the inland ice reach the sea, 

 the largest of which, Humboldt Glacier, ends in a 

 cliff 60 miles broad. Various forms of icebergs were 

 seen. An account of the characteristic types of 

 vegetation and the physical and geological features 

 of Greenland was followed by a more detailed descrip- 

 tion of the Cretaceous and Tertiary sedimentary 

 series of Disco Island and the Nugsuak Peninsula, 

 and of the overlying and protecting basalts which in 

 some places rest directly upon the old Archaean 

 land-surface, to the exclusion of the sedimentary 

 series. Most of the sedimentary rocks are freshwater 

 in origin and there is evidence of recent sinking of 

 parts of the western coast. 



Linnean Society, June i. — Dr. A. Smith Woodward, 

 president, in the chair. — A. C. Seward : A study in 

 contrasts : The past and present distribution of 

 certain ferns (Hooker lecture). Ferns spread by 

 vegetative means, and the hghtness and resistant 

 nature of their spores make them very successful 

 as colonisers and emigrants. When Treub visited 

 Krakatau three years after its violent volcanic 

 eruption, he found eleven species of ferns as pioneers 

 of the new flora. As a class, ferns are cosmopolitan, 

 though certain of them are strictly limited in their 

 range and highly sensitive to the influence of physical 

 or cUmatic conditions, e.g. the Bracken, Cystopteris 

 fragilis, and Polystichum Lonchitis. The apparent 

 identity of living with dead plants gives reality to 

 Hooker's idea expressed in one of his letters : 

 " Geology gives no evidence of a progression in plants. 

 I do not say that this is a proof of there never having 

 been a progression — that is quite a different matter — 

 but the fact that there is less structural difference 

 between the recognisable representatives of Conifers, 

 Cycadeae, Lycopodiaceae, etc., and Dicotyledons of the 

 chalk and those of the present day, than between the 

 animals of those periods and their living representa- 



NO. 2747, VOL. 109] 



fives, appears to me a very remarkable fact." The 

 unfolding of plant-Ufe through successive stages of 

 earth-history shows a series of outbursts of energy ; 

 the records of one period tell us nothing, while those 

 of the next reveal a fresh type of vegetation or, it 

 may be, a single genus in possession of widely 

 scattered regions of the world. The beginnings are 

 always hidden from us. Between the Mesozoic 

 and the Palaeozoic records there appears to be a wide 

 gulf. The difficulty of making direct contact between 

 the age of pteridosperms and the succeeding age of 

 ferns may be due to the difficulty of determining 

 whether a Palaeozoic fern-like frond should be classed 

 as a pteridosperm or a true fern. In the latter part 

 of the Triassic period we seem to pass suddenly 

 to a new phase of plant evolution which may be 

 intimately associated with some far-reaching event 

 in the physical history of the earth's crust. Possibly 

 crustal foldings in the latter part of the Palaeozoic 

 era, and the prevalence of desert or semi-arid con- 

 ditions over wide regions during a part of the Triassic 

 period, were vital factors influencing the progress 

 of plant development. The rocjfs accessible cannot 

 give all the clues sought ; parts of old continents 

 remain but others are beyond our reach. 



The Optical Society, June 8. — Sir Frank Dyson, 

 president, in the chair. — J. Guild : Angle comparators 

 of high precision for the goniometry of prisms. The 

 method of substitution is utilised. Measurements 

 accurate to i"-2" can readily be made, and with a more 

 elaborate arrangement an accuracy of about o-i" is 

 possible. For the latter, minute variations in the direc- 

 tion of a beam of light emerging from a coUimator, 

 caused by placing near the focal plane of the latter 

 a " variable prism " of simple design, are measured. — 

 T. Smith : The changes in aberrations when the object 

 and stop are moved. If the aberrations of any centred 

 optical system are known, both for an object which 

 intersects all rays transmitted by the system and 

 for the centre of the effective stop, the position in 

 the image space of the emergent portion of a given 

 incident ray is known, and the aberrations in the 

 image of any other object for any stop position can 

 be expressed in terms of those for the first object. 

 The relations in the second case are expressed in 

 terms of the first when the objects are planes normal 

 to the axis of symmetry. — T. Smith : The classifica- 

 tion of optical instruments. Five classes are proposed, 

 based upon the separation of the four Gaussian con- 

 stants into two groups according to their signs. 

 This classification cannot be modified by the addition 

 to the system of inverting prisms and the like, and 

 the properties usually associated with the sign of the 

 lens depend upon its class according to the new system. 

 Each class may have systems of positive or of negative 

 power. — T. Smith and L. M. Gillman : Note on 

 achromatism with one glass. Systems composed 

 of thin lenses of the same kind of glass, and 

 achromatised by selecting suitable positions for the 

 components, are members of the class (AD) (BC), so 

 that if the object is real the image is virtual. Apo- 

 chromatic systems constructed from normal achro- 

 matic lenses belong to the same class. The aberra- 

 tions for systems constructed of a single glass, but 

 belonging to other classes, are of considerable 

 magnitude. — H. S. Ryland : An improved subjective 

 test for astigmatism. The test apparatus consists 

 of an opaque disc perforated along two diameters 

 at right angles with a series of square apertures. 

 These apertures and the distances between them 

 subtend angles of i' at the usual testing distance. 

 The plate is illuminated by diffused light from the 



