APRIL 7, 1923] 
itive factor. This latter appears to be affected 
Fpatthatc conditions, since American cottons grown 
in India show, on the addition of food material, an 
accelerated rate of deterioration. Selective breeding 
might possibly assist in the isolation of strains of 
cotton resistant to bacterial attack.—E. Hatschek : 
The standard methods of ultra-microscopy. The 
methods of making visible those particles small 
compared with the wave-length of light (roo uu and 
less) fall into two classes: (1) illumination at right 
angles to the axis of the microscope (Zsigmondy- 
Siedentopff ultra-microscope and Jentzsch ultra- 
condenser), and (2) axial illumination so arranged 
that direct light is totally reflected at the cover 
glass (dark ground condensers, e.g. paraboloid, 
cardioid, concentric, etc.). The performance of the 
slit ultra-microscope was discussed. 







Royal Meteorological Society, March 21.—-Dr. C. 
Chree, president, in the chair.—G. M. B. Dobson: 
Characteristics of the atmosphere up to 200 km., as 
obtained from observations of meteors. The rate of 
heating and evaporation of a meteor depends on the 
air density. Nearly all the kinetic energy of the 
meteor is finally radiated as visible light, and thus 
observations of a meteor’s total brightness and 
‘velocity give its mass. Hence from the observed 
characteristics of meteors it is possible to calculate 
the density of the air at the height of their appearance 
and disappearance. The rate of change of density 
with height will indicate the air temperature. From 
eye observations of meteors the temperature of the 
air is about 220° a. (-63° F.) up to 50 km., thus 
agreeing with the results of ballon sondes. Above 
60 km. the temperature is about 300° a. (81° F.), and 
the density at 100 km. is about 100 times greater 
than that usually calculated on the assumption of a 
uniform temperature of 220° a. The high tempera- 
ture is presumably due to the absorption of solar 
radiation by the air in addition to terrestrial and 
atmospheric radiation, due possibly to the presence 
of ozone formed at great heights by the sun’s ultra- 
violet light. There is indirect evidence of an annual 
variation of air temperature. 
DuBLIN. 
Royal Dublin Society, February 27.—Prof. J. A. 
Scott in the chair—P. A. Murphy: On the cause of 
rolling in potato foliage ; and on some further insect 
carriers of the leaf-roll disease. The mechanism of 
rolling of potato foliage as caused by leaf-roll, and 
incidentally by some other diseases and injuries, is 
_ discussed. The cause of rolling in the cases investi- 
3 em dis the distension of the spongy parenchyma 
ollowing the accumulation of carbohydrate in the 
leaves. The activities of a capsid (Calocoris bipunc- 
tatus), a jassid (Typhlocyba ulmi), and an aphis 
_(Myzus Persice) which develops on the sprouts of 
unplanted tubers, in carrying leaf-roll are discussed. 
—John J. Dowling: The recording ultramicrometer : 
its theory and applications. The theoretical prin- 
ciples of the device, together with a description of 
some experimental investigations into the conditions 
of operation, are discussed. The degree of sensitivi 
attained under ordinary laboratory conditions is 
to-? cm.; this being strictly reproducible and the 
apparatus quite easy to operate. The operation of 
e ew at still higher sensitivities requires 
special precautions, such as screening and the like. 
March 27.—-Prof. J. A. Scott in the chair.—R. L. 
Praeger : Catalogue of scientific and technical period- 
-icals in Dublin libraries. A card-index catalogue 
_ showing all the scientific periodicals available in Dublin 
_ has been prepared by a special committee. In each 
NO. 2788, VOL. 111] 
NATURE 
_and the availability of iron. 
487 
case the extent of the sets in each library is shown, 
together wit any breaks which occur. Thus it is 
possible to ascertain if any number of any periodical, 
whether current or extinct, is available in Dublin, 
and where it is to be found. It is proposed to 
endeavour to improve the supply of such literature 
by suggesting the discontinuance of some periodicals 
which are unnecessarily reduplicated and their replace- 
ment by others at present unavailable—-W. R. G. 
Atkins: The hydrogen ion concentration of the soil in 
relation to the flower colour of Hydrangea hortensis W., 
The hydrangea produces 
blue flowers when grown in acid soil, since iron salts are 
absorbed in larger amou.its and react with the pink 
flower pigment. Iron is absorbed by plants mainly 
in the ferrous condition, for at ordinary soil P, values 
ferric iron is completely precipitated. Ferrous salts 
are not completely precipitated at Px7. The lessened 
solubility in alkaline soils is considered in relation to 
chlorosis. Iron pan formation is connected with the 
oxidation of the ferrous hydroxide precipitated when 
acid soil solution percolates to a region of higher Px 
value.—H. G. Becker and E. F. Pearson: Irregular- 
ities in the rate of solution of oxygen by water. A 
form of apparatus is described which permits the 
process of absorption to be observed continuously by 
means of a sensitive water manometer, the tempera- 

‘ture being maintained constant to o-1° C, The 
results obtained show that during the early stages, 
absorption follows a logarithmic curve very closely, 
but after the gas-content has risen to about 70 per 
cent. of saturation the absorption tends to become 
irregular. This indicates that the force producing 
the slow mixing during the early stages tends to 
become very small, and therefore uncertain in its 
action towards saturation. 
Paris. 
Academy of Sciences, March 12.—M., Albin Haller 
in the chair.—Luigi Bianchi: A kinematic property 
of W surfaces.—M. Jules Bordet was elected a foreign 
associate in succession to the late M. Ciamician, and 
M. J. Cornet corresponding member of the section of 
mineralogy in succession to M. W. C. Brégger, elected 
foreign associate. — Mordoukhay-Boltovskoy: The 
logarithm of an algebraic number.—M. Hadamard : 
Remarks on the preceding communication.—M. 
Mandelbrojt : Taylor’s series with gaps.—M. Malaval : 
Hardening (of metals). Metals can be hardened not 
only by longitudinal extension (Seigle) but also by 
compression, and the latter method was applied in 
1912 to a gun, with good results.—Georges Darmois : 
The local integration of Einstein’s equations (interior 
problem).—M. Cisotti: Plane movements of liquids 
endowed with viscosity—D. Eginitis: The reform of 
the calendar in Greece. A discussion of the political 
and ecclesiastical difficulties attending the reform of 
the calendar in Greece.—M. de Broglie and E. Friedel : 
The diffraction of the X-rays by smectic bodies. 
The smectic state is defined. as one in which the 
molecules, having a common direction, are distri- 
buted along parallel equidistant surfaces. Such 
substances should act on X-rays like the system of 
parallel reticular planes of a crystal. In_confirma- 
tion of these views experiments on the diffraction of 
X-rays by solutions of sodium oleate are described. 
Combined with the experimental figures of P. V. 
Wells, these results form the first direct measurement 
of the wave length of the X-rays starting with optical 
wave lengths, and without making use of either 
Avogadro’s constant or Planck's constant.—J. 
Cabrera: The limits of K absorption of some ele- 
ments. Results are given for a group of sixteen ~ 
elements, mainly from the rare earths.—M. Volmar : 
