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IN examining the problem of survival of men immersed in cold Arctic waters, it is clear that the rate of cooling of the body will be of signal importance, and Glaser1 has recently directed attention to the fact that heat losses from the human body immersed in cold water can be balanced, and the temperature of the deep tissues maintained, by exercise. In addition, however, survival may well depend very significantly on the maintenance of some degree of manual dexterity for clambering on to rafts, wreckage, etc.

At a given temperature, the heats of immersion of ‘Graphon’ in individual members of a series of n-alkanes (hexane to hexadecane) show a remarkable increase with increasing chain length. This effect, first noted by Robert1, has since been independently confirmed by Everett2 and also in our own laboratories. We have also found that the heat of immersion of ‘Graphon’ in n-alkanes of longer chain length is very dependent on temperature.

PRESENT research on plant–water relationships emphasizes the need to evaluate the water balance in the plant.

It is not uncommonly supposed that if light falls on a dense-rare interface at more than the critical angle, no energy can penetrate into the rarer medium. Several workers1 have shown that a certain amount of energy can penetrate a short distance, but that the disturbance is much attenuated and becomes negligible at a few wave-lengths distance from the interface. This is in accordance with Huyghens' construction2 (see diagram, full circles), which gives in this case a series of secondary wavelets lying wholly within their neighbours, and hence not cutting and reinforcing at any considerable distance.

WHEN a well-corrected oil-immersion objective is used to examine dust particles mounted in a medium such as Canada balsam, of similar refractive index to the oil, the finer particles will give a very similar image on either side of the correct focus, provided the objective is used at the tube-length for which it is designed. We have found, however, that if the dust deposit is mounted dry on the underside of the microscope cover-glass, the image on either side of the correct focus is not the same at the specified tube-length, and in order to obtain the best images, the tube-length must be reduced.

IN NATURE, vol. xxi. p. 602, I have read an interesting account of Prof. Hughes's experiments on the change produced in iron and steel wire by immersion in acidulated water.

IN daily observations on the structure of chromosomes fixed and stained in iron-acetocarmine (see American Naturalist, 1921, pp. 573–574), where the limit of resolution in the microscope must be maintained, it has been determined that water is, on the whole, to be preferred to cedar oil as an immersion fluid for the condenser. The corrections necessary are readily made, (I) By centring a large enough meniscus lens from a photographic camera below the condenser (Hartridge); and varying the distance of the light source, and the thickness of the object slide, until the best image of a grating close to the light source is obtained. (2) By unscrewing sufficiently the top lens or lenses of the condenser. Slides can easily be selected of approximately the required thickness. The test for aplanatism is, of course, to diaphragm the source of light until its image is equal to or smaller than the field of view, and then observe the light circle at the back of the objective.

THE phenomenon described by Messrs. Beadle and Patterson in NATURE of August 19, p. 327, is well known to practical microscopists, since it occurs whenever a considerable change in the working aperture of a wide-angled objective is made, and admits of a simple explanation.

‘THOROTRAST’ (colloidal thorium dioxide) can be identified quite easily in tissue sections when using an ordinary light microscope, provided that it is present in sufficient quantity. Under such conditions ‘Thorotrast’ is seen as characteristic refringent brownish clumps.

AT the London Optical Conference in 1950, it was suggested1 that the resolving power R of diffraction gratings might be increased by immersing the grating in a medium of high refracting index μi. Thus: where W is the ruled width of the grating and where α applies for the case of autocollimation of incidence and diffraction. This idea, which is a strict parallel to that of the immersion microscope, was further developed2 in accordance with Figs. la and b.

Voyager 2 approaches Saturn (♄ ) this month, August 1981, after the possible encounter1,2 of the planet with the tail or wake3 of Jupiter (♃). With the magnetic flux in the tail of φ≅2 × 1012 Wb (refs 4,5) a simple model suggests that the tail is very long (7–15 AU) and wide enough (∼0.6 AU) to engulf Saturn. This could result in a sudden drop (by a factor of ∼40) of the ram pressure on the magnetosphere of Saturn. The ensuing inflation of the magnetosphere may cause effects observable from Voyager 2 and/or Earth-orbiting satellites, including a flare-up of kilometric radiation and enhancement of the Lyα limb brightening. Such events, if observed, could shed light on the magnetic and plasma nature of the jovian tail and on the electrodynamics of the saturnian magnetosphere.

IN some experiments reported recently by Moreau and Chaudron1, it was found that prolonged immersion of high-purity aluminium in dilute (N/100) caustic soda solution resulted in the absorption of large quantities of hydrogen by the metal, and that the presence of this gas had a measurable effect upon the elastic modulus. After 20– 30 days immersion, the hydrogen content, measured by an ion-bombardment extraction method, was found to be as high as 1,000 c.c. per 100 gm. of metal. This measurement was carried out on specimens turned down from the original corroded blocks, and the results would, therefore, indicate that the absorbed hydrogen had penetrated to a considerable depth in the metal.

IT is well known that if collagen is heated in water to about 62° C. it undergoes shrinkage, and that if it is then allowed to dry, its ability to re-hydrate on immersion in water is considerably reduced. Although opinions differ as to the precise mechanism of hydrothermal shrinkage, the phenomenon is generally agreed to be a cumulative effect in which the polypeptide chains, by the rupture of certain cross-links of various strengths, assume a more compact space arrangement than their hitherto extended forms. On drying in this compact state, their ability to take up water is considerably reduced, due probably to the formation of fresh inter-chain links.

International audience; Although the local resistivity of semiconducting silicon in its standard crystalline form can be changed by many orders of magnitude by doping with elements, superconductivity has so far never been achieved. Hybrid devices combining silicon's semiconducting properties and superconductivity have therefore remained largely underdeveloped. Here we report that superconductivity can be induced when boron is locally introduced into silicon at concentrations above its equilibrium solubility. For sufficiently high boron doping (typically 100 p.p.m.) silicon becomes metallic(1). We find that at a higher boron concentration of several per cent, achieved by gas immersion laser doping, silicon becomes superconducting. Electrical resistivity and magnetic susceptibility measurements show that boron-doped silicon (Si:B) made in this way is a superconductor below a transition temperature T-c approximate to 0.35 K, with a critical field of about 0.4 T. Ab initio calculations, corroborated by Raman measurements, strongly suggest that doping is substitutional. The calculated electron-phonon coupling strength is found to be consistent with a conventional phonon-mediated coupling mechanism(2). Our findings will facilitate the fabrication of new silicon-based superconducting nano-structures and mesoscopic devices with high-quality interfaces.

This week Daedalus describes his plans to create 'Liquid Air' — a dense breathable foam, containing salts that bring it into osmotic balance with lung tissue, which contains 74% of air by volume. His planned applications for the foam include a relaxing immersion bath and, because of its high water content, uses in firefighting.