Magnesium carbonate, or 'chalk', is used by rock climbers to dry their hands to increase the coefficient of friction, thereby improving the grip of the holds. To date, no scientific research supports this practice; indeed, some evidence suggests that magnesium carbonate could decrease the coefficient of friction. Fifteen participants were asked to apply a force with the tip of their fingers to hold a flattened rock (normal force), while a tangential force pulled the rock away. The coefficient of friction--that is, the ratio between the tangential force (pulling the rock) and the normal force (applied by the participants)--was calculated. Coating (chalk vs no chalk), dampness (water vs no water) and rock (sandstone, granite and slate) were manipulated. The results showed that chalk decreased the coefficient of friction. Sandstone was found to be less slippery than granite and slate. Finally, water had no significant effect on the coefficient of friction. The counter-intuitive effect of chalk appears to be caused by two independent factors. First, magnesium carbonate dries the skin, decreasing its compliance and hence reducing the coefficient of friction. Secondly, magnesium carbonate creates a slippery granular layer. We conclude that, to improve the coefficient of friction in rock climbing, an effort should be made to remove all particles of chalk; alternative methods for drying the fingers are preferable.

More than 50 very large BF3 counters, each approximately 6 ft (180 cm) long and 6 in. (15 cm) in diameter have been made for cosmic-ray monitors. During the fabrication of these counters, the characteristics at varying gas pressures have been studied and the alpha backgrounds of the various metals used for cathodes have been determined. The counters have excellent characteristics at pressures up to 30 cm Hg and perfectly acceptable characteristics to 60 cm Hg pressure. With anode diameter 0.008 in. (0.2 mm) and gas amplification 35, the operating voltage for a filling of 20 cm Hg pressure of pure BF3 is 2800 V; at 30 cm Hg it is 3400 V. Counters with copper cathodes have backgrounds due to residual alpha contamination of about 2 counts/min, and with stainless steel cathodes, about 5 counts/min. Using a BF3–Ar filling a value of 6.30±0.05% has been obtained for the branching ratio of the B10(n,α)Li7 reaction.

Boron trifluoride proportional counters of calculable efficiency for neutron beam measurements are described. It has been found possible to obtain excellent pulse-size distributions with a filling of 60 cm of purified BF3 by ``soaking'' the counters for a long time (up to three months) with BF3 before putting in the final filling. These fillings are stable. Fillings of less than 5 cm BF3 made up to 50 cm with argon have also been studied. With these fillings the pulse-size distributions are very good for both beam and total irradiation conditions. A discussion of the counter efficiencies with particular reference to end correction is given.

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2014 On décrit la croissance de cristaux de tellurure de cadmium en solvant tellure et par la méthode « THM ». La densité des inclusions de tellure dans les cristaux a été étudiée ; on a pu montrer que dans une certaine gamme de vitesses de croissance et de gradients de température, il est possible d'obtenir des cristaux dépourvus d'inclusions de tellure.Abstract. 2014 CdTe crystals have been grown from a slowly cooled Te solution and with the travelling solvent method. The density of visible Te inclusions in the crystals has been investigated and it was found that inclusion-free material can be grown if the growing speed and the temperature gradient in the melt are kept within certain limits.