158 Scientific Intelligence. 



and ceramics, pigments, etc. The second part treats of Organic 

 industries, connected with the destructive distillation of wood, 

 bones and coal, with mineral oils, with vegetable and animal oils 

 and soaps, with the sugars and fermentation, with explosives, 

 textiles, etc. The volume is well printed and illustrated, g. p. b. 



9. Charge of Electricity carried by the ions produced by 

 Bbntgen Bays.— My. C. T. R. Wilson (Phil. Trans. A., 1897, p. 

 265) has discovered that Rontgen rays can produce a cloudy con- 

 densation in dust-free air when the latter is subjected to a sudden 

 expansion. This condensation cannot be produced by expan- 

 sion without the aid of the rays. Prof. J. J. Thomson has 

 made use of this phenomenon to determine the value of the prod- 

 uct n e v where n is the number of ions in unit volume of the gas, 

 e the charge in an ion, v the mean velocity of the positive and 

 negative ions under a definite electromotive force. The size of the 



drops was determined from the expression v = — - — in which g 



9 /x 



is the acceleration of gravitation ; a, the radius of the drop 



around the ions as nuclei, /x the coefficient of viscosity of the gas 



through which the drops fell. The velocity was determined by 



observing the time the top layer of the cloud took to fall a given 



distance. 



The mean value of the charge on the ion was found to be 



6*5 XlO" 10 . The experiments seemed to show that the charge on 



the ions in hydrogen was the same as in air. From the laws of 



electrolysis, if e is the charge on the hydrogen ion in electrostatic 



units, iV'the number of molecules in 1 cub. centim. at standard 



temperature and pressure, 



JVe= 129 X 10 8 . If eis 



taken as 6*5 x 10 -10 



JV= 20 X 10 18 



When N deduced from experiments on viscosity of air is 



21X10 18 . The agreement between the value of JV got by the 



kinetic theory of gases by viscosity experiments and the value 



obtained by Professor Thomson's experiments, leads him to believe 



that the theory is consistent with the value he has obtained for e, 



being equal to or of the same order, as the charge carried by the 



hydrogen ion in electrolysis. — Phil. Mag., Dec. 1898, pp. 528- 



545. j. t. 



10. Use of the Coherer in Measuring Electric Waves.— It is 

 still a disputed question whether the coherer can be used in the 

 investigation of stationary electric waves. Professor Murani, of 

 Milan, has published an investigation which seems to show that 

 the coherer is too sensitive to such waves, and that having 

 responded to the first electric impulse it is no longer sensitive to 

 succeeding ones. One thus obtains a more or less constant deflec- 

 tion through a galvanometer in the coherer circuit without any 

 evidence of nodes or ventral segments. O. Behrendsen believes 

 that better results can be obtained by using a comparatively in- 

 sensitive coherer, which will only respond to the integrated im- 



