Geology and Mineralogy. 509 



included in this division. Class 4. Bodies analogous to water 

 which include no ions or very few which permit movement. 

 These can be called hydrides.— Ann. der Physik und Chemie, 

 No. 11, 1894, pp. 401-431. j. t. 



11. Electrical conductivity of absolutely pure vmter. — Kohl- 

 rausch and Hetdeweiler describe the processes by which they 

 prepared and tested samples of pure water. They endeavored to 

 find the true conductivity of water by extrapolation from previ- 

 ous experiments. The value thus obtained for the conductivity 

 of absolutely pure water at 18° C. is 0*036 X10~ 10 . The amount 

 of residual impurity was estimated at a few thousandths of a 

 milligram per liter, which is 10,000 times less than the amount 

 of air normally absorbed from the atmosphere. — Ann. der Physik 

 und Chemie, No. 10, 1894, pp. 209-235. j. t. 



12. Self induction and capacity of coils. — C. Fromme from 

 magnetic experiments shows that bifilar wound coils possess a 

 small capacity, so long as their resistance does not exceed 1000 

 ohms. At 2000 ohms the capacity begins to reach an appreciable 

 amount. Chaperon's coils, however, so far as they were tested 

 up to 3000 ohms were found free from capacity and self induc- 

 tion. These coils are unifilar. The direction of the winding 

 changes with each layer. — Ann. der Physik und Chemie, No. 10, 

 1894, pp. 236-266. J. T. 



13. /Spirals with compensated self induction. — The difference of 

 potential between neighboring turns in an ordinary coil is in gen- 

 eral small, so that the capacity is small and is only noticeable 

 with currents of high frequency. In order to obviate this capac- 

 ity, Tesla recommends winding a wire B parallel to the first 

 wire A and connecting the end of A with the beginning of B. — 

 Lum. Electr., li, pp. 432-433, 1894. j. t. 



II. Geology and Mineralogy. 



A pre- Olenellus fauna : "On the Cambrian Formation of 

 [he Eastern Salt Range." By Dr. Fritz Noetung, F.G.S. Records 

 of the Geological Survey of India, Vol. xxvii, part 3, pp. 71-86, 

 August, 1894. — From researches made in the palaeozoic rocks of 

 the Salt Range of India by the Geological Survey of that country, 

 Dr. R. D. Oldham points out* what are the accepted divisions of 

 the Cambrian rocks of that region and gives numerous lists of the 

 fossil remains recognised up to date. In these lists such genera 

 as Olenellus, Tlyolithes, Conocephalites and Neobolus are re- 

 corded. There was however considerable confusion and mixture 

 of horizons in the succession as known. Dr. Noetling has gone 

 carefully into the natural succession of the Cambrian and newer 

 palaeozoic strata of the Eastern Salt Range. He separates the 

 upper and middle portion of the Palaeozoic from the lower and 

 Cambrian portion. 



* Manual of the Geology of India, Chapter V, p. 113 et seq., Calcutta, 1893. 



