Intelligence and Miscellaneous Articles. 1 33 



The general succession of the greatly disturbed Portraiue Lime- 

 stone Series from above downwards is : — '3. Thin-bedded limestone, 

 with shaly partings ; 2. Beds of compact crystalline limestone, 

 with many fossils ; 1. Thin-bedded limestones, with shaly partings : 

 the upper beds being in places crowded with corals. This limestone 

 is comparable with the Chair of Kildare Limestone, and also with the 

 Sta wocephalus, Keisley, and Sholesbrook Limestones of Great Britain. 

 Succeeding the Limestone Series, and separated from it by a thrust- 

 conglomerate, is a Grit Series, which has yielded no fossils, but 

 which resembles the Balbriggan Grits containing black shales with 

 Birkhill graptolites. 



Mr. F. B. C. Beed, M.A.., F.G.S., in an appendix, gives a list of 

 the fossils found by the authors, and offers some remarks upon the 

 age of the deposits. 



XIX. Intellience and Miscellaneous Articles. 



MEASUREMENT OF ELECTROLYTIC CONDUCTIVITY BY 

 CONTINUOUS CURRENTS. 



To the Editors of the Philosophical Magazine. 

 Gentlemen, 



TN your June number (p. 464) Dr. Neesen writes to say that 

 -*- Dr. Henderson and I made no mention of his name in a paper 

 on " A Satisfactory Method of Measuring the Conductivity of 

 Electrolytes by means of Continuous Currents " published in 

 No. 260 of your Journal. 



We must in the first place express great regret at having 

 altogether overlooked Dr. Neesen's paper in Wied. Ann. vol. xxiii. 

 p. 482. Some excuse for the omission may be found in the fact 

 that no reference to the paper is to be found in AVinkeJmann's Hand- 

 buch (1895) where scores of papers on the measurement of electro- 

 lytic conductivity are mentioned. There is, however, as I have 

 just now found, a reference to it among the Nachtrage in Wied- 

 mann's Electricitdt, iv. p. 1326. No allusion is made even there 

 to Dr. Neesen having devised any special method of using con- 

 tinuous currents for the measurement of electrolytic resistances. 



We willingly concede to Dr. Neesen the credit of having 

 conceived before ourselves the idea which underlies a part of the 

 method which we adopted. Nevertheless we feel that we may claim 

 that the " satisfactoriness " of the method is in large measure due 

 to ourselves. Dr. Neesen succeeded in attaining an accuracy of 1 

 in 1000 for the special case of solution of sulphate of iron with iron 

 electrodes. We succeeded in attaining a much greater accuracy 

 with Pt plates in dilute sulphuric acid or KC1 solution, which 

 Dr. Neesen must admit is quite a different thing. 



There are three ways known to us of diminishing the disturbing 

 effects of polarization in the use of continuous currents : — 



(1) The use of so-called non-polarizable electrodes. 



