168 



Prof. C. Pritchard. On the Capacities of two [May 3, 



the metal, there remained only a solution of Fe 2 Cl 3 , in which the mag- 

 netised bar A gradually assumed its normal electro-positive position ; 

 this reaction is exemplified by the results in Table C, Col. 4, Divi- 

 sion II. The comparative non-activity of HCi on magnetised bars is 

 very singular, and at present unaccountable. In conclusion, I may 

 state that this research has shown that a current flows from a mag- 

 netised bar towards an unmagnetised one, when the two are immersed 

 in suitable solutions, and that the result was dependent both on the 

 nature and strength of the solution, and also on the extent of the 

 magnetisation of the metal. It has also been demonstrated that when 

 a magnetised rod constitutes one element in a suitable electrolyte 

 acting upon it, local currents flow from the more highly magnetised 

 polar terminals towards the less magnetised or neutral equatorial 

 portions. These conditions would cause the magnetised rod to be 

 more generally acted upon by the electrolyte, the composition of the 

 solution surrounding it being thereby also affected, and to a con- 

 siderable extent this might account for its electro-positive position 

 compared with the unmagnetised rod, otherwise under the same 

 conditions. Observations have also been made on the influence of 

 magnetisation in relation to the passive state of iron in nitric acid, 

 with interesting results. In the present state of the inquiry it is 

 preferable to confine oneself to a simple record of facts ; I think, how- 

 ever, it has been clearly demonstrated in course of the numerous and 

 varied experiments of this research, that the magnetisation of iron 

 and steel influences the action of reagents upon the metal. 



Y. " Report on the Capacities, in respect of Light and Photo- 

 graphic Action, of two Silver on Glass Mirrors of different 

 Focal Lengths." By the Rev. C. Pritchard, D.D., F.R.S., 

 Savilian Professor of Astronomy, Oxford. Received April 

 18, 1888. 



In May of last year, I was requested by a Committee on stellar 

 photography, appointed by the Council of the Royal Society, to 

 examine the comparative photographic capacities of two silver on 

 glass mirrors, each having an aperture of 15 inches, but of different 

 focal lengths, viz., 80 inches and 120 inches respectively. In the 

 present report these will be designated by the symbols i^-inch and 

 y^-inch. The mirrors in question were provided by the generosity of 

 Dr. Warren de la Rue. Various unforeseen difficulties incidental to 

 pioneering in a science still in its infancy have intervened, unavoid- 

 ably impeding the progress of the enquiry. The chief among these 

 have been : — 1. The comparatively imperfect automatic mechanism 

 of the driving apparatus attached to the telescope carrying the 



