126 Messrs. Gee and Holden 



on 



which differs only by half a minute from the value obtained 

 when the mirror was in adjustment. 



In like manner the bearing of a pinnacle, as given by the 

 mirror in adjustment, was 128° 40'* 8, while, when the reading 

 for the image of the cross wires was + 5*7 div., it was. 



128°40'-2 + 0'-8 = 128°4i'-0. 



The elevation was 15° 39', and the two results agree to /# 2. 

 It is evident from these test cases that, since the error of the 

 mirror was far larger than that produced by travelling for a 

 day or two, observations in the field can, by means of the 

 scale, be corrected to within the limits of the error of ex- 

 periment. 



The additions to the magnetometer, which we have here 

 described, were made for us by Messrs. Elliott, and we 

 venture to think that they might with advantage be incorpo- 

 rated in standard instruments of the Kew pattern. 



XVI. Experiments on Electrolysis. — Part II. Irreciprocal 

 Conduction. By W. W. Haldane Gee, B.Sc, Lecturer 

 of the Victoria University, and H. Holden, B.Sc, Bishop 

 Berkeley Fellow in Physics, of the Oivens College, Man- 

 chester *. 



[Plate I.] 



WE have observed, when strong sulphuric acid is used 

 as an electrolyte, the electrodes being of platinum, 

 that the decomposition nearly ceases, if by decreasing the 

 resistance in circuit we attempt to increase the current beyond 

 a certain maximum. An investigation of this curious beha- 

 viour has shown that it may best be included with the mis- 

 cellaneous phenomena grouped under the head of unipolar, 

 or, as it may better be called, irreciprocal conduction f. The 

 early experimenters in voltaic electricity devoted much atten- 

 tion to this subject, and it will be desirable to give some 



* Communicated by the Physical Society ; read 26th May, 1888. 



This is the second of a series of papers on Electrolysis and Electrolytic 

 Polarization, descriptive of experiments made since January 1887 at the 

 Owens College Physical Laboratorj 7 -. An abstract of the experiments 

 made, to the end of August 1887, was submitted to the British Associa- 

 tion meeting at Manchester. We desire to acknowledge the assistance 

 received up to that time from Mr. C. H. Lees, B.Sc, Derby Mathematical 

 Scholar of the Owens College. His cooperation has since been discon- 

 tinued, owing to absence at Strasburg. 



t Following Christiani's use of the term, irreciprocal conduction is 

 said to occur if a reversal of the direction of a current causes any change 

 in its magnitude. 



