804 Prof. A. Righi on Magnetic 



§ 17. It seems, therefore, that the simple instrument de- 

 scribed above shows roughly the same order of accuracy as 

 the standard cylindrical coil. It is simple in construction 

 and use, reliable in results, whilst it possesses two main 

 outstanding advantages : — For a given length of winding it 

 is more sensitive than the circular form, and any departure 

 from trueness in form can be readily and exactly allowed for. 



The writer's thanks are due, and are tendered, to Professor 

 E. Taylor Jones, whose help and counsel have been conti- 

 nually placed at his disposal ; and to Mr. J. A. Hughes, 

 B.Sc, who has given valuable assistance in recording and 

 reducing the observations detailed in the last section. 



University College of North Wales, Bangor. 

 June 1912. 



{Note added October 1912.) Since writing the above, two 

 interesting papers* by W. Wien and H. Kahle have come 

 before the writer's notice. The papers describe a dynamo- 

 meter, one of the coils of which is rectangular in section. 

 Some of the results given above are there discussed, but the 

 overlapping is not serious, whilst the methods of attacking 

 the problem differ from those in the present paper. 



LXXXI. On Magnetic Rays in Different Gases. 

 By A. RiGHl, Professor of Physics, University of Bologna f. 



I PRESENT in this note some observations on a paper lately 

 published J, in which Messrs. L. T. More and E. R. Rieman 

 give an account of some experiments concerning the magnetic 

 rays. _ 



As is known, my researches were always made with tubes 

 containing rarefied air ; and the two authors, repeating them, 

 have confirmed entirely my results, including the disap- 

 pearance (first noted by me) of the magnetic rays when the 

 magnetic field becomes too intense §. They have, on the 

 other hand, in some cases obtained different results by intro- 

 ducing other gases into the tubes in place of air ; and hence 

 they find reason, if not to contest, at least to throw some 

 doubt on the theory proposed by me to explain the phenomena 

 presented by the magnetic rays. 



* Wied. Ami. 1896, vol. lix. 

 + Communicated by the Author. 

 % Phil. Mag. No. 140, p. 307. 

 § Loc. cit. p. 312. 



