788 Mr. A. Ferguson on the Construction and 



are produced from two paper electrodes because very few 

 /3 rays are excited in the paper ; bat § rays are excited from 

 a paper electrode opposite a gold electrode because the 

 rays from the latter can fall on the former. This result 

 was, of course, to be expected. The emission of § rays from 

 a solid is equivalent to ionization in a gas, and since there is 

 no evidence of the production of ions by Rontgen rays, 

 except by means of the j3 rays to which they give rise^ it 

 was to be expected that no g rays should be excited in a 

 substance by Rontgen rays except when B rays also fall 

 on it. 



Summary. 



The important conclusions of this paper are given at the 

 end of § 5 and of § 8. 



Leeds University, July 1912. 



LXXX. The Construction and Constants of a Rectangular 

 Galvanometer. By Allan Ferguson", B.Sc. {Lond.), 

 Assistant Lecturer in Physics in the University College o; 

 North Wales, Bangor*. 



Summary of Contents. 



§ 1. Description. 



§ 2. Constant of a ' single turn ' galvanometer. 



§ 3. Comparison of square and rectangle. 



§ 4. Comparison of square and circle. 



§ 5. Variation of field-intensity near centre of square. 



§ 6. Calculation of field-intensity at points on axis of rectangle 

 perpendicular to its plane. 



§ 7. Calculation of constant of ' strip ' galvanometer. 



§ 8. Calculation of constant of ' single-layer ' galvanometer. 



§ 9. Equivalence of single layer winding and current sheet. 

 § 10. Constant of ' multiple-layer ' galvanometer. 

 § 11. Calculation of the ' Helmholtz ' condition. 

 § 12. Irregularities of winding. 

 1 13. Correction for inequalities in sides of frame. 

 § 14. Correction for finite curvature at corners of square. 

 § 15. Temperature correction. 

 § 16. Experimental results. 

 § 17. Conclusion. 



§ 1. rjlHE instrument described below was intended 

 JL originally to afford a laboratory exercise for the 

 verification of the relation 



F=2 -A + i + I + 1 Y (i . } 



\Pl P2 P3 Pj 



* Communicated by Prof. E. Taylor Jones. 



