408 Intelligence and Miscellaneous Articles. 



M. Chwolson, of St. Petersburg, and somewhat later M. Schering, 

 of Grottingen, attempted to modify the theory of the deadening of 

 a magnet oscillating in a galvanometer, assuming that its sensitive- 

 ness varied with the angle. M. Chwolson, moreover, in his memoirs 

 on this subject {Memoir es de VAcademie imperiale des Sciences de St. 

 Petersbourg, vol. xxvi. No. 4, 1879, and vol. xxvii. No. 3, 1880), 

 gave a determination of the functions of the two galvanometers 

 which I had employed in my researches, and then deduced from his 

 theory the corrections to be applied to my results. He thus found 

 that the difference between the indications of the induction-com- 

 pass and the ordinary needle-compass were reduced, for one of the 

 instruments from 15' to 0-6, and for the other from 5' to 0*6. 



I, on my part, have attempted to get over this difficulty by ex- 

 perimenting in such a manner as to make the deflections almost 

 equal in the two operations. This is effected by fixing the axis of 

 rotation of the coil in two positions, which make the same angle on 

 the two sides of the direction of the total force of magnetization. 

 The deviation of the deflections of the magnet of the galvanometer 

 are then changed ; but they are almost equal in the two cases, and 

 the difference in sensitiveness with the angular deviations is then 

 eliminated from the result. It is true that, in order to carry out 

 this method, a divided circle must be added to Weber's apparatus, 

 so that the angle of the axis of rotation with the vertical can be 

 read off. If b 1 and b 2 are the angles in the two operations, and (p 1 

 and (j> 2 the constant deflections of the galvanometer, obtained by the 

 method of multiplication, the magnetic inclination i is given by the 

 simple formula 



tan^=M ° S ^~^ C0S \ 

 2 sin &J— ^sini, 



Experiments which I made at the observatory of Pawlowsk 

 (Bulletin de VAcademie des Sciences de St. Petersbourg, vol. xxvii. 

 May 1881) by this method, taking the inclination of the axis of 

 rotation only about 1° from the magnetic dip, gave as the mean of 

 fifteen observations, during the months of June and July 1880, the 

 equation 



Induction-compass — dip circle (Dover) = —0' 51" + 11", 



where +11" represents the mean error of a comparison. 



In 1881 I still further improved this method by using a galvano- 

 meter whose function of sensibility did not much vary; taking in 

 one case the vertical for the axis of rotation (the angle with the 

 direction of the total force is then 90—^'), and in the other case a 

 position which made with the vertical the angle b = 180° — 2i f , in 

 which i' is approximately the inclination of the place. This modi- 

 fication makes the observations far simpler, and the formula then 

 becomes 



iog;=iog»'(i+tofc.J_\ 



V 2(j) i sin 2 v ) 



<j) L being the constant deflection of the magnet for the vertical 



