Intelligence and Miscellaneous Articles. 79 



diminish the dimensions of the rotatory frame, and it is convenient 

 to use a galvanoscope of suitable resistance to which the maximum 

 of sensitiveness is imparted. 



I have for some years tried to realize this experiment by means 

 of an apparatus which can be readily carried about. It consists of 

 an azimuthal circle on which moves an arrangement which supports 

 a ring movable about a horizontal axis ; the angle which this ring 

 makes with the vertical is measured by a vertical circle ; the frame, 

 which is only 0*12 metre in diameter, is supported by the ring and 

 can turn about an axis perpendicular to that of the ring. The 

 dimensions of the instrument do not exceed those of an ordinary 

 dip-needle. 



By a series of systematic trials we can first find the angle of the 

 ring at right angles to the magnetic meridian ; by a second series 

 the axis of rotation of the frame is brought into the direction of the 

 dipping-needle. With the inversions necessary to eliminate the 

 errors of reading, the entire observation does not take half an hoar : 

 this is scarcely the time required to determine the inclination by the 

 dipping-needle. 



As regards the accuracy of the results, it does not appear to be 

 less than that of the dip-circles, the handling of which is so delicate. 

 I will give as an instance some observations recently obtained by 

 M. Morneaux at the observatory of the Pare Saint-Maur. 



Inclination. 



t * , 



Induction Brunner's 



apparatus. compass. 



September 18, 1883 65 21 65 20-7 



29, „ 65 24 65 23*8 



October 16, „ 65 20 65 23-4 



„ 26, „ 65 22 65 18-9 



November 7, „ 65 19 -5 65 17*5 



If it be remembered that the observations were not made simul- 

 taneously, and 'that the results given by dip-needles of different 

 patterns, observed at the same time, scarcely agree better, it will 

 be seen that it is difficult to give any good reason for preferring 

 one method to the other. 



The reading for the magnetic meridian is sufficiently accurate to 

 allow us to determine the declination to within a minute ; hence 

 by adding a telescope we get a true magnetic theodolite. 



I may add that the dimensions of the frame may be still further 

 diminished by introducing soft iron. The induced currents are thus 

 made far stronger without any inconvenience, for the changes of 

 magnetization would still be null for any rotation about the direc- 

 tion of the terrestrial force. — Comptes Eendus, Nov. 26. 



