164 V. WALFRID EKMAN. 



1. The Apparatus and its Use. 



The current-meter has been constructed with a special eye 

 to the supposed necessity for extreme sensitiveness. The current 

 is measured by the displacement of a pendulum hanging freely 

 by a thread, the pendulum being arrested in situ by a mes- 

 senger simultaneously with a magnetic-needle, which subse- 

 quently indicates the direction of the displacement. To the 

 pendulum, which is furnished with 6 wings acting as surfaces of 

 resistance to the current, is also attached a hollow glass float of 

 sufficient buoyancy to keep the pendulum floating. By means of 

 a weight, movable along the pendulum rod, it is thus possible to 

 obtain any degree of sensitiveness, from the very greatest when 

 the pendulum is suspended almost floating in the water, down 

 to that in which the weight is placed near the lower end of the 

 pendulum. 



Of former apparatuses, this therefore most resembles Aimé's 

 current-indicator, being, however, superior to it in the three fol- 

 lowing particulars : (1) that even in weak currents no error 

 can arise through the torsion of the line; (2) that if desired this 

 instrument can be made more sensitive than the current-indica- 

 tor, and (3) that it measures at the same time the force of the 

 current. 



As regards the details, they will be most clearly seen from 

 the drawing on PI. XV, to which Ihe following description may be 

 added. 



The frame of the apparatus is made of two round brass rods, 

 a, a, united below by the beam h, and above by the cross-piece, c. 

 By a screw-bolt through the last-named piece, the apparatus is 

 attached to the line, which ends suitably in a thimble. In the 

 experiments hitherto made, a bronze line was employed, but a 

 single metal cord is clearly the most practical. In the eyes 

 at the bottom of the frame hangs a lead for the purpose of 

 stretching the line, and quickly l)ringing the apparatus into its 

 position of equilibrium, if the current should have taken it on its 



