Gold for Weak Magnetic Fields. 75 



the two rows of teeth. Small drops of solder were let fall 

 from a hot soldering-bolt so that they formed a connexion 

 between the gold and the copper points. The solder dissolved 



Fig. 2 



SoioEfx •■-*:: 



a 



I Co/T&EA/r 



Hi 



Area of Coil 



| ro*- I 



DCTERMINATION 

 \OfSTItCNCm I 



I 



,0 







SoiOE/f 



area of Magnet Core 



Gap 3 cms. 



some of the gold as before, but as the hot drops were already 

 more or less spherical they did not draw away from the gold 

 before they were cooled by conduction of heat into the 

 copper. This gave a perfect connexion. The secondary 

 electrodes — wires soldered to screws driven into the ebonite — 

 were similarly attached to the gold. A very thin coat of 

 shellac was now spread over the surface of the foil, to prevent 

 its being torn by the circulating kerosene in the constant- 

 temperature bath in which the measurements were made. 



To measure the magnetic field, a coil of 18 turns *, fixed to 

 a sheet of mica, was held by clamps just in front of the 

 central portion of the gold plate. Its area was 2*05 x 8*30 

 sq.cms., so that it nearly covered the active portion of the 

 gold. This was put in series with a ballistic galvanometer, 

 of the D'Arsonval type, an earth-inductor, and a resistance- 

 box. 



The ebonite plate-support, with its attached foil and coil, 



* One of 100 turns was necessary at the lowest fields 



