262 Capt. H. B. Jackson. On some Phenomena [May 1, 



Thirdly, the rocks containing iron ores : — In all these cases a greater 

 loss of proportional distance is recorded than in the others — and it was 

 exceptional to receive any signals at all — and the best result recorded 

 in several trials was but 39 per cent, of the open sea distance (fig. 5). 



1,000 

 500 





signals. 



k 



1 ' 







Distance 



in nautical 



miles. 







i 



50 





100 



150 



IflOO- 

 6O0] 

















1 

















i | 

 50 



(5) 



100 





I.OOO-. 

 500; 







i T i 

















i 



10 



ao 



(6) 



40 





50 







I No 







T 





ipoo 



500 



signals. 



The results shown in fig. 6 are the most conclusive that I have 

 obtained in proving the screening effect of hard rocks containing iron 

 ores on the passage of electric waves through land. The pinnacle of 

 rock shown therein represents an extremely precipitous, narrow, but 

 high promontory jutting out from the mainland and rising abruptly 

 out of the sea, to which it is steep to, so that the ship could pass close 

 to it in perfect safety at a distance of about 100 yards. 



To ascertain the effect of this wedge-like obstruction, the ship was 

 steered close to the land, and her position was carefully noted when 

 signals ceased or commenced. These signals were being sent con- 

 tinuousty from another vessel (distant 18 miles) during the whole 

 period of the trials, the letter F ( , in Morse Code) being 



