174 Professor TyndalVs further Researclies 



IX. 



Cylinders of Calcareous Spar. 



Length 3 inches. Diameter 0*7. 



Current direct. Current direct. Current direct. 



Position 1. 699-5 Position 2. 698*5 Position 3. 697*5 



Here, asin the other cases, the deflection was permanent, and could 

 be augmented by the suitable raising or lowering of the respect- 

 ive cylinders. The action is small, but perfectly certain. The 

 magnet was steady and moved promptly and invariably in the 

 directions indicated by the numbers. It will be observed that 

 the deflections are the same in kind as those produced by bis- 

 muth. 



The intrusion of other employments compelled me to post- 

 pone the continuation of these experiments for several weeks. 

 On taking up the subject again, my first care was to assure 

 myself that the instrument retained its sensibility. Since the 

 experiments last recorded it had been transported over several 

 hundred miles of railway, and hence the possibility of a disturb- 

 ance of its power. The following experiments, while they cor- 

 roborate the former ones, show that the instrument retained its 

 power and delicacy unimpaired : — 



X. 



Bismuth cylinders. 



Current direct. Current reversed. 



Position I. 612 264 



Position 2. 572 230 



Position 3. 526 200 



The deflections, it will be observed, are the same in kind as 

 before ; but by improved manipulation the effect is augmented. 

 In passing from position 1 to 3 we have here a deflection 

 amounting in one case to 64, and in the other to 86 divisions of 

 the scale. 



To Mr. Noble I am indebted for two cylinders of pure sta- 

 tuary marble; the examination of these gave the following 

 results : — 



XI. 



Cylinders of Statuary Marble. 



Length 4 inches. Diameter 0*7. 



Current direct. Current reversed. 

 Position 1. 601 215 



Position 2. 598 218 



Position 3. 596 220 



Here, in passing from position 1 to 3, we have a permanent 



