338 SEC. 10. ELECTRICITY. 



35. Magneto induction bell, similar to the above. 



36. Ditto ditto. 



37. Magneto inductor of 6 magnets, without bell. 



38. Dynamo-electric exploder for low tension (quantity) fuses, used for 

 blasting and torpedo firing purposes. 



This apparatus consists of an ordinary Siemens' armature, which is caused, 

 by the turning of a handle, to revolve between the poles of an electro- 

 magnet. The coils of the electro-magnet are in circuit with the wire of the 

 armature, and the residual magnetism of the electro-magnet cores excites at 

 first weak currents, which pass into the electro-magnet coils, increasing the 

 magnetism of the core and inducing still stronger currents in the armature 

 wire, to the limit of magnetic saturation of the iron cores of the electro- 

 magnets. 



By the automatic action of the machine this powerful current is sent into 

 the wire or cable leading to the fuse. The fuse is practically either an inter- 

 ruption of the cable circuit or a great increase in its resistance at some point, 

 by the interposition of a badly-conducting substance ; the consequent action 

 is that either an electric spark passes between the interrupted portions of the 

 conductor, or the piece of bad conductor is highly heated, causing ignition of 

 the explosive substance contained in the fuse. 



The coils, whether of armature or electro-magnets, of the quantity exploder 

 are wound with wire of large diameter to a total resistance of 8 to 10 units in 

 about 2,000 windings ; electric currents possessing great heating power, but of 

 low intensity, are therefore generated by this machine. 



39. Dynamo-electric exploder for high tension fuses, also called spark 

 fuses (intensity). 



The construction is similar to the above, but this exploder has its coils, 

 both of the armature and the electro-magnets, wound with fine wire to a total 

 resistance of 2,000 to 2,500 Siemens' units, in about 17,000 windings. Upon 

 causing the armature to revolve, currents are generated of great intensity, 

 and an electrical spark passing between the separated conductors in the fuse 

 inflames the explosive priming. 



40. Case of electric cable samples. 



41. Ditto ditto. 



42. Ditto ditto. 



1751. Polar-light Apparatus. 



Professor Lemstrom^ Helsingfors, Finland. 



Report of a speech of Dr. Lemstrom on his Polar-light apparatus, and the 

 theory of the Polar-light. 



This apparatus serves to prove that the polar light or aurora borealis is an 

 electric current flowing from the higher regions of the atmosphere down to 

 the earth. 



A sphere of brass, fixed on a bar of india-rubber or ebonite 0-6 meter 

 long, which is screwed in the board of the cross-shaped foot. A cylinder of 

 india-rubber, 3 meters long, is fixed to the same board at about 0-7 meter 

 from the sphere. From the cylinder comes out a branch with a bow, both of 

 india-rubber. On the bow are fixed 16 Geissler's tubes, wherein the air has 

 a pressure of about 0-5 millimeter. The lower ends of the tubes are pierced 

 by platinum wires, which are directed towards the sphere, whilst at the upper 

 end the platinum wires are, by means of their copper wires, in a metallic union 

 with a button, and also in metallic union with the earth. From underneath 

 the sphere a copper wire, well isolated with india-rubber, leads to the negative 



