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Scientific Intelligence. 427 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



F 



1. Laics of Magnetism, — Tyndal has studied the laws which govera 

 the attraction of an electro-magnet upon a spherical nriass of soft iron. 

 The apparatus employed, consisted of an electro-magnet in the form of 

 a straight bar 10 inches in length and IJ inches in thickness, and 

 wound with 360 feet of copper wire ; this magnet was placed vertically 

 under one extremity of the beam of a balance from which was sus- 

 pended a sphere of soft iron, in such a manner that when the sphere 

 rested upon the end of the magnet, and the copper suspension wire 

 was lense, the balance beam was exactly horizontal. Weights were 

 placed in a scale pan attached to the opposite end of the beam so as to 

 hold the sphere of iron in perfect equilibrium ; in this manner the effect 

 of the weight of the sphere was eliminated. The eleciro-magnet form- 

 ed part of a circuit comprising also a galvanic battery, a tangent's 

 compass, and a rheostat. In experimenting, a known weight was placed 

 m the scale pan opposite the sphere, and then by means of the rheo- 

 stat the force of the current, and consequently the attraction o{ the 

 niagnet, was gradual!y diminished till the sphere separated from the 

 surface of the magnet; at this instant the angular deflection of the 

 needle of the tangent's compass was noted. In this manner the at- 

 tractive force corresponding to a given intensity of the current is di- 

 rectly expressed by weight. The principal results oblained by the 

 author in this investigation are as follows: 



(!■) The mutual attraction between an electro-magnet and a sphere 

 of soft iron in immediate contact with each other, is directly proportional 

 to the force of the magnet or of the magnetizing current. 



{-i-) If a constant force be applied to the sphere in a direction oppo- 

 site to that in which the attraction of the magnet is exerted, the attrac- 

 tive force of the latter must vary Inversely as the square roots of the 

 distances in order lu hold the sphere in equilibrium when its distance 

 from the magnet varies. 



(3.) The mutual attraction between a sphere of soft iron and a mag- 

 net called into action by a constant current, is inversely as the distance 

 between the sphere and the magnet. 



(4.) The mutual attraction between an electro-mngnet and a sphere 

 of soft iron, when the two are separated from each other by a deter- 

 niinate distance, is proportional to the square of the induced magnetism. 



P^gg. Ann.^ Ixxxiii, 1. 



2. Magnetism of Oxygen gas, — Pluckeh has given the results of a 

 comparison of the magnetism of oxygen with that of iron. A glass 



globe was filled with oxygen of the same tension as the surrounding 

 air. The amount of attraction exerted by an electro-magnet npon this 

 globe was then determined by means of a very delicate balance. The 

 globe was then emptied and filled with a solution of chlorid of iron, 

 snd the magnetic attraction again determined in the same manner. 

 The atlraciioa upon the oxygen was found to be to that on the solution 



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