130 ANNUAL OF SCIENTIFIC DISCOVERY. 



ments are simultaneous, in both localities ; but the direction of the 

 inagnet indicating the disturbances is directly the reverse in Eastern 

 Siberia of the direction in England. 



RESIDUAL MAGNETISM. 



Dr. A. Von Waltenhofen has communicated to Dingier* s Polytech- 

 nisches Journal, an account of a curious magnetic discovery which he 

 has recently made. It is a well-known fact that the magnetism of an 

 electro-magnet does not entirely disappear with the cessation of the 

 magnetizing current. Dr. A. Yon Waltenhofen has, however, ob- 

 served that the amount of this residual magnetism, as it is called, is 

 dependent upon the manner in which the current is interrupted. If 

 this interruption takes place suddenly, the residual magnetism is 

 much less than when it takes place gradually. A still more interesting 

 circumstance has been observed by him, viz : that the residual magnet- 

 ism obtained by suddenly breaking a very strong current, is sometimes 

 of an opposite nature to that previously existing in the electro-magnet. 

 This fact, which he has hitherto only noticed in very soft iron, is of great 

 interest, inasmuch as it furnishes a new and simple proof that magnet- 

 ism is not caused by the separation of two iiuids, but by the motion of 

 magnetic molecules, to which is opposed a certain amount of frictional 

 resistance. With much ingenuity he compares the state of each mag- 

 netic molecule of the electro-magnet to that of a spring which is bent 

 back. If the spring be suddenly released, it will return very nearly 

 to its original position, or even go beyond it. On the other hand, if 

 it be released gradually, it will stop at a point still further removed 

 from its original position. 



"LIQUID STEERING COMPASS" AND "MONITOR COMPASS." 



Two new forms of compass recently devised by Mr. E. S. Ritchie, 

 of Boston, have the following construction : The distinctive pecul- 

 iarities of the liquid compass are an air-tight metallic case within 

 which is placed the magnetic needle, and of such size and weight as 

 to be of very nearly the same specific gravity as the liquid in which 

 it is intended to lioat. The weight is thus removed from the pivot, 

 and friction is almost prevented ; certain modifications being intro- 

 duced to provide against tilting and other emergencies occurring 

 during the motion of the ship. The distinctive principle of the 

 Monitor Compass is the separation of the magnet from the card or 

 index, so that the inagnet may be elevated above the sphere of dis- 

 turbing attraction of the iron of the ship, while the card is brought 

 to a convenient position to be seen by the pilot; and suspending the 

 movable portion in a liquid so as to secure entire freedom from fric- 

 tion, that the needle may obey the polar force, and at the same time 

 great steadiness is secured for the card. 



New Form of Magnetic Needle. At a recent meeting of the Man- 

 chester Philosophical Society, Mr. Joule exhibited a new form of 

 magnetic needle for showing rapid and minute alterations of declina- 

 tion. It consisted of a piece of hardened and polished watch spring, 

 an inch long, and -^ of an inch broad suspended vertically by a fila- 

 ment of silk. The steel was magnetized in the direction of its 

 breadth. He remarked that Professor Thomson had long insisted 



