2-4 SEC. 9. MAGNETISM. 



The mutual (repulsive) action of the two magnets is greatest -when the 

 lengthening extension of the small magnet passes by the magnetic pole 

 sought, provided that the suspended magnet remains perpendicular to the 

 second magnet. To fulfil this condition an auxiliary magnet is used, which 

 ie placed on the other side of the suspended magnet, and which is to produce 

 an equal, but contrary, effect to the second magnet. This method of finding 

 out the poles has been described in Russian in the " Messenger of Mathe- 

 matical Sciences" (Wiestin), and since, in Poggendorff's Annalen, Bd. 152, 

 s. 42. It demands the use of three distinct apparatus: 1st. A "bifilaire" 

 (double thread wire) apparatus for suspending cylindrical magnets. 2nd. A 

 measuring apparatus, having a small magnet that can be moved along the 

 apparatus, while keeping perpendicular to the direction of said movement. 

 The apparatus has two divisional rules, and is supplied with a microscope, 

 two levels, and two small telescopes of short focus. These two apparatus 

 are placed alongside, and parallel to one another, and, approximately, in the 

 magnetic meridian. The third (No. 3) apparatus consists of a divisioned rule 

 placed perpendicularly to the suspended magnet. Along this apparatus may 

 be moved a small magnet, of which the function has been explained above. 

 The second of the apparatus enumerated has been constructed by Mr. Brauer, 

 of St. Petersburg; from the designs of Professor Petroucheffsky. 



1126b. Apparatus for so-called " Normal " Magnetism, 



by Mr. Th. Petroucheffsky, Professor of Physics at the University 

 of St. Petersburg. Imperial University of St. Petersburg. 



An iron cylinder for magnetising, placed symmetrically in a magnetising 

 screw, may receive very different distributions of the free magnetism, accord- 

 ing to the length of the screw, but the distribution does not depend on the 

 strength of the current. The inventor has discovered that the distribution of 

 the'remanent magnetism, or rather the interpolar distance, stands always the 

 same, independently of the length of the screw or the strength of the current. 

 At a fixed length of the screw, the magnetic poles of the electro-magnet and 

 the poles of the remanent magnetism coincide, so that the electro-magnet, 

 placed horizontally and perpendicularly to the magnetic meridian before 

 a sensitive magnetic needle, acts upon it in the fixed direction (say, the 

 direction of the meridian itself) during the circulation of, and after the 

 cessation of, the current ; in the latter case, the poles of the remanent magne- 

 tism act. The poles are then almost at the ends of the magnetising spiral, 

 the length of which is about 0-8 of the iron cylinder, independently of the 

 length and diameter of the cylinder. This arrangement of the poles of the 

 electro -magnets is called " normal." The apparatus used in these researches 

 are composed of two very distinct parts. The first apparatus contains two 

 brass cylinders, surrounded with wire spirals ; by turning one of these 

 cylinders, the number of spirals can be lessened on the one, and increased on 

 the other. Inside one of these cylinders the iron to be experimented upon is 

 placed. This apparatus is set upon a table covered with marble plates moving 

 in two directions, perpendicular to one another. The other apparatus is a 

 needle, called " unipolar," suspended by means of a cocoon thread, with two 

 microscopes. 



1127. Ring of Elias for magnetising artificial magnets of large 

 size. Teyler Foundation, Haarlem. 



A magnet of 28 kilogrammes weight has been recently magnetised by this 

 ring in Teyler's Museum. 



Dr. Elias proposed more than 25 years ago his ring-coil for the production 

 of artificial magnets of all dimensions, by an intense galvanic current. His 



