April 2 2, 1880] 



NATURE 



595 



become grey as soon as the velocity is six or seven turns 

 in a second. 



It is possible also to obtain motion without the presence 

 of magnets by guiding an impulse to the movable by an 

 exterior force, and M. de Fonvielle and M. Lontin 

 insisted on that particular point in the memoir they have 

 presented jointly to the Paris Academy in offering a 

 theory of these curious phenomena. The rotation is 

 not always the same, but' once it is determined in a 

 solid sufficiently balanced it continues indefinitely in the 

 same direction. The direction does not change when we 

 reverse the direction of the currents by means of a 

 commutator. 



The possibility of producing the same movement by 

 means of movables of any form whatever, in presence of 

 magnets or without their action, and notably of two spirals 

 constructed of aflat wire and wound in an opposite direction, 

 appears to the inventors to demonstrate that the rotatory 

 action is exercised individually on each molecule of iron, and 

 that the total impulse must be regarded as the integral of the 

 individual impulsive actions. This remarkable property 

 appears to furnish a very simple means of completely 

 explaining all the circumstances of these curious phe- 

 nomena by means of the known laws of induction, and to 

 dispense with having recourse to any new hypothesis. It 

 is sufficient, in fact, to remark that the molecule of iron 

 acts in its movement of rotation in two different ways in 

 each of the two nearly equal currents of induction which 

 successively traverse the spires. In fact, during the whole 

 continuance of the two phases of rotatory movement which 

 the galvanometric frame brings closer together, each mole- 

 cule of soft iron increases the intensity of the current 

 which affects it, and which the inventors call positive, in- 

 dependently of its real direction, in order tc fix the idea ; 

 at the same time it diminishes that of the current which 

 repels it, and which they call negative, for the same rea- 

 sons. In the two other phases of its movement the same 

 molecule diminishes the intensity of the positive current, 

 which then tends to draw it back, and increases that of 

 the negative current, which turns it away from the frame. 

 The actions exerted in the two phases of the movement, 

 that is, in the total extent of the plane described by the 

 molecules, tend then to keep up the continuous rotation, 

 which progressively increases in speed until it reaches 

 that which corresponds to the absolute intensity of the 

 attractions or repulsions exercised by the currents in- 

 duced, by the energy of the inductive current, the value 

 of the friction of the resistance of the arc, &c. 



When we bring the pole of a magnet into action, it is 

 clear that its influence determines in each of the mole- 

 cules of the movable object a transient magnetisation 

 which strengthens the induction currents produced in the 

 spires in the cases in which it is concordant, and which 

 paralyses them in the opposite case. It hence results 

 that, in presence of a permanent magnetic centre, the 

 movement is possible only in a direction determined bv 

 its position and its nature. MM. Ue Fonvielle and Lon- 

 tin believe that this principle applies even to the action of 

 the earth. 



When we change the position of the active pole in 

 relation to the axis of rotation, the rotation changes its 

 direction ; but the pole of the magnet may be placed 

 above or below, to right or left, without the rotation 

 changing its direction. The two poles of a bar or a 

 horseshoe magnet combine to accelerate the movement 

 when they arc placed in the direction of the frame ; but 

 if we place the magnet in a perpendicular direction, all 

 movement is, as a rule, rendered impossible. It is the 

 same with near position ; in proportion as we approach it 

 to that limit of position, the rotation in general will be 

 found to slacken. It is clear that a magnetisable body 

 so strongly tempered as not to have the capacity of being 

 magnetised and demagnetised to the given extent, will 

 remain insensible to these successive dynamic reactions, 



and consequently immovable, and that it is necessary to 

 employ the softest possible iron in the construction of the 

 movable objects. The same phenomena, especially with 

 the spiral, may evidently be produced if we place it about 

 the frame. They are accompanied, especially with the 

 full disk, by a strident sound, by alternate magnetisations 

 and demagnetisations. Their production appears to the 

 inventors a new confirmation of the theories which they 

 have advanced. 



We must add that the coil used is of a peculiar con- 

 struction, but that at least some of the phenomena can be 

 observed without any'Ruhmkorff's machine at all, but with 

 an interrupter of the current from the battery. 



It is impossible to say at present if the apparatus may 

 be rendered serviceable as a motive power. But it may 

 be used at all events not only as exhibiting a new mode 

 of action, but as a balance to make a comparison of the 

 force of several magnets, by placing them in opposition 

 at various distances. 



NOTES 

 McCtILL University, Montreal, has long held the lead in the 

 cultivation of natural science among the colleges of Canada, and 

 has already large collections, which are .'till further to be 

 increased by the liberality of Mr. Redpath, a member of the 

 Board of Governors, and Principal Dawson. Mr. Redpath 

 proposes to erect on the College grounds, and on a site which 

 will harmonise with the arrangement of the existing buildings, 

 a stately and beautiful edifice for a museum of geology and 

 natural history, primarily for the use of the professors and 

 students of the college, but also for the benefit of the public 

 generally. The building is to be detached and practically fire- 

 proof, and while it will be an ornament to the college grounds, 

 will be fully up to the present idea of museum buildings in regard 

 to space, light, and means for study and illustration. It will 

 accommodate the whole of the present collections of the Uni- 

 versity, and will enable them for the first time to be fully 

 acces-iUe to students. In connection with Mr. Redpath's gift, 

 Principal Dawson purposes to present to the University the whole 

 of his private collections in geology, embracing the types of the 

 species which have been described by him in his papers and other 

 publications. In some departments of the geology of the 

 Dominion, as in the fossils of the Pleistocene and Carboniferous, 

 and in the geology of the Maritime Provinces, these collections 

 are believed to be the most important extant. 



The International Congress of Anthropology and Prehistoric 

 Archxology holds its next meeting at Li-bcn, on .September 

 20-20, this year. Several important questions concerning the 

 prehistoric archaeology of Portugal will be discussed. Excursions 

 will be made to several places of archaeological interest. 



A universal exhibition of prehistoric German anthropology 

 will take place at Berlin in August. All the German States have . 

 been invited to join in this exhibition, which will comprise objects 

 chosen from every museum in Germany. Pr .f. Virchow is at 

 the head of the Committee appointed to organise the necessary 

 details. 



The Institution of Mechanical Engineers holds its ordinary 

 general meeting to-day and to-morrow, April 23, at 7.30 p.m. 

 The following papers will be read and discussed : — " Remarks 

 on Chernoff' s Papers on Steel," by Mr. William Ander-on, of 

 Erith ; " On Permanent Way for Tramways, with special re- 

 ference to Mechanical Traction," by Mr. J. D. Larsen, of 

 London ; " On Water-Pressure Engines for Mining Fur- 

 by Mr. Henry Davey, of Leeds; "On Electric 

 Lighting" (second paper), by Dr. John Hopkinson, F. R.S., 

 of London 



