Intelligence and Miscellaneous Articles. 397 



decrement of the tuning-fork's vibrations, does not sensibly come 

 into consideration with respect to the length of a vibration — not 

 even in the cases of mercury and glycerine, although in the former 

 the density, and in the latter the viscosity is very great. — Annalen 

 der Physih und Chemis, 1878, No. 1, pp. 157-160. 



A NOTE ON EXPERIMENTS WITH FLOATING MAGNETS ; SHOWING 

 THE MOTIONS AND ARRANGEMENTS IN A PLANE OF FREELY 

 MOVING BODIES ACTED ON BY FORCES OF ATTRACTION AND 

 REPULSION, AND SERVING IN THE STUDY OF THE DIRECTIONS 

 AND MOTIONS OF THE LINES OF MAGNETIC FORCE. BY ALFRED 

 M. MAYER. 



For one of my little books of the Experimental-Science Series I 

 have devised a system of experiments which illustrate the action 

 of atomic forces, and the atomic arrangement in molecules, in so 

 pleasing a manner, that I think these experiments should be 

 known to those interested in the study and teaching of physics. 



A dozen or more of No. 5 or 6 sewing-needles are magnetized 

 with their points of the same polarity, say north. Each needle is 

 run into a small cork, J in. long and -fy in. in diameter, which is 

 of such size that it just floats the needle in an upright position. 

 The eye end of the needle just comes through the top of the 

 cork. 



Eloat three of these vertical magnetic needles in a bowl of 

 water, and then slowly bring down over them the north pole 

 of a rather large cylindrical magnet. The mutually repellent 

 needles at once approach each other, and finally arrange themselves 

 at the vertices of an equilateral triangle, thus .-. . The needles 

 come nearer together or go further away as the magnet, above 

 them, approaches them or is removed from them. Vibrations of 

 the magnet up and down cause the needles to vibrate ; the triangle 

 formed by them alternately increasing and diminishiug in size. 



On lifting the magnet vertically to a distance, the needles mutu- 

 ally repel and end by taking up positions at the vertices of a tri- 

 angle inscribed to the bowl. 



Eour floating needles take these two forms 



Five 

 Six 



V 5J J) )? )» 



'> 5? JJ ?J 5? 



Seven „ „ „ the form • • • 



I have obtained the figures up to the combination of twenty 

 floating needles. Some of these forms are stable ; others are un- 

 stable, and are sent into the stable forms by vibration. 



