374 Dr. Lamont on the most advantageous Form of Magnets. 





Magnetic moment. 



Mass. Proportion to the mass. 



A 





44-6 



372 1-20 



B 



... 



34-3 



28-8 1-19 



C 



• • 



27-7 



23-6 1-17 



D 



. 



23-6 



18-0 1-32 



This series of observations is not very decisive ; nevertheless it 

 shows distinctly that the pointing of the ends of the magnets is 

 not advantageous, except when the diminution of the breadth 

 begins from the middle. A flat needle contracting its breadth 

 from the middle to a point is, by the above measures, more 

 advantageous by one-tenth than one of the form of a parallelo- 

 gram ; from other far more decisive series of experiments I have 

 found a somewhat greater proportion, i. e. one-eighth. 



7th Series of Experiments. — It is known that magnetism 

 shows its strength in corners and points, and it appeared proper 

 to investigate what result would be obtained if a magnet had 

 several points. With this view, three parallelograms of 47"'-0 

 length, 9"'-0 breadth, 0'"*4 thickness, were cut out of a plate of 

 iron, and triangular notches were cut out of the ends, so that 

 one piece received two, the other three points at each end, whilst 

 in the third piece no cut was made. The form of the pieces is 

 seen in fig. 10 ; the depth of the cuts amounted to a fourth 

 of the length. The observation gave — 





Magnetic moment. 



Mass. Proportion to the mass. 



A . 



. . 5-075 



1-00 4-659 



B . 



. . 4-908 



1-10 4-462 



C . 



. . 6-005 



1-41 4-259 



According to this it is advantageous to cut notches in the ends 

 of flat magnets, and the proportion increases with the number 

 of notches. 



As a consequence of the determination given in the sixth 

 series of experiments, the proportion-number would be 4 - 79 for 

 a needle contracting to a point from the middle; it is not im- 

 probable that by increase of the number of notches this pro- 

 portion could be exceeded, nevertheless the figure recommended 

 itself, as to what is here in question, so little in other respects, 

 that it will scarcely find practical application. 



From the preceding determinations it results — 



(1) That narrower magnets are more advantageous than 

 broader. 



(2) That thinner magnets are more advantageous than thicker. 



(3) That consequently the most advantageous form is that 

 in which breadth and thickness disappear, and the magnet is 



