506 PROF. JACOBI ON THE APPLICATION OF ELECTRO-MAGNETISM 



surface of contact the nature of steel ; there will be a considerable 

 permanent magnetism, and the transient magnetic force, which alone 

 produces the movement, will be weakened in proportion. A num- 

 ber of experiments which I have made upon the magnetic force of a bar 

 of soft iron bent into a horseshoe (of which I shall speak hereafter) 

 has shown me the great disadvantages of oft-repeated shocks, proceed- 

 ing from the sudden contact of the armature. But, if v/e stop at the 

 mechanical principles of magnetism, it may be objected that the active 

 force gained will not be absolutely lost for the purposes of utility; 

 that in part the elasticity of the iron will itself reproduce it ; that an- 

 other portion may be regained by springs properly applied, or by other 

 mechanical methods which may be invented. We leave the appre- 

 ciation of all these factitious means and of these superadditions to those 

 who are in the habit of constructing machines ; they well know their 

 insufficiency, the great loss of working power, and how rapidly all the 

 systems are destroyed, unless the greatest care be paid to the preservation 

 of the active forces. But we must seek the means of this preservation 

 in the nature of the forces themselves. The history of the steam-engine 

 teaches us that its improvement commences with Watt's ingenious idea 

 of stopping the escape of the steam before the piston had accom- 

 plished its stroke, and of causing the steam afterwards to act by its own 

 expansion. Watt understood the subject: all he did was to give to the 

 function P = ((, («), which expresses the action of the steam, such a 



form as / Pds = r P' ds', and thus the active force gained be- 



comes zero, all the prejudicial and destructive vibrations in the machines 

 previously constructed cease, and the power of the motive force is con- 

 verted for the most part into useful action. I must here cite the valuable 

 researches of M. Ponc61et on the construction of hydraulic wheels, — a 

 work founded upon a profound comprehension of the same principles. 



These considerations, at once clear and simple, have induced me to 

 reject entirely every apparatus in which magnetism is applied to pro- 

 duce immediately an oscillating motion ; these constructions being, as 

 we have seen, as inadmissible as they are impracticable of execution on 

 a large scale. 



In the note which I had the honour of laying before the Academy 

 of Sciences of Paris I stated that, in accordance with all experiments, 

 magnetism is a power acting like universal gravitation, solely in some 



function of space. The integral / '^ Mds comparable M'ith the known 



t / o 



a 

 number g, represents the mean action furnished by the attraction of two 



