490 M. Becquerel on a new Electro-magnetic Engine 



Any electro-magnetic engine . must be composed essentially 

 of a series of electro-magnets of soft iron, of armatures also of 

 soft iron, or arranged as electro-magnets, with various adjuncts, 

 for tbe transmission of the electricity furnished by a battery or 

 electro-magnetic machine, and of a commutator or breaker, for 

 the purpose of producing a continuous circular or backward and 

 forward motion. 



In the machines hitherto constructed, these various parts do 

 not combine all the conditions desirable for making use of all 

 the power set in action ; a cheap, constant, and powerful source 

 of electricity does not yet exist ; the soft iron, never being pure 

 or perfectly malleable, retains for a longer or shorter peiuod 

 after each interruption a portion of the magnetization which 

 had been communicated to it by the current; the primitive 

 current and the extra current produce contrary effects, causing 

 a mutual injury ; and the commutators often present alterations 

 when the circuit is closed. » 



M. Jacobi, moreover, wno has carefully studied the subject of 

 the practical employment of electro-magnetic engines, has 

 arrived at this result, — that the mechanical effect or amount 

 of work, considering the expenses necessary to keep them in 

 action, is far inferior to that of the other motive powers in use. 

 But this does not set the question at rest ; for, if we succeed in 

 discovering sources of electricity more oeconomical and powerful 

 than those at present in use, and in avoiding a portion of the 

 inconveniences already mentioned, electricity and magnetism 

 may take their place with heat as motive forces. 



These considerations show that all researches having for their 

 object the removal of some of the difficulties encountered in the 

 emplojmient of electricity as a motive power, should be received 

 favourably; and the memoir recently presented by M. Marie 

 Davy to the Academy contains some new views worthy of atten- 

 tion, as will be seen from the following report. 



M. Marie thought, and with reason, that, in order to obtain 

 the maximum of effect in electro-magnetic engines, the electro- 

 magnets and the armatures must act up to the point of contact, 

 seeing that the electro-magnetic force, as he found by calcula- 

 tion and experiment, decreases so rapidly with the distance, that 

 in employing two electro-magnets, when these are brought to- 

 gether from a distance to the point of contact, they develope an 

 amount of work in such a manner that five-sixths are produced 

 in the last millimetre, and the half of the remainder in the last 

 but one ; when the second electro-magnet is replaced by an 

 armature of soft iron, three-fourths of the quantity of work are 

 produced in the last millimetre through which the armature 

 passes, and more than half the remainder in the last but one. 



