Miscellaneous. 



305 



should be considered simply as occupying the range of the ordinary 

 mechanisms which serve for the transmission or transformation of 

 the velocity, without increasing the available power. So it would be 

 possible to use, instead of the ordinary wheelwork, rods of greater or 

 less length, or a greater or less quantity of wire, in order to establish be- 

 tween the force and the velocity, the relation which the applications to 

 manufacturing processes may require. 



"3rd. The mean attraction of the magnetic rods, or the pressure 

 which the machine can exert, is proportional to the square of the cur- 

 rent. This pressure is indicated by the galvanometer, which in this man- 

 ner performs this function of the manometer of steam-engines. 



" 4th. The economic effect, L e. the duty or the available power, divid- 

 ed by the consumption of zinc, is a constant quantity, which is exposed 

 most simply by the relation between the electro-motive force and 

 the factor k, which has been previously noticed. I may here repeat, 

 what I stated elsewhere, that by employing platinum instead of copper, 

 the theoretical expenses may be reduced in the proportion of nearly 

 23 to 14. 



" 5th. The consumption of zinc, which takes place while the machine 

 is at rest, and does no work at all, is double that which takes place, 

 while it is producing the maximum of power. 



" I consider that there will not be much difficulty in determining with 

 sufficient precision the duty of one pound of zinc, by its transformation 

 into the sulphate, in the same manner that in the steam-engine, the 

 duty of one bushel of coal serves as a measure to estimate the effect of 

 different combinations. The future use and application of electro- 

 magnetic machines appears to me quite certain, especially as the mere 

 trials and vague ideas which have hitherto prevailed in the construction 

 of these machines, have now at length yielded to the precise and 

 definite laws which are conformable to the general laws which nature 

 is accustomed to observe with strictness, whenever the question of effects 

 and their causes arises. In viewing on the one hand a chemical effect, 

 and on the other a mechanical effect, the intermediate term scarcely pre- 

 sent itself at first. In the preseut case, it is magneto-electricity, the 

 admirable discovery of Faraday, which we should consider as the re- 

 gulating power, or, as it may be styled, the logic of electro-magnetic 

 machines." 



Prof. Forbes congratulated the Section on the advance made towards 

 introducing electro-magnetism among our useful moving powers. Here 

 was a boat, twenty feet long, capable of containing fourteen people, 

 propelled by it on the Neva, at the rate of three miles an hour : a more 



