252 LOCALIZED ELECTRIZATION. 



united by any conducting body, a current will be produced in this 

 outer coil, and will be displayed, at each interruption to the 

 current of the primary coil, by the physical and physiological 

 effects that will be developed in bodies placed within its circuit. 



For an account of the theory of the graduation by the metallic 

 tube B, see further, § IV., C. 



§ IV. — Exiwsition of the p'inciiyal properties of my large donhle- 

 current volta-faradic apparatus, and of the principles icliich have 

 guided me hi its construction. 



A.— The Coils. 



The two coils of the volta-electric apparatus, just described, 

 possess the maximum of their differential physiological properties, 

 by virtue of the proportions of length and thickness that I have 

 given to their respective wires — proportions that I have learnt by 

 experience are the best for this purpose. 



I have laid down that the power of the coils ought to be very 

 considerable under certain circumstances, and experience, or 

 rather the requirements of therapeutics, have compelled me to 

 increase this power more and more. For this reason, the length 

 of my coils, which was at first but eight centimetres, has now been 

 nearly doubled, and the length of their wires has been increased in 

 proportion (to 1000 metres for the fine, and 200 metres for the 

 coarse wire). It would be easy to go beyond the power thus 

 given, but I have not at present seen that it would be useful, and 

 it would perhaps be imprudent. 



Such an increase of strength has necessarily increased the weight 

 of the instrument represented in figs. 52 and 55; but without 

 rendering its bulk more considerable. 



B. — The commutator of the coils. 



In my original instruments, the ends of the wire of ench 

 coil terminated in the metallic knobs (two below for the primaiy 

 coil, and two above for the secondary coil) to which the conductors 

 for the rheophores were affixed. It was therefore necessary to 

 change the attachment of these conductors every time that it was 

 wished to change the coil. Such an arrangement rendered certain 

 experiments difficult, and was very inconvenient in practice. It is 

 much more easy to compare the differential properties of the 

 currents of the two coils when we can pass rapidly from one to 

 the other; and it often happens that it is desirable to employ them, 

 by turns, for the same patient. Nothing is more tiresome than to 

 have to change, each moment, the attachment of the conductors, 



