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plans of all details I have ready to describe when wanted, and shall 

 very soon be able to state exactly the battery power required for a 

 cable of stated dimensions. 



2. Plan of observation for receiving a message. The instrument 

 which I propose is Helmholtz's galvanometer, with or without modi- 

 fication. The time of vibration of the suspended magnet, and the 

 efficiency of the copper damper, will be so arranged, that during the 

 electric pulse the suspended magnet will turn from its position of 

 equilibrium into a position of maximum deflection, and will fall back 

 to rest in its position of equilibrium. The possibility of fulfilling 

 these conditions is obvious from the form of the curve I have found 

 to represent the electric pulse. The observer will watch through a 

 telescope the image of a scale reflected from the polished side of the 

 magnet, or from a small mirror carried by the magnet, and he will 

 note the letter or number which each maximum deflection brings into 

 the middle of his field of view. 



3. Code of letter-signals. The most obvious way of completing 

 a telegraphic system on the plans which have been described, is to 

 have the twenty-six letters of the alphabet written on the scale of 

 which the image in the suspended mirror is observed, and to arrange 

 thirteen positive and thirteen negative strengths of electric operation, 

 which will give deflections, positive or negative, bringing one or other 

 of these letters on the reflected scale into the centre of the field of 

 view. But it would be bad economy to give the simple signals to 

 rare letters, and to require double or triple signals for double and 

 triple combinations of frequent occurrence. Besides, by the plans 

 which I have formed, it will, I believe, be easy to make much more 

 than thirteen different positive and thirteen different negative 

 strengths of electric operation, giving unmistakeably different degrees 

 of deflection; and if so, then many of the most frequent double and triple 

 combinations, as well as all the twenty-six letters of the alphabet 

 singly, might be made by simple signals. But it is also possible 

 (although I believe highly improbable), that in practice only three 

 or four, or some number less than thirteen, of unmistakeably different 

 deflections could be produced in the galvanometer at one end by 

 electric operations performed on the other extremity. If so, the 

 whole twenty-six letters could not each have a simple signal, and 

 double signals would have to be chosen for the less frequent letters. 



