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resistance of a thin, silvei-etl (|iiai-lz liiread. Of tlie formerly mentioned 

 qnartz threads 10, J 3 and 14, thread J 3 will give the best results 

 in tracing the electrocardiogram, since of this thread the ohmic 

 resistance is smallest. To be sure, the normal sensitiveness of thread 

 14 is abont 1.4 times greater, but the currents, received by this 

 thread from the pulsating heart, will be about twice weaker on 

 account of the greater resistance. 



Besides having a smaller ohmic resistance thread 13 has over 

 thread 10 the additional advantage of possessing a smaller air-resistance 

 to its motion. This latter property here plays an important part. 

 For in order to obtain deflections of practicable magnitude, e.g. of 

 10 to 15 mm., the sensitiveness of the galvanometer must be so 

 adjusted that a potential difference of 10—* volt in the circuit corre- 

 sponds to 1 mm. ordinate. For obtaining this the quartz thread must 

 be rather feebly stretched, so that the deflections are aperiodic and 

 under these circumstances a diminution of the resistance to the motion 

 of the string will cause a quicker deflection. 



Sticking to the condition that a potential difference of lO-'* volt 

 shall correspond to 1 mm. ordinate, we trace with string 13 a human 

 electrocardiogram which is almost absolutely accurate. 



With string 10 and especially wath sti-ing 14, however, curves 

 are then recorded Avhich require corrections. Although the amounts 

 of these corrections are small, and do not go beyond a whole milli- 

 metre, so that in many cases they may be )ieglected, it is not 

 superfluous briefly to remember here the cause of these deviations. 

 It is found in the relation between the velocity of the deflection of 

 the galvanometer and the velocity of the oscillations in potential 

 caused by the action of the heart. 



The quicker the galvanometer deflects, the more accurate the 

 photogram of the oscillation of potential will be. 



The sensitiveness of string 14 must be so adjusted for tracing the 

 human electrocardiogram that about 1 mm. ordinate corresponds to 

 0.5 X 10-s amp. Now with this quartz thread the limit of aperiodicity 

 is in a circuit with small external resistance only reached with an 

 about four times greater tension of the string. If by applying a 

 vacuum the resistance to the motion of the string could be diminished 

 so that the limit of aperiodicity were already reached at the first 

 mentioned sensitivejiess, when tracing the electrocardiogram the 

 velocity of motion of the string would be considerably increased, 

 so that then also string 14 might reproduce the oscillations of poten- 

 tial with almost absolute accuracy. 



We now pass to the discussion of a second example from electro- 



