24k 



in one of tlie galvanometer oiirnits all three of the string images 

 show a deflection. If the sensitivity of the strings is properly regu- 

 lated the string image into the circuit of which the potential 

 diiference is introduced will he detlected by i;' cms and each of the 

 other string images by 1^ — a cms. 



The following case may serve as an example. In the experinieiilai 

 subject Hu the resistances of the body are 



/, = 1200 Ohms 



/, = 1000 „ 



/, = 800 „ 

 from which it follows that the mean resistance is / = 1000 Ohms. 

 Two galvanometer resistances of 4400 and 4000 Ohms are raised 

 by means of rheostats to 15200 Oiims and thus made e(iuai to the 

 third galvanometer resistance. We then get 



q — 6200, a = .V- = 0,08, and E = ö (1 + ^0 = 1,08 cm. 

 2(/ 



The sensitivity of eacii galvanometer must therefore be regulated 

 in such a way that when in one of the circuits one millivolt is 

 introduced, the string image that belongs to that circuit will show 

 a deflection of 10.8 mms. The other string images will be deflected 

 by 0.8 mms. 



The curves obtained in this way show a complete agreement 

 within the limits of observation with ihe formula quote<l. In the 

 measurement of a curve of complicated shape with a strongly negative 

 peak Rin no deviation was found to be larger than 0.1 mm. 



The simultaneous registration of the E. K. G. by three derivations 

 has provided a new and not unwelcome proof of the accuracy with 

 which the string galvanometer is capable of reproducing the potential 

 oscillations of the human heart. Kor the direct practical proof that the 

 formula for the three derivations is right, can only be given, when 

 each of the three curves is accurate in itself. 



It is worth mentioning, that the object can be obtained with the 

 ordinary commercial string galvanometers. Our curves are obtained 

 partly with the original model, partly with the double string-holder 

 of the Cambi'idge model. 



The method here described further opens the possibility of deter- 

 mining the manifest value and the direction of the potential difference 

 in the heart itself, in an easy and certain way. If, in Ihe measure- 

 ments, one is obliged to use curves which have been registered one 

 after the other, one often meets with difficulties. If the curves have 

 a complicated form it is nnl always easy to ascertain the corresponding 



J7 



Proceedings Royal Acad. Amsterdam. Vol. XVUI. 



