64 Dr. A. D. Waller. Various Inclinations of the 



clearly the theoretical values of the differences in the several inferior 

 leads — axial and right lateral, equatorial and left lateral — which in fig. 5a 

 were assumed to be identical under the designations right inferior and left 

 inferior on the assumption that the two feet might be regarded as isoelectric* 

 By reference to this figure it is easy to satisfy himself what order of error 

 can arise by regarding the two feet as isoelectric, and to understand without 

 effort certain minor but otherwise puzzling discrepancies met with in certain 

 hearts when the several inferior leads are compared by means of a highly 

 sensitive instrument. Thus e.g. it is obvious at a glance that such dis- 

 crepancies become more sensible in " horizontal " than in " vertical " cases, 

 and that e.g. a 64° heart offers the paradoxical instance of a positive left 

 lateral and a negative equatorial spike. And the observation which I have 

 frequently made without thoroughly understanding it to the effect that an 

 equatorial spike is smaller than the left lateral when positive, but the larger 

 of the two when negative, is rendered obviously intelligible. Likewise that 

 mentioned without comment in Part I, p. 510, of this paper that the left is 

 slightly larger than the right longitudinal spike.f 



The two experiments described above can be repeated with advantage 

 in view of this second diagram model, upon consideration of which 

 it will be apparent that in repeating Experiment 1 the left lateral is 

 slightly more favourable than the equatorial lead, and that in repeating 

 Experiment 2 the equatorial is slightly more favourable than the left 

 lateral. 



The differences of value between axial and right lateral and between 

 equatorial and left lateral are obviously small, and their absolute measure- 

 ment involves a large relative error. Tor instance, in the case of J. C. W. the 

 values come out as follows : — 



* In my first communication (' Phil. Trans.,' 1889, p. 191) the two feet are given as 

 being isoelectric, although I was well aware of the fact that theoretically there should be 

 a slight P.D. between them. 



t In that connection, speaking only of the four leads between the mouth and four 

 extremities, I used the expression right and left superior and inferior, whereas for right 

 and left inferior I should have used the designations right and left longitudinal, in 

 accordance with the terminology of the present paper, where right and left inferior refer 

 to hands and feet. The table given on p. 510 should read accordingly : — 



Eight superior ... 



Left superior 



Right longitudinal 

 Left longitudinal . 



3 (= 0-00023 volt) 



15- 3 '(= 0-00118 „ ) 



16- 5 (= 0-00126 „ ) 



17- 5 (= 0-00135 „ ) 



