: TRANSACTIONS OF SECTION G. 957 
"flow of magnetic force transversely is therefore that which effects the attraction of 
the strip, and may be represented as a series of magnetic stitches passing to and fro 
between the two sets of rails and the strip. 
j 
3. Alternating versus Continuous Currents in relation to the Human Body. 
By H. Newman Lawrence, M.[.H.E., and Arron Harriss, M.D. 
This paper is based upon experiments made with dynamo-generated currents, 
both continuous and alternating, and with the skin of the subjects in its normal, 
-unmoistened state. The matter is considered under the following heads, viz.:— 
Resistance, including variations due to change in contact-area; and Sensations, 
_ including initial shock and continued contact. 
Resistance was measured by connecting two or more persons to a dynamo 
circuit at an E.M.F. of about 100 volts, noting the current-strength passed, and 
then calculating therefrom the resultant resistance of each person. The tables 
given show an average resistance to continuous current of 6,185 Ohms, and to 
alternating current of 4,008 Ohms—.e., about 1°5 higher for continuous current than 
ifor alternating. Experiments made regarding contact-area showed that it is an 
important factor ‘ in determining the seriousness or slightness of accidents in light 
wand power circuits.’ 
Sensation was tested by passing currents from the same dynamos, using resist- 
rance-coils to reduce the current to a convenient level, Two distinct points of 
comparison were taken, one called ‘ Discomfort Point,’ and the other ‘ Fixation 
Point.’ The tabulated results show that discomfort point was reached with an 
average of 18-7 milliampéres of continuous current, and with 3°9 milliampéres of 
alternating current. This indicates that sensation to alternating current is 4°7 
times greater than it is to continuous current. 
With continuous current, ‘in each instance burning sensation under the elec- 
trodes became unbearable after about thirty seconds ; this was the only objection- 
able feature, though electrolytic action was sufficiently marked to induce slight 
blistering in two of the cases.’ 
With alternating currents, a tingling sensation was felt, rapidly increasing to 
muscular contraction, becoming more and more unpleasant, and accompanied by a 
feeling of heat in the neighbourhood of the electrodes, though not immediately 
under the site of contact, as in the case of the continuous current. 
The average fixation point to alternating current was 7'5 milliampéres; but 
no such point could be found with the continuous current, thus emphasising this 
important difference between the two forms of current as regards danger likely 
to result from accidental contact. 
Initial shock is defined as that in which the time-period of contact was a 
minimum. Many subjects were tested, who one and all considered the initial 
_ shock of continuous current to be far less unpleasant than that of alternating cur- 
rent when equal current-strength was used; but ‘this, from the nature of the 
; experiment, can only be tested with small currents, and it is conceivable that with 
_ larger currents such marked differences may not be observable.’ 
< In continued contact with the continuous current ‘we have no muscular fixa- 
: fttion, and the subject of the accident would be able to release himself.’ On the 
_ other hand, with alternating current ‘the subject would be absolutely fixed in setw 
until released by extraneous aid, being exposed the whole time to the full effect 
_ of the current passing.’ 
In drawing the following conclusions, the authors say: ‘We desire to call 
_ attention to the fact that they are based upon certain conditions, and, while we 
" helieve them to be sufficiently accurate and reliable under these conditions, we in 
mo sense claim them as true under all conditions.’ 
‘ CoNCcLUSIONS. 
_ £(a.) That when the human body, with the skin in its normal, unmoistened con- 
_ dition, comes into contact for an appreciable time with bare-metal conductors of a 
E ‘ 
ale 
