1881.] On the Tendinous Intersection of the Digastric. 



20 



the permanent twist becomes greater and more difficult to reduce 

 to zero. 



If a wire which has internal strains is heated to redness, these 

 strains almost entirely disappear, and I can thus reduce by heat a 

 strain which a current had produced, but heat, whilst allowing of 

 greater freedom and motion of its molecules, does not prevent an 

 internal strain being set up, for whilst heat can reduce the wire to 

 zero, after the passage of the current, the effects are increased. If, 

 during the time that the wire is at a red heat, the current is passed 

 in the same time, and at the same instant we take off the current and 

 the external heat, the wire when cold will be found to have a higher 

 degree of strain than previously possible with the wire when cold. 



We have seen that both mechanical vibrations and heat can reduce 

 the wire to a zero, but its action is very slow, several minutes being 

 required ; but the action of electricity in producing a permanent twist 

 is exceedingly quick. I have found that a single contact, whose dura- 

 tion was not more than 0"01 of a second, was equal to that of a 

 prolonged contact of several minutes, and magnetism was equally as 

 quick in reducing this strain to zero. And it is the more remarkable 

 when we consider the very great mechanical force required by torsion 

 of the wire to untwist the strain produced in an instant of time by 

 electricity. 



The results I have given are those obtained upon soft iron wires of 

 \ millim., but I have experimented with different sizes up to 3 millims. 

 diameter. The results with 1 millim. diameter were quite as evident 

 as the \ millim., but on the 3 millim. wire the strain was reduced 

 to 25° instead of 50°, owing to the extreme rapidity and low electrical 

 resistance compared with my small battery wires. On a telegraph 

 line, the wire of which is almost entirely of iron, there must be a very 

 great strain set up, which, however, would remain a constant, except 

 where reversed currents are used, and in this case a constant move- 

 ment of the molecules of the wire must be the result. 



I believe it to be most important that we should determine, as far 

 as we can by experimental research, the nature of all molecular 

 changes produced by electricity and magnetism, and in this belief 

 1 am happy in being able to bring this paper before the Royal 

 Society. 



HE. " On the Tendinous Intersection of the Digastric." By G. 

 E. DOBSON, M.A., M.B. Communicated by Professor J. D. 

 Macdonald, M.D., F.R.S. Received March 14, 1881. 



The digastric muscle in man and in many other mammals consists 

 as is well known, of an anterior and a posterior portion, united by a 



