February 6, 1908J 



NA TURE 



IZZ 



of eight observations, whiih rarely differed among them- 

 selves by more than two or three degrees. 



That portion of the wave-surface which passes the 

 observer at any station was generated at the point where 

 the apparent direction of the sound cuts the line of fire, 

 and since the trace of the wave on the trajectory neces- 

 sarily has the velocity of the projectile at the place where 

 it was formed, and moves along the normal with the 

 ordinary velocity of sound, it is plain that at those points 

 the velocity of the bullet is the velocity of sound -=- the 

 sine of the angle which the tangent to the wave-surface 

 makes with the trajectory. 



The spots, -I-, show the velocities thus computed, and 

 the full curve gives the actual velocity, as determined by 

 firing, at various ranges up to looo yards, into a ballistic 

 pendulum. 



The agreement of the values of the velocities thus 

 obtained with the true velocities shows the degree of 

 - accuracy with which the direction of the sound was 

 estimated. In this case the difference between the true 

 and observed directions was seldom more than a few 

 degrees, and was generallv in one direction. 



k sound which is caused by the detached waves, such 

 as those which accompany a bullet, can scarcely be said 

 to have a pitch, but the wave-length is certainly small 



e arrows show the apparenl 

 to the wave-surface, calcui 

 projectile, obtained from 

 projectile, as deduced froir 



alloy. In the third case, mere traces of the copper and 

 tin were dissolved by the mercury, although each of 

 the constituent metals of the alloy would by itself 

 be readily taken up. .-X solid amalgam was, however, 

 formed. 



These experiments, which were interrupted by illness of 

 the author, go to show that the relations of mercury to 

 alloys are not the same — at any rate for those tried — as to 

 the component metals taken separately. 



December 5, 1907. — " The Reciprocal Innervation of 

 Antagonistic Muscles. Note XI. Further Observations on 

 Successive Induction." Bv Prof. C. S. Sherrington, 

 F.R.S. 



This communication announces that an essential part of 

 the fle.\ion-reflex of the limb is a contraction of the 

 e.vtensor muscles which sets in immediately the external 

 stimulus which excites the reflex is discontinued. The 

 external stimulus, it may be recalled, while exciting the 

 flexor muscles to contraction, produces relaxation of their 

 antagonists, the extensors. This latter it effects by quell- 

 ing (inhibiting) all nervous discharge for the time being in 

 the extensor moto-neurones of the spinal cord. The in- 

 hibition of the moto-neurones is on cessation of the 

 stimulus followed by a superactivity in them accompanied 

 by the discharge of impulses 

 from them into the muscles 

 they innervate, namely, the 

 extensors. This tendency to 

 motor discharge which fol- 

 lows on the inhibition had 

 ,''' been noted in previous com- 



munications by Prof. Sher- 

 rington, but the evidence of 

 it had hitherto been only 

 indirect. It had been found 

 that on withdrawing the in- 

 hibitory stimulus the in- 

 hibited part of the reflex 

 arc showed itself more 

 easily excitable by stimuli 

 than it had been before the 

 inhibition occurred. 



In the present communi- 

 cation it is shown that the 

 inhibited centre actually dis- 

 charges spontaneously on 

 withdrawal of the external 

 inhibitory stimulus that de- 

 presses it. It is further 

 ■jhown that the inhibited 

 : the normals centre will spontaneously 



,rection of the sound at the stations ABC... The dotted I _._ 



d from the known velocity of the projectile. The full curve is the velocity of the discharge even in face of a 

 perimentswith the ballistic pendulum. The spots, -|-, are the vek cities of the weak inhibitorv stimulus if 



the observed d: 



of the i 



compared with the distance between the ears, and is, 

 indeed, comparable with the dimensions of the bullet itself. 

 It would seem, therefore, that the ears can determine 

 the direction of a sound, not only by difference of phase, 

 but by the actual difference in the times at which a single 

 pulse reaches them. 



" Results of the Interaction of Mercury with .\llovs of 

 other Metals." By Dr. J. W. Mallet, F.R.S. 



It being well known that alloying metals with each other 

 often modifies notably their relations to acids and other 

 non-metallic reagents, it seemed desirable to ascertain 

 what the behaviour would be of solid alloys to licjuid 

 metallic mercury. 



In the experiments reported in this paper three alloys 

 were used, namely, tin-platinum, silver-platinum, and 

 copper-tin, approxiinately PtSn,, PtAg,, and SnCu,. 

 These were shaken up in a finely divided state with pure 

 k mercury in large excess. In the first case the tin was 

 completely protected by the platinum from amalgamation, 

 and neither of the solid metals was dissolved by the 

 mercury. In the second case the presence of the silver 

 brought about amalgamation of the platinum, which would 

 not have been so affected if alone, and both metals were 

 dissolved by the mercury, the platinum, however, in less 

 proportion than that in which it was present in the solid 



NO. 1997, ^O^- 77] 



that stimulus follows on a 

 strong inhibitory one. The 

 process in virtue of which inhibition of the arc Leads 

 to or induces a subsequent superactivity of the arc 

 is called successive induction, because of its analogy to 

 certain processes in the physiology of vision which an 

 also called inductive. The intensity of the successive in- 

 duction increases with increase of the intensity of the 

 inhibitory stimulus and with increase — up to certain limits 

 — of the duration of the inhibitory stimulus. In other 

 words, the stronger and longer the inhibitory stimulus, 

 the greater the contraction which ensues on the withdrawal 

 of the stimulus. 



The contraction of the extensors of the limb which thus 

 follows on their relaxation by reflex inhibition is probably 

 an important, perhaps the most important, fac-tor in the 

 extension phase of the reflex stepping of the limb. Its 

 occurrence supplies an explanation for the relatively poor 

 representation of extension as a primary movement in the 

 motor area of the cortex cerebri. It may be fundamentally 

 analogous to the excitation which occurs in a peripheral 

 nerve at the site of the anode of a voltaic current when 

 the passage of the current is broken. It is, at any rate, 

 perhaps the most striking instance known of a depression 

 which in .-Xmim v. Tschermak's terms is allonomic, being 

 followed by a reverse condition the process of which is 

 autonomic. In other words, an allonomic depression 



