PHYSICS: C. BARUS 
331 
attain the completeness of function attained by limbs in the same rela- 
tive positions with the normal limb extirpated. Although such limbs 
may be well suppHed with peripheral nerves, derived from segments of 
the cord posterior to the normal limb level, their greatly impaired move- 
ments appear to be a consequence of their inadequate supply of central 
efferent neurones, which run apparently only as far as the normal 
limb level where they discharge into the somatic motor centers of the 
normal intact limb. 
The generally restricted and non-adaptive movements which these 
limbs do exhibit upon stimulation are probably effected through more 
or less imperfectly connected intraspinal, intersegmental correlation 
neurones of the levels from which peripheral innervation is derived. 
A more complete account of the experiments reported in this paper 
will appear in later publications. 
1 Braus, H., Morph. Jahrb., 35, 1906. 
2 Banchi, A., Anat. Anz., 28, 1906. 
3 Gemelli, F. A., Rev. Pathologia Nervosa Mentale, 11, 1906. 
* Harrison, R. G., /. Exp. ZooL, 4, 1907. 
6 Detwiler, S. R., Ibid., 4, 1918. 
6 Herrick, C. J., /. Comp. New., 24, 1914. 
THE INTERFEROMETRY OF RAPID VIBRATIONS"^ CHIEFLY 
IN RELATION TO TELEPHONE CURRENTS 
By C. Barus 
Department of Physics, Brown University 
Communicated June 13, 1919 
i. Introductory. — The preceding apparatus^ with telescopic or micro- 
scopic enlargement of the telephonic vibrations, behaved on the whole so 
satisfactorily, that it seemed worth while to try a similar design on 
the interferometer. I was inclined to doubt the feasibility of the plan; 
but it appeared on trial that the high tension wires actually keep the 
auxihary mirrors of the interferometer practically quiet; so that in the 
absence of alternating current it is not difficult to find the fringes. 
Tense wires are out of step with the usual laboratory tremors. The 
system needs no special damping. 
The displacement of achromatic fringes due to the induced second- 
ary current is normal to their direction. The objective of the vibra- 
tion telescope is to oscillate in the direction of the fringes and to 
