58 E.. W. Blake, Jr.—Articulate Vibrations. 
the plates must be quite long when ar velocity is great. I 
employ plates two feet in length, and that velocities from 
6 to 40 inches per second give good secs The action of 
the light is however inversely as the velocity. To compensate 
for this, the size of the circular opening admitting the light 
may be increased, This, of course, causes an enlargement of the 
luminous image, and apparently involves an injurious widening 
of the line traced, but, as observed by Dr. Stein in his experi- 
ments, the effect of velocity i is to narrow the line pho 
since the maximum exposure is in that diameter of the circular 
poesee which lies in the line of motion. This isa great advan- 
tage, since a variation of velocity in the vibration is marked 
by the widening of the line, often more clearly than by the 
form of the curve. 
I have employed the ordinary photographic process, not at- 
tempting to obtain special sensitiveness. The brightest sunlight 
is required, a slight haziness interfering seavialy with the 
result. y heliostat employs two reflectors of ordinary look- 
ing-glass, and the loss of light is considerable. 
To guide those who may wish to try this method I add the 
ollowing measurements : 
Diameter of circular opening --_-._.-_--- 7s inches.* 
Distance of mirror from circular opening ---. -. -28 feet. 
Distance of mirror pe photographic plate - . _114 inches. 
Bock temas OF tenn 94 inches. 
Size of steel sik i ge, Pic ay pce aed 0° pone 34 inches. 
Weight of steel mirror_-_-_.__. 065 
The question naturally arises whether the mirror may not 
so interfere with the vibrating disc as to destroy its articulation. 
The telephone gives a direct answer and banishes the doubt. 
mirror was attached in the manner already described to 
the dise of a telephone, and the instrument showed itself still 
perfectly capable of eens. and ‘receiving,’ without notice- 
able one of clearness or 
the audible peed of speech traceable in these 
résonie? in other words, is the record com pet I am not 
prepalot = yet to answer this question definitely, but the fol- 
owing experiment leads me to doubt whether an affirmative 
taken from it while the instrument was talking au : 
resulting record was almost a smooth line, poms but very 
slight indications of oaths of the mirror. It would there- 
fore, appear that there are distinctly audible Marae: which 
© Doxending oo talosity toquiveli auc cd. | the light. 
attached to the disc of a receiving telephone and a ‘pho Se © 
ibly. The 
