A. M. Mayer—Method of Detecting the Phases, etc. 387 
Art. XLV.—On a method of detecting the phases of vibration in 
) the air surrounding a sounding body; and thereby measuring 
| directly in the vibrating air the length of its waves and exploring 
| the form of its wave-surjace ; by ALFRED M. Mayer, Ph.D., 
Member of the National Academy of Sciences. Professor of 
Physics in the Stevens Institute of Technology. 
THE curve A, B*, B4 ete., is the well known symbolic repre- 
sentation of the dynamic condition of the air, at a given instant, 
when traversed by simple sonorous vibratiohs. Those portions 
of the curve above the axis OX represent the length and manner 
A BI B? B3 Bi B BE 
of the aerial condensations, while those flexures below the axis 
represent the rarefactions; therefore similar points of the flex- 
ures above the axis, or sim ints in the flexures below the 
axis, represent like phases of vibratory motion. Imagine these 
Conditions of the air produced by a vibrating at A; then 
tances from A, equal to any number of whole wave-lengths the 
B will, at the same moment of time, swing with A, but 
A; while at intermediate positions, on the line OX, the 
oscillations of B will be lagging somewhat behind or be slightly 
mm advance of the phase of A’s vibration. 
After this it is evident that if, by any means, we can see af. 
the same time the vibrations of A 8g of B, we will (if the 
received conception of the nature of a vibration’s propagation 
1S Correct) see their motions just as has been described above, 
and will therefore be able to measure, directly in the air, a wave- 
h and to determine any wave surface enclosing a vibrating 
y- I have devised several processes. I will, however, here 
