2 Trans. Acad. Sci. of St. Louis. 
occur in a revolution, the balancing knob was displaced 
along the shaft. This results in another unbalanced mo- 
ment which must be carried by the pivots on which the 
shaft is mounted. It was estimated that the pivots would 
at 800 revolutions per second, have carried lateral revolv- 
ing thrusts amounting to 75 or 80 pounds. It was there- 
fore determined to repeat this work. Through the cour- 
tesy of the Department of Physics of the University of 
Chicago the construction of a rotating mirror was se- 
cured from patterns used in the building of a mirror for 
that department. A mile of wire was contributed by the 
Kinloch Telephone Company of St. Louis, and Wheat- 
stone’s line was reproduced in the hallway of Eads Hall 
at Washington University. The reflected images of the 
sparks on the spark board were thrown into a large copy- 
ing camera. Datum sparks when the mirror was at rest 
could thus be obtained, and the sparks produced during 
rotation could also be obtained. When both terminals of 
“ESt' to tiie Miacwuiue UCTCULTCU UTSt; THOS THU ppars pou- 
ond, and the spark nearest to the ground occurred last. 
The sparks came at regular time intervals. Wheatstone’s 
conclusion was therefore verified.” 
The question then arises, are these disturbances dis- 
charges of the positive and negative fluids, or are they 
disturbances in the nature of compression and rarefac- 
tion waves in a fluid? Wheatstone’s result does not de- 
cide between these two possible hypotheses. Rowland’s 
2 Probably Wheatstone’s drawings represent apparatus used in pre- 
liminary work, and not the apparatus which he finally used for obtaining 
his published results. 
