SCIENTIFIC SUMMARY. 
441 
Titanic acid .... 
. 52*74 
Iron peroxide .... 
. 42-29 
Alumina 
. Trace 
Lime and magnesia 
. 4-28 
Loss by ignition .... 
. 0-70 
100-01 
The mineral is dimorphous with menaccanite or ilmenite. The crystalline 
form, habit, and the physical, and in certain respects also the chemical, pro- 
perties of the mineral are those of brookite ; but closer examination shows it 
not to be that mineral. Szaboite is a triclinic mineral, which closely re- 
sembles pyroxene in appearance. It is composed of : — 
Silicic acid .... 
. 52-35 
Iron peroxide 
. 44-70 
Alumina .... 
. . Trace 
Lime and magnesia 
. 3-12 
Loss by ignition . 
. 0-40 
100-57 
Chemical constitution and crystalline form at first sight recall babingtonite, 
but the resemblance is not supported by further investigation — Miner alogische 
und Petrographische Mittheilungen , 1878, i. 77. 
PHYSICS. 
Acoustic Repulsion . — It can be shown theoretically that the average 
pressure at the node in a column of air vibrating in stationary waves cannot 
be equal to zero as long as the amplitude of vibration is not infinitely small. 
M. Dvorak has made experiments in illustration of this fact. In a resonator 
open at one end, there is a node at the other. In the inside, near the closed 
end, there is greater pressure than outside. When such resonators are deli- 
cately suspended, and turned towards the source of sound, or the resonant 
box of a tuning-fork, the repulsion is so great that it is apparent even with 
an ordinary brass Helmholtz resonator, weighing with its counterpoise 142 
grammes. 
An “ Acoustic Mill,” showing continuous rotation, was made by fastening 
from very light paper, or thin glass, resonators on the arms of a light wooden 
cross, balanced on a glass cap, with their openings facing the same way 
towards the source of sound. Rapid rotation is obtained by using a large 
Knadt’s tube as the source. If a cone of stiff paper be held with its large 
extremity towards the sounding body, and of such a size that it vibrates to 
the same note, on excitation, a current of air rushes from the smaller end 
with such violence as to be felt and heard, and to blow cut a candle at the 
distance of 20 centimetres. It appears that these experiments had been 
independently made, and indeed anticipated, by Professor A. M. Mayer, ot 
New York. 
