Physics. 823 
sound is situated below the plane of best hearing, and that we 
should be able by sinking the head to bring the source of sound into 
the line of sight in the manner just described for a sound above 
the head. 
measuring altitude and azimuth) we have two separate motions 
noticed on page 321 of vol. xvi, III, of this Journal. Into the 
Space above the mercury of one barometer-tube chloral- hydrate 
was evaporated, while ie similar space of a second tube was filled 
oryatallized — mess a was then introduced. Very soon a 
depression of the mercury column indicated that the water of 
1, te mrp of the salt had evaporated into the dry vapor of 
chloroform, while the constancy of level in the first tube showed 
T 
exceptions to a law so well established as that of the equality o 
molecular volumes in the aériform state ought always to be very 
closely serutinized. 
