413 
Natural PMlosophy^Acoustics — Galvanism, 
September, and the daily change is a maximum about S o’- 
clock in the afternoon. The greatest magnitude of the diur- 
nal deviation does not exceed 20 minutes in ordinary circum- 
stances. 
ACOUSTICS. 
6. Subterraneous Sounds in Granite Rocks.^M., Humboldt 
was informed by most credible witnesses, that subterraneous 
sounds, like those of an organ, are heard towards sunrise, by those 
who sleep upon the granite rocks on the banks of the Oroonoko. 
He supposes them to a,ris(e from the difference of temperature 
between the external air and the air in the narrow and deep cre- 
vices of the shelves of rocks. During the day, these crevices are 
heated to 48^ or 50®. 1’he temperature of their surface was of- 
ten 39®, when that of the air was only 28®. Now, as this diffe- 
rence of temperature will be a maximum about sunrise, the cur- 
rent of air issuing from the crevices will produce sounds which 
may be modified by its impulse against the elastic films of mica 
that may project into the crevices. Messrs Jomard, Jollois and 
Devilliers heard, at sunrise, in a monument of granite, placed at 
the centre of the spot on which the Palace of Karnak stands, a 
noise resembling that of a string breaking. — Humboldt’s Person-^ 
al Narrative, vol. iv. 
GALVANISM. 
7. Improvement upon the dry Pile of Zamhmi, — In construct- 
ing the dry galvanic pile of Zamboni with tinned paper and 
black oxide of manganese, M. Zamboni recommends the use of 
tinned paper, which, when disposed alone in the pile, has the 
same polarity as when it is employed along with oxide of 
manganese. The reason of this is, that a pile of tinned paper 
has electrical poles. But, whatever be the kind of paper 
which is used, the pile always increases in energy, and its 
polarity always coincides with that of a pile of tinned paper and 
oxide of manganese, when the paper has been impregnated with 
.a solution of sulphate of zinc, and afterwards dried. In pre- 
paring the paper M. Zamboni avails himself of a dry season. 
He spreads the solution of sulphate of zinc over the face of the 
VOL. I. NO. 2. OCTOBER 1819. E 6 
