THE YOUNG SCIENTIST. 
106 
the less potash it will bear. In fact, 
tender bones should be bleached without 
this agent. 
Observatory on Mount Etna. 
THE following* forms part of an ac- 
count of this observatory, given by 
Signor Tedeschi : The observatory is built 
on a little eminence, on the side of the 
central crater of Etna, a position which 
makes it almost certain that should a 
stream of lava issue on that side, it would 
divide into two streams, and flow harm- 
lessly on each side of the little hill. The 
building consists of two stories, the joint 
height of which is nine metres, and the 
base of the edifice occupies a superficial 
area of 200 square metres. In each story 
there is a circular room surrounded by 
other chambers destined for different 
uses. In the centre of the circular room 
in the lower story there is a solid pillar to 
support the great refractors. All the in- 
struments, as well as a fine collection of 
seismographic and meteorological appa- 
ratus, are in the upper story, in the large 
circular room of which are the telescope 
and chronometrical apparatus. This 
room is roofed with a movable iron cu- 
pola. In this story are also the rooms 
for foreign visitors, and a little terrace, 
from which there is a view of half Sicily, 
Malta, the Lipari islands, and part of 
Calabria. The observatory on Etna is 
the highest building in Europe. The ob- 
servatory on Vesuvius is 619 metres above 
the level of the sea, the Hospice of the 
Gotthardt, 2,075 metres, and that of St. 
Bernard 2,491 ; while the Etna observa- 
tory is at the height of 2,942 metres. At 
this great elevation there is no fear, in 
taking astronomical and spectroscopic 
observations, of the perturbations pro- 
ceeding from the variable density of the 
different atmospheric strata, so that this 
observatory will probably render invalu- 
able service to astronomical science and 
terrestrial physics. 
Sound. 
The following curious observations of sound 
have been carefully verified by an extended 
series of experiments: The whistle of a loco- 
motive is heard 3,300 yards ; the noise of a rail- 
road train, 2,800 ; the report of a musket and the 
bark of a dog, 1,800 ; an orchestra or the roll of 
a drum, 1,600; the human voice reaches to a 
distance of 1,000; the croaking of frogs, 900; 
the chirping of crickets, 800. Distinct speaking 
is heard in the air from below up to a distance 
of 600 yards ; from above, it is only understood 
to a range of 100 yards downwards. It has been 
ascertained that an echo is well reflected from 
the surface of smooth water only when the 
voice comes from an elevation. Other similar i 
phenomena connected with the transmission of i 
sound have been observed, but the results dis- 
agree, either from inaccuracy in the observa- 
tions or from the varying nature of the circum- 
stances affecting the numbers obtained. Such 
variations occur to an extent of 10 to 20 per i 
cent., and even more. The weather being cold 1 
and dry, or warm and wet, are the chief influ- 
encing causes. In the first case the sound goes 
to a greater, and in the second to a lesser dis- 
tance. 
Seeing and Signaling. 
M. Charpentier tells us that the time elapsing 
between a person seeing a signal and being able 
to repeat it with his forefinger is about thirteen- 
hundredths of a second. With some people the 
interval is twice as long, but the above may be 
taken as the average. M. Charpentier terms 
the interval in question the " duration of lumin- 
ous perception," and he measures it in a very 
ingenious manner. A black disk is set revolv- 
ing at a given speed, and the observer faces it, 
having under his finger an electric key. There 
is a small opening or window in one part of the 
disk, and when this comes round opposite the 
observer he sees a light shining through it. 
Immediately he presses the key and an electric 
signal passes to the revolving disk. The disk 
is stopped, and the distance between the window 
and the record of the signal being measured 
furnishes the result. The distance between the 
two points on the disk is, of course, easily 
turned into time, since the disk was revolving 
at a known speed. 
Minute Workmanship. 
The Salem Museum, Massachusetts, has in 
its possession a cherry stone containing one 
dozen spoons. The stone is of the ordinary 
size, the spoons being so small that their shape 
and finish can be distinguished only by the mi- 
croscope. This is the result of immense, labor 
for no decided 13^ use'ul purpose, and there are 
numbers of other objects in existence the value 
of which may be said to be quite as indifferent. 
Thus, Dr. Oliver gives an account of a cherry 
stone on which were carved one hundred and 
twenty-four heads so distinctly that the naked 
eye could distinguish those belonging to popes 
and kings by their mitres and crowns. A Nu- 
remberg top maker inclosed in a cherry stone 
which was exhibited at the French Crystal 
Palace, a plan of Sebastopol, a railway station, 
and the " Messiah " of Klopstock. Pliny, too, 
mentions the fact that Homer's Iliad, with its 
15,000 verses, was written in so small a space as 
to be contained in a nutshell. The greatest 
