242 
this, with very simple means, the patient: 
daily recovered her health. There is every 
reason to believe that many of the stomach 
complaints, which baffle the best medical 
advice, owe their origin to animalcule 
taken into the stomach, either in the state 
of ova or larva, in the ‘interstices of fruits 
and vegetables, and in river or pond 
water. To give our readers any caution 
respecting eating fruits, we are well aware 
would be an useless task: but as it is pro- 
bable that much greater mischief arises 
from the use of impure water, we strongly 
recommend all those who are obliged to 
use pond or river water (particularly at 
this season of the year, and after an unu- 
sually hot summer) to boil it in every case 
before use, as the only mode of destroying 
the animalcule. Though it is now common 
to filter such water, yet the ova of 
many insects are so exceedingly minute as 
to pass through.any filter without injury, 
and on being taken into the alimentary 
passages, are, in fact, placed ina hot bed, 
where they soon become larva of large 
size, and often occasion great suffering to 
the unfortunate patient. 
Lightning Rods.—For a tower, the stem, 
being that part which rises above the build- 
ing, should be from fifteen to twenty-five 
feet above the roof, according to the area 
of the building: the domes and steeples of 
churches, being usually much higher than 
the surrounding objects, do not require so 
high a conductor as buildings with exten- 
sive flat roofs: for such, therefore, it will 
be sufficient that the stem rises six or eight 
feet above the weathercock ; and being light, 
it may easily be fixed without obstructing 
the motion of the vane. 
For .a powder-mill, it must be fixed 
with the utmost care and precision; and 
should not be placed on the buildings, but 
on poles, purposely erected at eight or ten 
feet distance. The stem should be séyen 
or nine feet long, and the poles of such a 
height as to raise them fifteen or twenty 
feet above the building. It is advisable 
to have several rods around a magazine ; 
which, however, if a tower or lofty building, 
may be thought sufficiently defended by a 
double-copper conductor without stem. But 
as the influence of such conductor will not 
extend beyond the building to which it is 
annexed, it cannot attract the lightning 
from any distant object. 
The stem of a lightning-rod for ships 
consists merely of a copper point, screwed 
into a round iron-rod, entering the extre- 
mity of the top-gallant mast. An iron bar, 
connected with the foot of the rod, de- 
scends down the pole, and is terminated 
by a crook or ring, to which the conductor 
is attached ; which, in this case, is formed 
of a metallic rope (the use of which is gene- 
rally recommended, because of the brittle- 
ness-and consequent difficulty of bending 
rod-conductors), connected’at its lower ex- 
Spirit of Philosophical Discovery. 
, defects, and of sufficient size. 
{[Oct. 1, 
tremity with a bar, or plate of metal, at- 
tached to the sheathing of the yessel. 
Small vessels require but one; large ships 
should have one on the mizen, ” and another 
on the main-mast. It has been proposed 
to have conductors fixed to the surfaces of 
masts, and the electric fluid conveyed by 
mean of strips of metal, over the deck and 
sides of the vessel. But this mode is highly 
objectionable ; and perhaps the best me- 
thod that has yet been devised, is to con- 
vey the electric fluid immediately to the 
water, by a series of long copper links. A 
few months ago, a vessel with powder on 
board was struck by lightning and blown 
up; the conductor, at the time, not reach- 
ing the water, for being loose, it had been 
drawn upon deck. It is allowed, from ex- 
periment, that the stem of a lightning-rod 
is an effectual preserver to the circle of 
which it is the centre, and whose radius is 
twice the height of the stem: by this rule, 
a building, sixty-feet square, requires a 
stem raised fifteen or eighteen feet in the 
middle of the roof; and a building, 120 feet 
square, requires a stem of thirty-feet, and 
such is often used; but it is better, instead 
of one stem of that height, to have two 
half so high ; one thirty feet from one end 
of the building, the other alike distance 
from the other end, and consequently the 
two at sixty feet distance from one another : 
and this rule ghould be followed either in 
larger or smaller buildings. 
Flint Glass. —Opticians and astronomers 
have long lamented the imperfection of re- 
fracting telescopes, from the impossibility 
of obtaining flint glass for lenses perfectly 
homogeneous, without striz or any other 
These dith- 
culties. have been at length removed, by 
the invention of M. Guinand, an ingenious 
self-taught artist of Brenets, in the canton 
of Neufchatel, Switzerland. In his youth 
he assisted his father as jomer, and at the 
age of thirteen became a cabinet-meker. 
Having seen an English reflecting telescope, 
he procured leave to take it to pieces, and 
put it together again. This gave the first 
impulse to the pursuit of that object, which 
afterwards gained him so much celebrity, 
When he attempted to manufacture achro- 
matic glasses, meeting the same difficulties 
which others had experienced, he began (at 
the age of thirty-five) to make experiments 
on the manufacture of glass. With no ad- 
vantages except those which his own inge- 
nuity supplied, he erected a furnace with 
his own hands, and continued, for many 
years, a series of expensive and fruitless 
experiments, labouring occasionally at some 
mechanical employment to earn the means 
of subsistence and of purchasing wood, 
and the necessary materials for his furnace, 
his crucibles, and his glass. 
that he might be able to repeat any success- 
ful experiment. At length he gbtained 
blocks: 
He carefully 
noted the particulars of every operation,’ 
