EAllTlI BREAD. 
787 
ihe upright posture, the less will the motion he, either way. If the 
tube is placed horizontally on a glass plane, the fragment, for instance 
of coach-window glass, instead of moving towards the fire, will 
move from it, and about its axis, in a contrary direction to what it had 
done before ; nay, it will recede from the fire, and move a little up*- 
W'ard, when the place inclines towards the fire. These experiments 
are recorded in the Philos. Trans. No. 476. They succeeded best 
with tubes about twenty or twenty two inches long, which had in 
each end a pretty strong pin fixed in cork for an axis. The causes 
of this phenomenon have not yet been discovered. 
4. Glass is less dilatable by heat than metalline substances, and solid 
glass sticks are less dilatable than tubes. This was first discovered by 
Colonel Roy, in making experiments to reduce barometers to a greater 
degree of exactness than has hitherto been found practicable ; and 
since his experiments were made, one of the tubes, eighteen inches 
long, being compared with a solid glass rod of the same length, the 
former was found by a pyrometer to expand four times as much as the 
other, in a heat approaching to that of boiling oil. On account of 
the quality which glass has of expanding less than metal, M. de Luc 
recommends it to be used in pendulums ; and he says, that its expan- 
sions are always equable, and proportioned to the degrees of heat— a 
quality which is not to be found in any other substance yet known. 
Glass is also more fit, from the condensation of vapours, than metallic 
substances. An open glass filled with water, in summer, will gather 
dew on the outside, just as far as the water in the inside reaches ; 
and a person’s breath blown on it, manifestly moistens it. Glass also 
becomes moist with dew, when metals do not. A drinking glass, partly 
filled with water, and rubbed on the brim with a wet finger, yields 
musical notes, higher or lower as the glass is more or less full, and 
makes the liquor leap. Glass is possessed of very great electrical 
virtues* 
Earth Bread. 
In the German Ephemerides for 1764, we have the following 
account of a kind of bread made of earth. In the lordship of Moscow, 
in the Upper Lusatia, a sort of white earth is found, of which the 
poor, urged by the calamities of the wars which raged in those parts, 
make bread. It is taken out of a hill where they formerly worked 
for saltpetre. When the sun has somewhat warmed this earth, it cracks, 
and several small white globules proceed from it, resembling meal ; 
it does not ferment alone, but only when mixed with meal. M. Sar- 
litz, a Saxon gentleman, informed us, that he had seen persons who 
in a great measure lived upon it for some time. He assures us that 
he procured bread to be made of this earth alone, and of different 
mixtures of earth and meals, and that he even kept some of this 
bread by him upwards of six years ; he further says, a Spaniard 
told him, that this earth is also found in Gerone in Catalonia. It 
would appear from hence, that we are not yet fully acquainted with 
all the modes which nutrition can assume ; and it would be remarka-i 
ble if the curse of war should lead men to provide against the horrors 
of famine. 
