CORRECTIONS i 
and that diamond was a compound of the 
carbonaceous principle and oxygen; that 
he had succeeded in obtaining tlie metallic 
base of ammonia, which, when combined . 
with mercury, in the proportion of only 
TzcriKith part, rendered the mercury solid, 
and reduced the specific gravity from 13 to 
S. The professor likewise informed his au- 
dience, that he had decomposed the boracic 
and fluoric acids, and had en joyed a glimpse 
of their metallic bases ; and that be had fully 
ascertained, that lime, magnesia, stron- 
tites, and barytes, are compound bodies, 
each having a metallic substance as a base. 
Hence the number of simple substances, 
which, but a year ago, was estimated by 
Dr. Thomson at 38, is in a very short space 
of time considerably reduced. Chemistry, 
indeed, as a science, will probably undergo 
a complete renovation: the discoveries of 
Mr. Davy promise a total overthrow to the 
beautiful, and as it was formerly deemed, 
simple and almost perfect system of Lavoi- 
sier. The English professor assumes elec- 
tricity as a general agent of decomposition ; 
that dififerent bodies are naturally in dif- 
ferent electrical states; that by altering 
these states their affinities are altered. In 
justification of this theory, he has ascer- 
tained that oxygen, and all bodies contain- 
ing an excess of oxygen, are naturally ne- 
gative, and that all bodies containing an 
excess of inflammable pfiuciple are natu- 
rally positive. Should subsequent facts con- 
firm this theory, it is highly probable, that 
many other of the bodies, hitherto regarded 
as simple, will yield to the powers of his 
apparatus. 
Substances, imponderable, in chemistry, 
are caloric, light, electricity, and galva- 
nism : perhaps the identity of the two for- 
mer may hereafter be discovered : and like- 
wise that of the two latter more complete- 
ly demonstrated. The common character 
that they all possess is, that of not being 
subject to the attraction of gravitation ; at 
least their gravity has hitherto been inca- 
pable of appreciation, hence the term “ im- 
ponderable.” They possess the greatest 
subtilty, or tenuity ; they cannot easily be 
obtained in a separate state of existence • 
they are observed only in states of combi- 
nation, or in their rapid transition from one 
body to another. We can scarcely discover 
their specific affinities, or measure their 
force, and we are unable to trace their par- 
ticular combinations, or consider them as 
essential constituent principles of any com- 
pound. They are moreover diffused over 
.ND ADDITIONS. 
every kind of matter ; at least caloric exists 
in all bodies, and probably also the electric 
and galvanic agents. See Murray’s Chemistry, 
TELESIE, in mineralogy, a gem so 
named by Haiiy, which answers to the per- 
fect Corundum and the Sapphire ; to 
these articles the reader might be referred 
without further addition, but having di- 
rected him already IoTelesie from the ar- 
ticle Gem, we shall, in this place, give Mr. 
Murray’s description. It occurs in frag- 
ments, and is crystallized ; the form of its 
crystals being the double three-sided pyra- 
mid,^ the single six-sided pyramid, and 
the six-sided prism, variously modified by 
truncations and acuminations, Its colours 
are numerous; blue, green, red, of nu- 
merous shades, and yellow or yellowish 
white, and sometimes more than one colour 
is present even in the same crystal. It is 
more or lass transparent; its lustre is re- 
splendent and vitreous ; and it often pre- 
sents a beautiful reflection of light, in the 
form of a star: the fracture is conchoidal, 
or imperfectly foliated ; the hardness is in- 
ferior to that of the diamond, but superior 
to that of every other fossil, and not yield- 
ing to the file: the specific gravity is from 
3.9 to 4.1. 
TIME, equation of, the most usual and 
best measure of time that we have is a 
clock regulated by the vibration of a pen- 
dulum. But with whatever accuracy a 
clock may be made, it must be subject to 
irregularities, as well from the imperfection 
of the workmanship, as from the expansion 
and contraction of the materials by heat 
and cold, by which the length of the pen- 
dulum, and consequently the time of vibra- 
tion, will vary. As no clock, therefore, can 
be depended upon for keeping time accu- 
rately, it is necessary that we should be 
able at any time to ascertain how much it 
is too fast or too slow, and at what rate it 
gains or loses. For this purpose it must be 
compared with some motion which is uni- 
form, or of which, if it be not uniform, one 
can find the variation. The motions of the 
heavenly bodies have therefore been consi- 
dered as most proper for the purpose. Now 
as the earth revolves uniformly about its 
axis, the apparent diurnal motion of the 
heavenly bodies about the axis must be uni- 
form. It a clock, therefore, be adjusted to 
go 24 hours froiti the passage of any fixed 
star over the merjdian till it returns to it 
again, its rate of going may be determined 
by comparing it with the transit of any fix- 
ed star, and observing whether the interval 
