the altitude of the planet, the relative situation of the planet and
moon, with any other circumstances of twilight or haze that were
likely to cause any incorrectness in the observation. To obviate the
uncertainty that will always attend the results of such observations,
from different states of weather, difference of telescopes, and imper-
fection of vision in different observers, Mr. Goldinghaxn recommends
not to draw any inference from comparison of corresponding immer-
sions alone, without attending to the difference of corresponding-
emersions also, by which all sources of error will be in a great degree
corrected.
In the last Bakefian lecture mention was made of an apparent decomposition of bar'ytes and strontites into oxygen and inflammable matter.
In the prosecution of the same course of experiments upon lime and magnesia, similar results were obtained; for when either of these earths was slightly moistened with water, and thereby rendered a. conductor of electricity from a powerful voltaic battery, inflammable matter was developed at the negative surface, and oxygen at the po- sitive. And these phenomena were not dependent on the presence of water; for when the same earths were made conductors, by being- in a state of fusion with boracic acid, analogous appearances Were produced.
On account of the high inflammability of these bodies, similar ex- periments were conducted under naphtha, with the hope of preserving the products for examination ; but although dark opake specks, having in some cases an appearance of metallic splendour, were produced, yet, when heat was applied to them under boiling naphtha, there was no appearance of fusion, and consequently no separation from the surrounding undecompounded earth; but when the mass was afterwards thrown into water, an efl'ervescence occurred, and evident decomposition of the water.
A series of experiments were next undertaken upon mixtures of barytes or strontites, of lime or magnesia, of alumine or silex, with potash; and in the case of bar-ytes and strontites, the potassium formed was evidently not pure, but apparently alloyed by another metallic substance.
When barytes, strontites, or lime, was mixed with oxide of silver or mercury, the compounds afforded analogous results when acted on by the voltaic battery.
When these experiments were resumed, after an interval of several weeks. a battery had been prepared with 520 pair of plates; and an attempt was then made to unite the bases of these earths with the
