232 Trigonometrical Survey.—Eruption of Vesuvius. 
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flame of the safety-lamp is extinguished, and which burns in every 
mixture of carburetted hydrogen gas that is respirable. It con- 
sists of a slender metallic tissue of platinum, which is hung in the 
top of the interior of the common lamp of wire gauze, or in that 
of the twilled lamp. It costs from 6d. to 1s., and is imperish- 
able. This tissue, when the common lamp is introduced into an 
explosive atmosphere, becomes red hot, and continues to burn 
the gas in contact with it as long as the air is respirable; when 
the atmosphere again becomes explosive, the flame is relighted. 
I can now burn any inflammable vapour either with or without 
flame at pleasure, and make the wire consume it cither with red 
or white heat. I was led to this result by discovering slow com- 
bustions without flame, and at last I found a metal which made 
these harmless combustions visible.” 
TRIGONOMETRICAL SURVEY. 
Dr. Olinthus Gregory and Colonel Mudge, who it will be re- 
collected formed a part of the scientific association which lately 
proceeded to the Zetland Isles, have just returned. Captain Col- 
by and M. Biot remain in Zetland a few weeks longer ; the for- 
mer for the purpose of terminating his observations with Rams- 
den’s zenith sector, and then of connecting the chief points in 
the triangulation; the latter, in order to witness the phenomena 
of the Aurore Boreales in these high latitudes. Dr. Gregory 
having ascertained what is technically devominated ‘ the rate” 
of Pennington’s astronomical clock at Balta, in north latitude 
60. 45, proposes staying a short time at Aberdeen, for the pur- 
pose of ascertaining the rate of the same clock there, by means of 
astronomical observations with the excellent instruments in the 
Observatory at Marischal College. 
ERUPTION OF VESUVIUS. 
A letter from Naples, dated July 20, says—‘‘ The present 
eruptions of Vesuvius are astonishing. Copper, iron, alkaline 
acid, sulphur, sulphuric acid, chalk, and ammonia, form salts that 
are sometimes in a mass and sometiines divided. It is observed 
that copper is very much mixed with volcanic matter; quantities 
of it are found among the different kinds of lava. Vesuvius, which 
since the year 1813 has been more or less in a state of commo- 
tion, has entirely covered its former crater with a thick crust, 
over which the new eruptions have thrown two little mountains, 
from which come smoke, ashes, and vitrified stones. The earth 
is covered with bits of transparent glass. This crust is so consi- 
derable, that, if it isnot propped up, the sinking of the matter 
composing it will produce an effect like that of the eruption which - 
took place in the time of Titus.” 
NAUTICAL 
