220 Analysis of the Substance 
trivance is applied to the cabin stove, and I should think 
might, with equal advantage, be applied to dwelling-houses 
in situations where eddy winds are apt to occasion smoke. 
But what attracted most of my attention was the manner 
in which the track-rope is attached to the vessels ; and which, 
Tam informed, has prevented many dangerous accidents, to 
which they were formerly liable. There is a contrivance 
by which it may be instantaneously disengaged by a kind of 
trigger, a plan and profile of which are sketched in figures 
4. and 5. 
I, represents the end of the track-rope. 
K, a pin firmly connected with the frame, which is bolted 
to the deck above the cabin. 
KL, a lever, the end K of which preponderates, and 1s so 
formed as to allow the loop on the end of the track-rope I, 
to remain on the pin K, while the horses are pulling pro- 
perly forward; but should any accident occur, and endanger 
their being dragged into the water, all that is necessary is 
for a person to put his foot on the end L of the lever; which 
end being thus depressed makes the end K to rise, and 
along with it the loop of the track-rope is raised, which, 
getting to the top of the pin K, is instantly disengaged. 
These contrivances (figs. 4. and 5.) are placed one on 
each side of the roof, at HH, so as to leave the roof of the 
cabin quite free and safe for the use of the passengers; and 
here seats are placed, where they may enjoy the air, and the 
beautiful scenery which so often presents itself in the pro- 
gress of the voyage. 
I remain, dear sir, yours, &c. 
Glasgow, ROBERTSON BUCHANAN. 
November 20, 1806. 
XXXVIT. Analysis of the Substance known by the Name 
of Txrquoise. By M. Bouriton Lacrance*. 
Severat mineralogists have placed the turquoises among 
the calcareous bodies and those bodies which are called the 
* From Annales de Chimie, tome lix. p. 180. 
opake 
