Action of Heal ciiul Pressure on JVatcr, SfC. 61 



ascertain that the tubes broke when charged with water at 

 about the melting point of zinc, and that water may be con- 

 verted into steam in a space equal to about four times its ori- 

 ginal bulk. 



XVI. Description of a Barometer for measuring Altitudes, con- 

 structed on the Principle of the Elasticity of included Air. 

 By John Murray, F.L.S. M.W.S., 8^x. 8^c. 



To the Editors cf the Philosophical Magazine andjournal. 



1AM not solitary in having to complain of the expense, 

 non-portability, liability to fracture and disorder, (coupled 

 with difficulty in manipulation,) attendant on the common form 

 of the barometer for the measurement of altitudes. I have been 

 wearied and disgusted with their occurrence and consequent 

 disappointment. 



The sympiesometer of Adie is subject to similar objections 

 — nor is the ingenious application of the thermometer by Mr. 

 WoUaston, to ascertain the elevation by the ebullition of water, 

 entirely free from inconvenience. 



It occiu'red to me, that the elasticity of a portion of included 

 air might be enlisted into the service; and, as far as I have been 

 able to determine, the instrument (a drawing of which is now 

 submitted) will answer every purpose. It is so portable that 

 it occupies little more room than that of a common thermo- 

 meter, and reposes in a case not exceeding say 12 to 14 inches 

 long. 



It forms an elegant instrument, and I trust is calculated to 

 supply an interesting desideratum in science. — It is needless 

 to add, that the spriiig of a small portion of air at a7iy given 

 density being equivalent to the pressure arising from the gravity 

 of the whole atmosphere, calculated at the same density^ is the 

 principle on which this instrument is constructed. The sub- 

 joined explanation of its structure will convey, it is hojied, a 

 sufficiently accurate idea, and one by which any person may 

 avail himself of the invention. 



I am. Gentlemen, yours, &c. 

 London, ^.^d December, 1822. J. Murray. 



P.S. I have already intimated to you my determination to 

 take no further notice of the communications of Mr. Moore. 



J. M. 



Ex- 



