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XIV.—Further Experiments and Remarks on the Measurement of Heights by the 
Boiling Point of Water. By James D. Forzes, D.C.L., F.R.S., Sec. B.S. Ed., &c., 
Professor of Natural Philosophy in the University of Edinburgh. (With a 
Plate.) 
(Read 4th December 1854.) 
_In 1843 I presented a paper to the Royal Society of Edinburgh, giving an 
account of experiments made on the boiling point of water in the Alps, un- 
der various barometric pressures. My object was twofold: first, to describe an 
apparatus which I considered more practically available than those previously in 
use; and, secondly, to give a simple, and, as I believed, new formula for comput- 
ing heights from such observations. 
With reference to the second point, I became aware, some time after the pub- 
lication of my paper, that Sir Joun Leste had proposed to compute heights by 
the thermometer, assuming the change of the boiling point to be ewacily in pro- 
portion to the height ascended. While cheerfully conceding to Sir Joun LrEsiie 
priority on this point, I submit that he did not bring forward experiments to 
justify its practical adoption. 
Of late years both the instrument and the formula have been objected to by 
M. Reenautt of Paris, and the latter by Dr Joserpn Hooker, who finds that it 
_ does not correctly represent his Indian observations. This has caused me to 
examine the whole subject, and also Dr Hooxer’s observations on the boiling 
point, with the particulars of which he has kindly furnished me, and I proceed 
to lay the details before the Society. 
; In 1843, when I wrote, the method of determining heights by boiling water 
had fallen very much into abeyance, principally owing, as I believed, to the 
inconvenient instruments employed, and partly to the uncertainty of the deduc- 
tion of heights. As the thermometric method is principally valuable when baro- 
_ meters cannot be safely transported, and must always be inferior in accuracy to 
_ good barometric results, my intention was to do a service to physical geography, 
_ by introducing a convenient and effective instrument, by means of which water 
_ could be certainly made to boil even in untoward circumstances, and the tempe- 
rature ascertained, not to the illusory nicety of two or three decimals of Fau- 
RENHEIT’S degree, as Archdeacon WotLaston attempted, but to within about 
zoth of a degree, corresponding to about 25 feet of elevation, which I stated as 
_ the utmost degree of accuracy which I expected to attain, even in favourable 
_  «-*-VOL. XXI. PART Il. i 3R 
