.1826.] 0« the Measurement of Heights hy One Barometer. 33 



Article VII. 



On the Measurement of Heights hy One Barometer, with the 

 requisite Tables. By Mr. J. Nixon. 



(To the Editors of the An7ials of Philosophy.) 



GENTLEMEN, Leeds. No.. 1825. 



It is so rare to have at command in the course of a series of 

 barometrical observations the uninterrupted co-operatiou of an 

 intelligent friend, and so hazardous to the safety of the instru- 

 ments as well as to the accuracy of the observations, to entrust 

 them to strangers, that most generally recourse will necessarily 

 be had, especially by the geologist and botanist, to the less 

 accurate and more tedious method of ascertaining the altitudes 

 independent of the observed contemporaneous heioht of the 

 barometer at the lower station. To point out such\ plan of 

 operations and to furnish such tables as, it is presumed, will 

 insure to the method all the accuracy and facility of which it 

 may be susceptible, is the proposed object of the present article. 

 Ihe description of barometer best adapted for the labours of 

 the geologist &c will be that of Sir H. Engleheld. The mercu- 



IniTnTH./"''^.''' Ttr^^ ^"S^^' P^^^^^tly continuous, 

 and unstudded with air-bubbles, or hnzy nebulce. The vacuum 

 above being perfect, a very gradual inclination of the tube will 

 suffice to produce a smart blow the moment the column comes 



^nwlTb/n l/^V""T''-"^'^^^ ^"'^^' otherwise the concus! 

 nor-.l ^1 ^"-^ "^^'-'y maudible ; the mercurial column will 



occasionally appear broken or divided, and will rarely measure 

 on being disturbed or exposed to a different temperature! pre: 

 cisely the same corrected height. ^ 



(nU'LT^u 5f ^"^ P^-'""' V '^"^'^^ '"^^' ^^'^^"'d be engine-divided 

 not enamelled) into inches and twentieth parts. The vernier 



nr25 Tnulf""\ ^^.'^P'-^hending a space of 1-2 inch subdivided 

 into 2o equal parts, ,s more accurately moved by a milled-head 

 nut and endless screw than simply by the hand! A brass ri no- 



and h > ?f ''"^"^ f '^^^^ '' *' ' ^•^"^'-- -^braces the tube^ 

 and has its (base, or) under edges perpendicular to the mercurnl 

 column and precisely of the° height of zero of he vern S 

 Baro.^,eters furnished with a triang^r notch of brass in Xu of 

 the nng subject the observer to the risk of measu rn^ the 

 height o( the column as affected by parallax. "'"'''"""=> ^^^ 

 Ihe scale must be so affixed that its zero may coincide with 



ueing u. J his is effected by raising the scale a quanti v eouil 

 to the correc ion for capillarity subtracted from the neu ral n^oin 

 divided by the capacity plul I.* The capacity being l-Sulh, 



New 5en-J,^ot'lf '" "' " S ""' " "°* '""""^ """''• 



