XXX 
REPORT- 1854. 
ing in the third and fourth was much more moderate, the greatest difference 
between the extreme readings in either having never been observed to be more 
than 0 - 02 and seldom above (K)15, thus giving 0*01 as the limit of error of 
an observation from this cause. The barometer No. 5 showed, of course, 
even less oscillation, the extreme readings not differing more than 0 - 01. 
The circumstances under which these numbers were obtained were, I believe, 
favourable to a just estimate of the amount of contraction necessary, as there 
was both in the passage to Jersey and back a considerable amount of swell, 
there having been on the previous day a heavy gale blowing. 
“ Considering that the existence of a small quantity of pumping must at all 
times be desirable, in order to secure a more free action of the mercury than 
if the barometer were suspended quite steadily, I am of opinion that baro¬ 
metershaving their tubes stopped to about the same extent as in Nos. 3 and 4, 
would, ou the whole, be the most generally convenient and accurate, whilst 
even a greater degree of contraction would do no great harm. I would, there¬ 
fore, recommend that the contraction should bo from about 18 to 25 minutes. 
‘I have both before this trial and since made a series of comparisons 
between the standard by Newman and these barometers. I have found that 
all the barometers follow the standard very consistently. There is, how ever, 
one circumstance which should be noticed, and which I have before to some 
extent mentioned to the Committee. The marine barometer does not act 
quite freely when suspended at rest. The standard barometer is always, to 
mZlr : eXU ^’ *fi advance of the marine barometer; that is, when the 
falliiiCT^ S | r,91 | fl ^’ barometer is below the standard, and when 
0*0 FJh. | bov , e ?'■ Ih ® am . onnt of ‘his retardation I find to he about 
whatever il»> ,\ W lut V? m ‘her singular, it exists to about the same extent 
the vromil °i c ?" trac,ion ‘he tube, although that has varied in 
observed when rh»m ‘ '• retardation, it should be remembered, has been 
,n i , barouictorhaa been left quite rest, a condition 
ceive a !£ y ever obt « m at , saa > "bore there will generally bo, I con- 
oscillation in the cXmn f ni0ti< , >n to P r «duce a certain small degree of 
oscillation at all exists the pSh? 5 un<J _ ,t l ls evident that so long as any 
and the reading of the’inof et l u, h l>r |uni of the mercury will be maintained, 
reading of the instrument will show the true barometric pressure. 
“ J - “ 1 •* d - «r. >— fcithfcur. . 
' . “J. Welsh. 
m Jhe barometer as now constructed is thus described by Mr. P. Adie, the 
the tube near the raWd"^^^cSl^b 1 "’ °’ 25 in * About 4 inches of 
raetmn necessary to prevent inconvenient^-iV* ? rder to Produce the con- 
is first V0SSe ’ I he degree of contraction n ? lo jJ nt s,;a frotn ihc motion 
*1 , suspended, the mercury requires H hn * cb * ,,a ‘> when the barometer 
at, ‘ 1P 4 ? be to * prop/rK"A'^"ty minutes to fall from 
the cistern 1 ; ° j The lower crftffftaET ” r 
e cistern, M also contracted Wltf a ' b ’ wh,ch is w ithin the 
Se itXtn I* S 
“The cistern J5rr ly l,0il - fi in ‘he tube ji th/ ^entne deteriorated. 
" of the °PP er part of the ci.tern 
into 
