REPORT OF THE COUNCIL. XXIX 
“1st. Any one of the three barometers is capable of showing at sea the 
changes of pressure, with a probable error of about 0 005 inch, or at most 
0-007 in. 
“ 2nd. The tremor of a steam ship is rather beneficial than otherwise to the 
performance of the barometer, and (leaving the pumping out of considera¬ 
tion) the barometer performs rather better at sea than on land. 
“3rd. For such a motion of the ship as must be very common, the 
amount of contraction of the tube should be greater than in any of tin- 
three barometers employed, say a contraction to 18 or 20 minutes. The 
mean amount of pumping from ten observations in the return voyage was, 
for the tube contracted to 5 minutes 0-064 in., and for the one contracted 
to 10 minutes 0-031 in.; the greatest observed being for the former O' 13 in., 
and for the latter 0*05 in. In order, therefore, to reduce the pumping so 
that the probable error of an observation from this cause may not exceed 
OOl in., the contraction should be to 20 minutes at least 
“4th. It appears to me very desirable that each ship should be furnished 
with two barometers — one for calmer weather and the other for rougher— 
the former having the tube contracted to 10 or 12 minutes, and the latter 
to about 25 minutes. This would render good observations obtainable in all 
stales of the weather; and if occasional comparisons of the two were taken, 
would, besides obviating to some extent the inconvenience arising from an 
accident to one, afford the means of checking any changes which might occur 
in the zero-points of cither instrument. If, however, two barometers cannot 
be supplied to each ship, I am disposed at present to think that a contrac¬ 
tion to about 1.5 or 20 minutes would bo generally the most convenient. 
“The mode of suspension and the means of observation adopted in Mr. 
Adie’s barometers seem very suitable, the spring of the suspending arm being 
quite sufficient. The arm should perhaps be a little longer, say 2 inches more. 
“I should mention, that the two steamers were about 700 or 800 tons 
burden. 
*J. P. Gassiot, Esq., P.R.S., “ I am, yours faithfully, 
Chairman of the Kew Committee.” “ J. Welsh.” 
“Kew Observatory, May 25, 1851. 
“My dear Sin,—In compliance with a wish expressed by the Kew 
Committee at their Meeting on May 3rd, 1 proceeded to Southampton on 
the 8th instant, and made arrangements for a further trial of the marine 
barometers in one of the South Western Kailway Company’s mail steamers 
plying to the Island of Jersey. Having been furnished by you w ith a recom¬ 
mendation from Mr. Tite to the Secretary of the Company's steamers. I was 
most readily provided with the best accommodation which could be got in the 
ship, and received every attention and assistance from Mr. Balmt, the captain. 
“ file principal object contemplated by me in this trial, was the deter¬ 
mination ol the amount of contraction required in the tube for the prevention, 
within convenient limits, of the pumping of the mercury. 1 took with me 
five barometers by Adie, all of the same general construction, but differing 
in the amount of contraction in the tubes. They were stopped in tho fol¬ 
lowing proportions—5, 10,18, 21 and 35 minutes for the times required for 
Uie mercury to sink from the top of the tube to its true height after the 
barometer is placed erect. 
“ I found, as on the previous trial to Leith, that the first two were not 
nearly sufficiently contracted, the amount of pumping being indeed so great 
that good observations could not possibly be taken with either. The pump- 
