340 MR. J. WELSH’S ACCOUNT OF METEOROLOGICAL 
less perfect than at present), no sensible difference in the com- 
position of the atmosphere upon the surface, and at the greatest 
heights accessible to man. 
“ In quantities of air so limited as those at my disposal, it 
was not possible to determine accurately the proportion of car- 
bonic acid which they contained. Its presence however was 
distinctly shown by the formation of a film of carbonate of lead 
upon a solution of the subacetate which was introduced to a 
portion of the air confined over mercury. 
I have found a form of pipette, a sketch of which I sub- 
join, very useful for transferring small quantities of gases over 
mercury. It saves a great deal of fatigue, and I think con- 
tributes to precision in the results obtained. Its working is so 
simple as hardly to require description. It is first completely 
filled with mercury by closing the lower steel stopcock and 
opening the upper one, then pouring in mercury by the funnel 
until the metal escapes by the open end of the long bent tube ; 
the upper stopcock is now closed, the bent tube introduced 
into the jar containing the gas to be transferred, and the end of 
the tube is lifted above the level of the metal in the jar of gas ; 
the lower stopcock is then opened, mercury runs out, and gas 
takes its place ; when a sufficient quantity has entered, the end 
of the tube is depressed beneath the mercury, a little of the 
metal enters and seals the opening, the lower stopcock is closed, 
and the pipette with its contents is withdrawn: the bent tube 
is now introduced beneath the jar which is to receive the gas. 
The funnel at top is filled with mercury, the upper stopcock 
opened, and the descending column of mercury expels the gas 
into the vessel destined to receive it. 
“ I am, my dear Sir, 
“ Yours very truly. 
“ William Allen Miller. 
“ To Colonel Sykes, 
Chctirnton of the Kew Committee. 
