Letrs anp Bhake—On Atmospheric Carbonic Anhydride. 437 
may be acting at the same time, thus giving a mixed result. Then, 
too, a difficulty arises as to the trustworthiness of the work of some 
of the observers—the fact that they have in many cases employed 
different methods of determination, and that very few of these have 
been tested as regards their degree of absolute accuracy ; and also 
that the observers have collected their air samples at different heights 
above the ground. 
“Tn our opinion, the subject is an important one, and is worthy 
of a systematic re-investigation by a number of skilled observers, 
working in different localities and employing the same method of 
_ determination, which shall have been proved to give results which 
do not vary from the true amount by more than two or three parts 
per million of air.” 
Among the problems relating to atmospheric carbonic 
anhydride which we think are specially worth attention, the fol- 
lowing may be mentioned :— 
(1) Ls Schlesing’s Theory correct ?2—Do the oceans really act as 
regulators of the amount, owing to the presence in them of earthy 
bicarbonates and carbonates—the first (in solution) dissociating 
when a decrease below the normal occurs, the second (in suspension 
or on the ocean bed) dissolving when the reverse occurs ? 
As a consequence of this theory, latitude should influence the 
amount of atmospheric carbonic anhydride, which ought to be less 
in polar than in tropical regions. 
The great ocean currents should also have an effect, absorbing 
carbonic anhydride from the air as they pass from warmer to colder 
regions. Asa further consequence of the theory, the air of the 
northern hemisphere ought to contain more carbonic anhydride 
than that of the southern, the larger water surfaces of the latter 
being colder than those of the former where land predominates. 
And, according to Mintz and Aubin, this is actually the case, the 
figures which they give as the mean amounts for the two being 
2°82 and 2°72 parts per 10,000 respectively—a variation of 4 per 
cent. 
(2) The influence of Day and Night.—Nearly all the observers 
have found an increased amount of atmospheric carbonic anhydride 
at night over land surfaces, to account for which two theories have 
been advanced—(a) the cessation of plant activity in decomposing 
the gas, owing to the absence of light, and (0) the streaming out 
SCIENT. PROC. R.D.S., VOL. tX., PART IV. 2K 
