114 MEMOIR OF THE LATE DR. HENRY. 
tion of the same gas under varying pressures, 
Dr. Henry arrived at the simple law “that water 
takes up of gas condensed by one, two or more 
additional atmospheres, a quantity which ordin- 
arily compressed would ‘be equal to twice, 
thrice, &c., the volume absorbed under the com- 
mon pressure of the atmosphere.” This exact 
proportionality, of the quantities absorbed to the 
pressures, makes strongly in favour of the theory 
proposed by Dr. Dalton, that the absorption of 
the gases by water is due entirely to mechanical 
agencies. 
Dr. Henry described in the Philosophical 
Transactions for 1808, a form of apparatus, 
adapted to the combustion of larger quantities 
of gas than could be fired in eudiometric tubes. 
Results were thus obtained, which may be 
pronounced fair approximations to truth, espe- 
cially when estimated with reference to the still 
imperfect resources of pneumatic chemistry. 
The apparatus cannot however be now recom- 
mended when extreme precision is desirable. 
In this year, 1808, he was elected a Fellow of 
the Royal Society, and in the following year 
received by the award of the President and 
Council, the medal on Sir Godfrey Copley’s do- 
nation, as a mark of their approbation of his 
