122 MEMOIR OF THE LATE DR. HENRY. 
tic researches. Subsequent experience has de- 
monstrated, it is true, the unsoundness of these 
projects for enriching with new resources, the 
art of practical medicine. But the beautiful 
law, unfolded by the genius of Gay Lussae, 
that the gases combine in volumes which are 
either equal or multiples by an integral number, 
—by establishing, when interwoven with the 
Daltonian philosophy, the existence of some 
simple relation between the numbers of atoms 
existing in equal spaces of aeriform matter, has 
almost elevated the pneumatic chemistry to the 
dignity and exactitude of a mathematical sci- 
ence. There is, moreover, in the pursuit of 
these subtle elements, which escape the visual 
sense, which can be imprisoned and weighed 
only by the most refined instruments, and which 
can be discriminated only by the most delicate 
processes and indications, a somewhat of mys- 
tery and of a higher initiation, which deeply 
moves the imagination. It may too be safely 
affirmed, that Dr. Henry’s habits of extreme 
mental accuracy, his unrivalled manual expert- 
ness, and the general tendencies of his tastes 
towards elegance and precision, peculiarly qua- 
lified him to excel in conducting such delicate 
enquiries. 
