240 NATIONAL ACADEMY OF SCIENCES 
On February 15, 1866, the Secretary of the Treasury Hugh 
McCulloch addressed a letter to Joseph Henry, then acting 
President of the Academy, requesting that a committee be 
appointed to report to the department on the best method of 
proving and gauging alcoholic liquors, with a view to the estab- 
lishment of such rules and regulations as would insure a uniform 
system of inspection of spirits subject to duties.** Professor 
Henry accordingly appointed a committee to consider the sub- 
ject, assuming the chairmanship himself and designating as his 
associates J. E. Hilgard and M. C. Meigs. At the same time, 
F. A. P. Barnard, John Torrey and B. F. Craig were requested 
to prepare tables of standard mixtures of alcohol and water. Dr. 
Craig was not a member of the Academy. 
The chief difficulty regarding the system recommended by 
Professor Bache in 1848 was that the Tralles hydrometer, which 
was the one then proposed, gave percentage in alcohol, instead 
of percentages in “ proof spirit,” or a mixture of 50 per cent 
alcohol and 50 per cent water, upon which all commercial 
negotiations were based. While the former could readily be con- 
verted into the latter in most cases, it would lighten the labors 
of the inspectors if their hydrometers gave readings in proof 
spirits. Tralles’ hydrometer, furthermore, was not adapted for 
quick observations within one per cent, which it was necessary 
should be recorded, on account of high duty; or for gauging 
large quantities of spirits out-of-doors in inclement weather, or 
under other unfavorable circumstances. It was also found that 
the tables used by the Treasury Department were not entirely 
correct. 
In view of these circumstances, the committee set itself the 
laborious task of finding a more convenient hydrometer, and of 
preparing new tables. Its report was submitted on July 21, 1866. 
The recommendations were that following the custom of the 
trade, the strength of distilled spirits should be estimated accord- 
ing to their equivalent in proof spirits, and be expressed in 
terms of percentage of proof spirits rather than by the use of the 
“SRep. Nat. Acad. Sci. for 1866, p. 18. 
