To the Editor.—
In the Nov 6, 1972 issue of The Journal, Dr. Ronald M. Sommer submits a letter regarding the capacity of a scuba diving tank (222:705, 1972). It is apparent from the information published that Dr. Sommer did not do his homework on the physics of diving and the gas laws involved. Had he done so, he would have found that his 70-cu ft of air single tank, which he states would last 70 minutes at sea level (that presumes a use rate of 1 cu ft/min) would last 35 minutes at 33 feet, 21 minutes at 36 feet, and 17.5 minutes at 99 feet. Dr. Sommer had the right idea but his mathematical progression was wrong.