The tank for the study of pressures which arrived at the Harvard School of Public Health last Friday has presented several difficulties to the school authorities in connection with its operation.

The tank is a submarine-shaped affair 35 feet long and eight in diameter which was constructed to investigate the effect on men of working under increased and decreased pressures and also to try the cure of respiratory diseases by regulated atmospheric changes. It consists of two chambers with a lock between them, and was built for the School at Akron, Ohio, according to plans drawn by A. J. Van Woert of the Engineering School.

Keeping up a steady pressure and at the same time ventilating equally the two chambers into which the apparatus is divided has been the chief engineering problem. Pressures as high as 60 pounds per square inch or as low as those encountered at a height of five miles in the air can be obtained, but if a tiny hole for ventilation were afforded in the welded steel sides of the machine, the pressures inside and outside would immediately equalize. It is believed, however, that the difficulty has been solved by ventilating with gases already compressed or diluted.

The two chambers are now being fitted up, one as a laboratory and workshop and the other as living quarters for the men who will work in the tank, who will have to remain in it at least a week on end. It takes some 24 hours to adjust them to the change in pressure, and once in the tank, there is tremendous pressure on the door to keep them there. Only a half pound difference in pressure from that of the normal atmophere places a force of 1500 hundred pounds on the door.

In the laboratory will be rowing machines, bicycles, and other forms of exercisers, and the men will be permitted to pursue their own line of work.