O weld the two tubes together at the center of the earth was a most delicate operation; but the work was performed with the greatest care, and the doctor was highly gratified to find his labors crowned with success.

Then the boring-screws and other instruments were withdrawn, and specially constructed pumps were set in operation to exhaust the tube of air. This work was supplemented by the use of ingenious chemical processes to absorb the greater part of the rarefied air which the pumps and other apparatus were unable to remove.

This precaution was absolutely necessary, for, as already stated, air presents an enormous resistance to objects which are traveling at a great velocity. Air in the tube would not only have retarded the car considerably in its passage, and