Deep shafts of bore holes into the earth have been suggested often as sources of heat for human use. It is doubtful, however, whether such heat supplies could be obtained. For one thing, the supposed internal heat of the earth is still nothing but a guess. It may be that the relatively slight increases of heat found as one goes deeper in existing mines are due to radioactivity in the rocks instead of to outward seepage from the internal fires. Another difficulty about utilizing earth heat is that heat moves so slowly through substances like rock, as any housewife can prove by trying to fry an egg on a brick placed over a gas flame. As soon as the rock heat immediately at the bottom of a bore hole had been exhausted heat supply would stop until more could diffuse in from the sides. Dr. Shapley's suggestion, in any event, is not to search for heat but for facts. Even in existing, relatively shallow mines, he believes, scientific laboratories at different depths under the surface might yield valuable data not now obtainable. Most scientific men will agree. Revolutionary as the idea may seem to those familiar only with the standardized laboratories of physics or chemistry, there are sound reasons why a half-dozen or so of the sciences should do precisely what Dr. Shapley suggests. At least one underground laboratory has already been installed, for Prof. E. B. Babcock of the University of California has such a workroom in the Twin Peaks Tunnel, underneath the mountain that rises above the city of San Francisco. Natural radioactivity in the rocks thereabouts is greater than normal and Prof. Babcock finds that this apparently increases new species among fruit flies. To dig out laboratory rooms a mile or so down in existing deep mines probably would cost far less than many enterprises already financed by philanthropists. Even to deepen these shafts for several miles would be much less difficult than most people imagine. Increasing heat, if it is found that heat does increase, would not be difficult to overcome had the engineers sufficient money. Ventilation and transportation to and from the surface, while too costly for the business enterprise of winning metals from very deep mines, probably would present no serious difficulty were facts the chief object instead of profit. The only question to be decided before intending benefactors of science are urged to consider some such project is whether or not the facts likely to be won promise enough value to mankind. An excellent case can be made out for answering yes. Dr. Shapley mentioned four chief lines of investigation suitable for such deep-mine laboratories: studies of gravity and of the variable length of the day, researches on the various kinds of earthquake waves, experiments on ether drift and tests of the biological effects of cosmic rays and of the rays from radium.