May 11, 1917] 



SCIENCE 



447 



particularly true in the field of natural 

 science, where the laboratory is the world 

 itself, a portion only of which can be 

 brought under the observation of any one 

 individual. Geological processes are differ- 

 ent both in degree and in kind according as 

 they are studied under conditions of aridity 

 or of excessive humidity, under tropic heat 

 or polar cold. It is unquestionable that 

 geology having developed as a science in 

 those temperate regions of moderate humid- 

 ity which have permitted a high degree of 

 civilization, is correspondingly defective, 

 and must be modified if it is to be universal 

 in its scope. The physical geology of 

 deserts has been studied seriously only 

 during the present generation. It is within 

 the last decade only that the attention of 

 geologists has been focused upon the sub- 

 polar latitudes, and the geology of the 

 tropical jungles is yet to be written. 



To indicate how the peculiar environ- 

 ment, the conditions of the time, and the 

 special activities of the individual have left 

 their impress upon a well-known theory, I 

 may cite the ease of Robert Mallet and his 

 centrum theory of earthquakes, a theory 

 which received general acceptation and was 

 orthodox doctrine among earthquake spe- 

 cialists for full half a century. Robert 

 Mallet was educated as a civil engineer, and 

 in 1831 became a partner with his father in 

 the foundry industry at Dublin. During 

 the Crimean "War he constructed monster 

 mortars of thirty-six inch caliber which 

 embodied new ideas and were completed in 

 1854. Thus becoming interested in ballist- 

 ics, he made a thorough investigation of the 

 strains developed by explosions in the 

 chambers of guns, and a monograph upon 

 the subject which he published in 1856 

 brought him general recognition and many 

 honors. A year later, in 1857, occurred 

 the great earthquake in the Basilicata, 

 generally referred to as the "Great Neapol- 



itan Earthquake," since the district was 

 included in the former kingdom of Naples. 

 Believing himself by reason of his studies 

 of explosives to be specially fitted to in- 

 vestigate this disturbance. Mallet applied 

 to the Royal Society for a grant of money, 

 and his request being approved, he visited 

 the Basilicata, and in 1862 in two sumptu- 

 ous volumes the earthquake was explained 

 as the result of an explosion that had 

 occurred in a cavity beneath the region 

 affected, the damage upon the surface being, 

 explained under the laws of transmission 

 of stress such as had applied in his earlier 

 researches upon cannon. No one familiar 

 with these circumstances can reasonably 

 doubt that the trend of his theory was 

 already determined by his life history be- 

 fore his sailing from England. It should 

 be added that through giving to the problem 

 of earthquakes a mathematical treatment. 

 Mallet's study had the effect of removing 

 seismology from the field of geology for the 

 period of nearly half a century, and giving 

 it over to the elasticians. 



It has not been altogetlier uncommon for 

 students of science, and even those of the 

 highest rank, when drawing conclusions, to 

 fail to take proper account of the fact that 

 the observed rates of change, or gradients, 

 perhaps of temperature or pressure, which 

 they have been able to verify for limited 

 distances only, may not be assumed to con- 

 tinue indefinitely without interruption or 

 variation. No less distinguished a physi- 

 cist than Helmholtz on the basis of the 

 known aero-thermic gradient as determined 

 over Europe to a height of about nine kilo- 

 meters, declared that the atmosphere could 

 not extend beyond twenty-seven or twenty 

 eight kilometers from the earth's surface, 

 since the absolute zero of temperature 

 would be reached at that level. Sounding 

 of the atmosphere has since been carried 

 to fully twice the limit fixed by Helmholtz, 



