LATER YEARS 403 



the temperature of the earth increases as we dig into it. 

 From hitherto recorded observations Lord Kelvin had 

 assumed that the temperature increases 1° F. for e very- 

 Si feet of depth ; while observations in the St. Gotthard 

 Tunnel gave an increase of 1° for 60 feet. From these 

 observations it had been calculated that the crust of the 

 earth would be about 20 miles thick for Kelvin's gradi- 

 ent, or about 26 miles for the other. 



The deepest point in the Calumet Mine at the time of 

 this investigation was 4712 feet (vertical depth). Holes 

 ten feet deep were drilled in the rock at various points 

 from 150 feet to 4580 feet, standard slow-registering 

 thermometers were inserted, the holes plugged with 

 wood and clay ; and the thermometers were left from 

 one to three months. The temperature of the rock at 

 4580 feet proved to be only 20° F. hotter than that at 

 150 feet. This gives an average of 1° F. for 223.7 feet, 

 which by the same reasoning as that based on former 

 experiments would give a thickness of the earth's crust 

 of over 80 miles, instead of 20 and 26 miles. Agassiz 

 never offered any explanation to account for the extra- 

 ordinary difference in his temperatures from those ob- 

 tained in other parts of the world, though it has been 

 suggested that it might be due to the cooling effects of 

 the neighboring waters of Lake Superior. He once said, 

 however, that the article had given rise to more annoy- 

 ing correspondence than anything else that he had ever 

 written. 



In the fall of 1902 the friends of Mrs. Louis Agassiz 

 arranged for the celebration of her eightieth birthday 

 by subscribing to a building for Radcliffe College, of 

 which she had long been President. A concert was also 

 given in her honor at the theatre in Memorial Hall. As 



