March 13, 1896.] 



SGIENGE. 



409 



all miads, from that of the lowest animal to 

 that of the highest human genius" (p. 269). 

 What is this mind, of which the author speaks ? 

 And what is meant later by the author's division 

 of reality into ' the material world ' and ' the 

 mental world ' (p. 271), or ' the material world ' 

 and ' the spiritual world ' (ibid). If we are deal- 

 ing with indissociable constituents of matter, 

 would it not be as wise to speak of ' the material 

 world' and 'the world of duration,' or 'the 

 material world' and 'the world of motion?' 

 But I waive these questions, as being possibly the 

 products of a ' feverish dream. ' It must be 

 accepted as a general answer to all such, and a 

 sufficient consolation to the discontented, that 

 'the simple and the true remain ' (p. 271). 



As a last word I may add that the more sober 

 of the philosophers of our time have, notwith- 

 standing 'the intoxication of illusion,' been ac- 

 customed to think that it is not prudent for a 

 philosopher who has no special knowledge of 

 the subject to venture into other fields, as, for 

 example, that of anthropology. Some even go 

 so far as to believe that it is not wise for an 

 anthropologist to venture into philosophical dis- 

 cussions unless he has acquainted himself with 

 the writings of those who have preceded him in 

 work of that kind. Perhaps it is because they 

 are ' immersed in thaumaturgy ' that they find 

 in such contributions to philosophical literature 

 more heat than light. 



George Stuakt Fulleeton. 

 University of Pennsylvania, February 27, 1896. 



THE TEMPERATUEE OF THE EARTH'S CRUST. 



In the December number of the Journal of 

 Science Prof. Alexander Agassiz gives the 

 temperatures found at different depths in a 

 well-known mine in the Lake Superior region, 

 as follows: 



At 105 ft.— 59° F. 



At 4580 ft.— 79° F. 



Or an increase of temperature of 1° F. for 

 each 223.7 ft. 



With this he compares Lord Kelvin's figures 

 of 1° in every 51 ft; also the figures obtained 

 in the St. Gothard tunnel, showing a rise of 

 1° for every 50 ft. 



The Lake Superior figures would make the 

 solid crust of the earth nearly 90 miles in thick- 



ness, instead of Lord Kelvin's deduction of 

 twenty miles. 



Now I wish to suggest,as a tenable hypothesis, 

 that the Lake Superior district having been far 

 in 1 the heart of the ice cap of the glacial period, 

 the refrigeration of the crust of the earth pene- 

 trated to so great a depth that its effects still 

 linger. 



Take, for example, the 100° C. line, which 

 normally is 9,000 feet below the surface. Dur- 

 ing the many thousand years of the ice cap 

 this may have been forced downwards to a 

 depth of, say, 40,000 ft. Since the removal of 

 the ice, during, say, 7,000 years, the internal 

 heat has been slowly rising towards the surface. 

 But it has not yet had time to regain its former 

 levels of temperature. 



It would be interesting to ascertain what are 

 the rates of increase of temperature now under 

 regions where the subsoil is permanently frozen, 

 as in the tundras of Siberia and Alaska. 



It does not seem clear to me that the earth's 

 crust necessarily became greatly thickened in 

 the Superior region. The refrigeration need 

 not have penetrated deeply enough for such an 

 effect. Sbreno E. Bishop. 



Honolulu, January 24, 1896. 



THE X-RAYS. 



Shortly after mailing my note of last week 

 I took a photograph by means of the X-rays, 

 using a Crookes' tube connected with an induc- 

 tion coil actuated by a make and break current, 

 and therefore giving the electrodes a fixed po- 

 larity. 



The photograph shows only one electrode 

 which, from the manner in which the tube was 

 connected, was the cathode, thus confirming the 

 views expressed in my previous letter. 



Ralph R. Lawrence. 



Boston, March 5, 1896. 



the instinct of pecking. 

 In discussing Prof. Morgan's lecture on in- 

 stinct it has several times been stated that 

 chickens pecked instinctively, but had to be 

 taught to drink. There was a note in Nature 

 last year, concerning some species of Asiatic 

 pheasants — it may possibly have been the Jun- 

 gle Fowl — to the effect that the young did not 



