CORRASION BY GRAVITY STREAMS. 207 



so far discovered are excessively simple, and it would seem 

 that ingenious and complicated explanations of natural 

 phenomena scarcely need serious attention. Nevertheless 

 that which is easily understood when discovered may only 

 with great difficulty be brought to light for the first time. 



The chief difficulties in this connection lie in the general 

 lack of the "scientific use of the imagination" by the 

 ordinary investigator, and in the ephemeral existence of 

 man, the individual, as compared with the duration of the 

 activities he may be considering. To make up for this lack 

 of imagination while conducting scientific investigations a 

 valuable suggestion is often afforded by the chance obser- 

 vation of an "end result" which one has obtained in a short 

 period of time, and which is similar in a general way to 

 the one under examination. Especially valuable is such a 

 suggestion when the various steps in the process of the 

 development of the chance "end result" may be readily 

 seen and appreciated. 



Such similar "end results" may have been obtained by 

 experimenting with substances quite different from those 

 in which the special "end result" that the scientist is 

 investigating has been reached. Furthermore the activities 

 concerned in each case may not have been identical. 

 Nevertheless, such suggestions frequently have led to 

 actual proof of the particular problem which may have 

 been under consideration. As an illustration of this we 

 may mention the special case under consideration, namely, 

 the common principles underlying gravity 1 stream action 

 and the application of such principles to ice action. It will 

 be seen, as the following notes are read, that the under- 

 lying principles of ice-stream action could scarcely have 

 been appreciated by a study of modern glaciers only, but 



1 Throughout this note the word "stream" will be used instead of 

 the term "gravity stream." 



