378 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 51 



subsequently given up, etc. If ever these questions can be 

 solved even with only a rough approximation this will be con- 

 sidered a great advance in our knowledge. 



Then first will the many items that go to make up the general 

 problem be separately treated, and only thus will be attained that 

 point of view that must even now be kept in mind in assembling the 

 observations, if indeed we are ever to succeed in more completely 

 attaining the desired end. 



The present memoir and others to follow later will contain an 

 effort in this direction. 



After some introductory considerations I will first present a num- 

 ber of quite general theorems and then develop the individual 

 chapters. 



With reference to the order in which these individual investiga- 

 tions will follow each other, I shall not bind myself to any pre- 

 arranged sequence, but rather let it depend on my success in bring- 

 ing each of the appropriate problems to a definite conclusion. 



I will endeavor to give the statement of the general theorems 

 with the greatest rigor, whereas in treating the individual problems 

 I must often be satisfied with first approximations, as I do not con- 

 sider it proper to compute with five decimals when we can scarcely 

 be sure of the whole units, or to develop elegant formulae for a prob- 

 lem as to whose fundamental character we are still seeking for 

 light. 



But before I consider the problem proper it appears appropriate 

 first to undertake a rapid survey of the whole field and to attempt 

 by use of the most important well-known constants to obtain at 

 least a superficial idea as to the weight with which the processes 

 that are hereafter to be more accurately studied enter into the com- 

 putation, since only thus can we learn what points must be consid- 

 ered as of first importance and what may be neglected so long as we 

 cannot attain a high grade of accuracy. 



We most easily attain such a general view of the problem when 

 we seek for the quantities of heat that are necessary in order to 

 bring about certain effects at the earth's surface, and when we com- 

 pare these with the quantities that suffice to melt a layer of ice of 

 definite thickness or to evaporate a layer of water of definite depth — 

 a method of presentation that has already been frequently used, 

 especially by Haughton. 



I choose the large calory or the kilogram calory, as the unit of heat 

 the minute as the unit of time, and the meter as the unit of length, 

 unless some other is expressly mentioned. 



