EFFECTS OF WINDS AND OF BARO- 

 METRIC PRESSURES ON THE 

 GREAT LAKES. 



GENERAL INTRODUCTION. 



The investigation of wind effects and barometric effects* on the Great 

 Lakes, which is the subject of this publication, is a part of a much larger in- 

 vestigation, covering a much broader field, which has been in progress since 

 the summer of 1911 except as interrupted by the Great War. The ultimate 

 object of the larger investigation is to obtain a much better formulation than 

 the engineering profession now has of the laws governing the amount of 

 stream-flow. 



Whenever it is proposed to use the water which is being delivered by a 

 river, for the development of power, for irrigation, or for the supply of a city 

 or town, one is confronted with the desirability of predicting the amount of 

 the future flow of that river and its variations. It is necessary to know, as 

 a basis for the best design of the proposed works, not only the mean flow 

 of the stream, but usually also its maximum flow, its minimum flow, and in 

 general the characteristic features of its variation in flow. The more ac- 

 curately these things can be predicted the better the design of the works may 

 be made with respect to economy and safety. The decision, in the first place, 

 as to whether the proposed works are worth while frequently turns upon the 

 predicted future flow of the stream. So, too, when it is proposed to con- 

 struct great engineering works for the prevention of damage from floods, 

 such as those now under construction in the Miami Conservancy District, 

 for the protection of Dayton, Ohio, and other nearby towns, one needs at 

 the outset accurate predictions of the future flow in the streams concerned, 

 especially of the amount of the flood flows and their duration. Any substan- 

 tial improvement in the possibilities of accurate prediction of the future 

 flow of streams would be of great value to the engineers and to humanity. 



It appeared to be probable that progress toward this ultimate object, the 

 securing of a better formulation of the laws governing the amount of stream- 

 flow, is conditioned upon first securing a better knowledge than is now 

 available of the laws of evaporation from large water surfaces, such as the 

 surfaces of lakes and rivers, and from land surfaces. 



To secure a better understanding of the laws of evaporation, it seemed to 

 be of first importance to supplement the numerous and intensive studies 



* Throughout this paper the effects of barometric pressures are termed barometric 

 effects. 



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