July 20, 1906.] 



SCIENCE. 



73 



quence of the uncontrollable destruction 

 that would be caused by the Chagres 

 floods. The regimen of that river in con- 

 nection with the rainfall on the isthmus 

 has been a subject of such extensive and 

 careful investigation that the elements en- 

 tering the problem of control are now com- 

 paratively well known. Instead of the 

 floods of the Chagres playing such a de- 

 structive part in the history of the canal, 

 there have now been devised a number of 

 methods of effective control, so that it can 

 be actually demonstrated that such floods 

 are not to be feared in any respect what- 

 ever. Indeed, if a lock plan should be 

 adopted for construction, it would be im- 

 possible to feed the locks with sufficient 

 water for navigation were it not for the 

 supply offered bj the Chagres River. In 

 other words, the Chagres would play the 

 part of a friendly agent rather than that 

 of a vicious enemy in the maintenance and 

 operation of the canal. While this river is 

 subject to rapid variations of discharge, so 

 that within a period - of twenty-four or 

 forty-eight hours it may change its char- 

 acter from that of a quiet, inoffensive 

 mountain stream to a literally raging tor- 

 rent, the range between low water and 

 flood elevations is much less than in many 

 of our American rivers. Nor are the ex- 

 treme floods so formidable in character as 

 they have sometimes been supposed. While 

 many small floods occur every season, a 

 high flood is a rarity, as but five have oc- 

 curred within fifty years, and in no case 

 have these high fiood effects lasted more 

 than about forty-eight hours. One of the 

 prominent characteristics of the Chagres 

 floods is the rapidity with which they rise, 

 the short period of highest water and the 

 short time required for recession to the 

 condition before the flood began. 



Records of accurate daily observations, 

 both self-recording and otherwise, of the 

 discharge of the Chagres under all condi- 



tions of flow have been kept for nearly 

 twenty years, and more or less complete 

 observations for a much longer period, so 

 that what may be reasonably expected of 

 the river at all seasons of the year is now 

 fairly well known. 



In addition to the discharge observations 

 along the Chagres River, accurate rainfall 

 records have for many years been kept for 

 all portions of the isthmus. The amount 

 of rainfall varies greatly both from cer- 

 tain portions of the year to other portions, 

 and from one year to another. The 

 isthmian year is divided into two parts, 

 the wet season and the dry season. The 

 former begins about the latter part of De- 

 cember and usually extends to the latter 

 part of April, the remainder of the year 

 constituting the dry season. During the 

 dry season but very little rain falls; some- 

 times none at all for long periods. An 

 erroneous impression may easily be re- 

 ceived from the term wet season, which 

 does not mean that rain falls daily, or that 

 it often rains all day. In reality, some of 

 the most enjoyable weather of the entire 

 year is found in the rainy season, when 

 there is no dust and the general tem- 

 perature is agreeable. The rain falls 

 mostly in showers, although there are con- 

 tinuous rain storms extending over several 

 days. The latter, however, are not com- 

 mon. The average annual rainfall is not 

 far from 130 inches at Colon and on the 

 Caribbean side of the isthmus, but on the 

 Pacific side at Panama the annual precipi- 

 tation is only about one half as much. 



These excessive rainfalls and the prox- 

 imity of the two oceans produce at nearly 

 all times an atmosphere of high humidity. 

 The trying character of the isthmian cli- 

 mate is due chiefly to this feature. The 

 temperature usually runs from 70° to 75° 

 F. in the morning, and to 82° to 86° F. in 

 the hottest part of the afternoon. Occa- 

 sionally the temperature rises to 96° or 98° 



