THE MISSISSIPPI VALLEY. 19 



OF THE DRAINAGE OF THE OHIO. 



We are but little aided in the determination of the facts attending the drain- 

 age of a country, and the discharge of its rivers, by the previous labor of phi- 

 losophic vi^riters. The investigations of this subject have been confined, almost 

 exclusively, to the measurements made by engineers of the volume of w^ater 

 which certain inconsiderable streams would furnish during periods of drought, 

 for the use of navigable canals depending on them for supply. No systematic 

 experiments on a large scale, with a view to the determination of the daily and 

 annual discharge of great rivers, and the comparison of that discharge with the 

 annual fall of rain for the climate, so as to obtain the amount consumed by 

 vegitation and evaporation, over wide areas, have ever yet been instituted. 



There has, perhaps, never been presented any practical or commercial enter- 

 prise, depending on these facts, to elicit an investigation necessarily laborious 

 and costly. The experiments of the writer on the discharge of the Ohio, at 

 Wheeling, will, it is hoped, to some extent, supply this void, and furnish a basis 

 for valuable scientific and economical conclusions. 



These experiments were prosecuted during the spring and summer of 1849, 

 for the purpose, mainly, of ascertaining the practicability and cost of supporting 

 the navigation of the Ohio, by supplying the channel with water from reservoirs 

 properly constructed upon its tributaries. The results, it is believed, are not 

 only valuable in establishing this fact, but also of interest as contributions to 

 theoretical and practical science. 



The site chosen for these experiments was a space along the Ohio, from the 

 village of Martinsville, above Wheeling, to the Burlington quarries. A portion 

 of the river, 10,063 feet in length, was measured off" and divided into four 

 sections. This portion was carefully surveyed and sounded. The width of the 

 surface was determined from point to point by triangulation with a theodolite, 

 and the depth from a series of several hundred soundings. 



The observations for the velocity were made on a float properly loaded, and 

 suffered to descend by the force of the current in the thread of the channel. 

 The observer kept alongside of the float, and followed it down in a steamboat, 

 noting the time as it passed the ranges previously established at the several sta- 

 tions on the Ohio and Virginia shores. 



The height of the water at the time of each observation was carefully marked, 

 and subsequently determined by the spirit level ; and the corresponding depth 

 upon the bar at Wheeling was simultaneously noted, so that all the discharges 

 might be computed with reference to the depth upon that bar. Due precau- 

 tion was observed to insure accuracy, by so adjusting the float that very little 

 surface should be exposed to the action of the wind — a source of error in such 

 observations exceedingly difficult to obviate. Finally, care was taken to put the 

 float in the thread of the channel, and to endeavor to select suitable weather 

 for each observation. 



