24 Mr G. R. Blackwell on the 



in the immediate vicinity of Black Rock, enabled him, 

 with his zeal for the accomplishment of this object, to 

 devote much time to completing an exact survey. By 

 reference to Mr Blackwall's elegant map of a section of 

 Niagara River opposite Black Rock, it will be observed that 

 thirty-eight soundings were taken in three distinct ranges or 

 lines across the channel of the river, each of the ranges being 

 at the distance of six hundred and sixty feet apart.* After 

 thus obtaining three cross sections of the volume of the cur- 

 rent, whereby its area or dimensions were ascertained, the 

 velocity of the surface was then found in ten different places 

 between these three lines, by noting the time in which float- 

 ing bodies set adrift in different parts of the width of the 

 river, were borne down from one sectional line below it. All 

 these admeasurements were made with every attention to 

 accuracy. 



Having thus found by experiment the velocity of the surface 

 of the stream, the average or mean velocity of the bottom and 

 middle, as well as of the surface, was ascertained by means of 

 the formula established by Eytelwein (v = ~ x 9), which for 

 measuring the volume of water flowing in rivers of great depth, 

 I consider to be a closer approximation to accuracy than those 

 established by Prony and other philosophers, who have inves- 

 tigated the subject of the discharge of water flowing down the 

 inclined planes of the beds of rivers. These calculations have 

 been carefully revised ; and the results stated may, therefore, 

 be deemed as a sufliciently accurate estimate of the volume 

 of water that flows down from Lake Erie. 



Allowing about 374,000 cubic feet of water (by estimate) 

 to flow through the harbour of Black Rock per second, as in- 

 dicated on the map, the results of their calculations shew that 

 about 22,440,000 cubic feet, or 167,862,420 gallons, weighing 

 710,250 tons, or 1,402,500,000 lbs. of water flow out of Lake 



* In Mr Blackwall's map the left hand column of figures in each section 

 represents the distance of each sounding from the American shore, and 

 the right hand column the depth of the soundings. The distance of the 

 soundings from each other may be found by subtracting each measure- 

 ment from the one next above it. The arrow denotes both the direction 

 of the current and the point of compass. 



