ON THE GENERAL THEORY OF THE STEAM ENGINE. 



201 



are very numerous and of a varied character, were conducted with great care ; and an interesting 

 description of the circumstances under which they were made, and a well-arranged table 

 showing the results observed, are given in detail in vol. i. of the Transactions of the Institution 

 of Civil Engineers, to which we refer such of our readers as may wish for minute information. 

 A few extracts will be sufficient to show that the theory which considered the resistance of a 

 vessel moving on a canal to be as the square of the velocity, can no longer be maintained. 



The canals upon which Mr. Macneill made his experiments were of very different sizes. 

 This circumstance alone had the unexpected effect of destroying the universality of the 

 application of the ordinary rule. On neither canal did the resistance vary precisely as the 

 square of the velocity : and it is remarkable that the increase was not the same in the wide 

 and deep canal as it was in the narrow and shallow one. An extensive field of enquiry is thus 

 opened, which will require much time and numerous observers to collect the harvest of 

 interesting and important facts which it contains. 



We have thrown our extracts into Tables, for more convenient reference and comparison. 

 Table I. contains the experiments on the larger canal: Table II. those on the smaller; and 

 it will be observed that the resistance on this canal was less at velocities of 9 and 10 miles 

 per hour, than of those of 7 and 8 ! The velocities marked * were taken as the standards of 

 comparison. 



TABIE I. EXTRACT. EXPERIMENTS MADE UPON THE FORTH AND CLYDE CANAL. 



Dimensions of the Section of the Forth and Clyde Canal. 



