342 ON PHYSICAL DATA 



translation of the vessel, and rotatory motion of the 

 screw, will be effective in giving the greatest 

 amount of motion of translation in the direction 

 of the vessel's motion. This relation would again 

 depend upon the resistance which the thread of 

 the screw met with in its progress through the 

 water. 



The third question has its application in the 

 conveyance of water through pipes, in order to 

 supply large towns with a quantity of water ade- 

 quate to their demands. 



The data required from actual observation in 

 order to give a solution to the above questions, 

 are of a very complex and intricate nature, and can 

 only be obtained by means of extensive experi- 

 ments, devised with great judgment, and well 

 conducted. The apparatus necessary for the 

 prosecution of such speculations, can only be 

 obtained at a great expense, which necessarily 

 prevents many, amongst the most earnest and 

 anxious enquirers, to know something of the 

 nature of those laws which operate in pro- 

 ducing such rapid and prodigious variations in the 

 material world, from pursuing their enquiries into 

 the more distan*-,and consequently less frequented, 



