APPLICABLE TO MATHEMATICS, &C. 341 



translation, of all rigid bodies, is affected by the 

 resistance which the fluid opposes to their pro- 

 gress. The second question is one closely con- 

 nected with the naval architecture of this srreat 

 country, since vessels are supported in two fluids, 

 water and air, whose specific gravities are as 1 to 

 855. Instead of vessels being urged by means of 

 the currents of winds, the effects of which being 

 collected by means of strong canvass to a certain 

 point, it is now becoming customary to urge them 

 on by means of the screw propeller, which acts 

 on the vessels at a point very different from the 

 resulting accumulation of atmospheric currents. 

 "With respect to the screw propeller, there have 

 been numerous experiments made, some by 

 private individuals, and others by the govern- 

 ment, in order to ascertain, if possible, the best 

 form of screw for propelling the vessel through 

 the water with the greatest possible velocity. 

 Inquiries of this nature ultimately led our ingeni- 

 ous associate. Professor Woodroft, to invent and 

 adopt a screw with a varying pitch, which has 

 succeeded much better than the screw with a 

 constant one, in effecting the object for which 

 it is proposed. 



There is little doubt but the relative motion of 



