Intelligence and Miscellaneous Articles. 223 



external to the system, which need be considered, are the pressures 

 of the water on the blades of the two oars and the resistance of the 

 water to the motion of the boat. If the boat be on the point of 

 moving, these forces must equilibrate each other, and as they 

 are parallel, the semi-resistance of the water to the motion must be 

 equal and opposite to the pressure on the blade of one oar. Again, 

 for the equilibrium of this oar, the moments round the rowlock of 

 the pull exerted by the rower and of the pressure against the blade 

 must be equal and opposite. Hence the moments round the row- 

 lock of the pull of the rower, and of a force equal to the semi- 

 resistance of the water to the motion, supposed to act at the blade 

 of the oar, must be equal. 



This is the proposition which Mr. Abbott seeks to establish, and 

 which he has, I think, paradoxically, if not inaccurately, expressed 

 by stating that the oar is a lever of the first order. 



The word lever has a kineinatical reference, and implies a rigid 

 body having a fixed point. The division of levers iuto different 

 orders is an obscure way of stating the relative position of the 

 fixed point, and of two forces which are supposed to act upon the 

 body. 



Xow in the case of the oar, the fixed point is the blade, and the 

 resistance of: the water to the motion of the boat does not act on 

 the oar at all. To say, then, that the oar is a lever of the first order 

 acted on by the pull of the rower and the semi-resistance of the 

 water to the motion of the boat applied at the blade of the oar, the 

 rowlock being the fulcrum, cannot be regarded as accurate, except 

 we look upon the rower, not as moving on the boat, but as moving 

 back the world. 



The investigation of the question, regarding the oar as a lever 

 whose fixed poiut is the blade, can be easily accomplished. 



Let P be the pull of the rower, E the reaction between the oar 

 and the boat at the rowlock, 8 the semi-resistance of the water to 

 the motion of the boat, and a and b the distances of the rowlock 

 from the hand of the rower and the blade of the oar. 



We have then, from the equilibrium of the oar, 



P(a + 6)=E6 (1) 



Again, as the boat is just about to move, the forces acting on it 

 equilibrate each other, and these are 2S, 2E, and a force equal and 

 opposite to 2P, exerted by the feet and body of the rower against 

 the boat. As these forces are parallel, we have S-|-P = E. Sub- 

 stituting for E in (1) and reducing, we get 



P« = S6; 

 the same result as before. 



OX THE SPECIFIC HEATS OF THE VAPOURS OF ACETIC ACID AND 

 NITROGEN TETROXIDE. 



To the Editors of the Philosophical Magazine and Journal. 

 GrENTLEMEff, 



Amongst others, it has lately been my business to read a very 



