192 
however, be easily obtained. As it is not my purpose in this paper 
to ascertain absolutely the stability of any one boat, but merely to 
compare the stability of different forms of boats, I shall allow 
myself a great simplification. I shall treat the centre of gravity 
and centre of buoyancy of the midship section of a boat as if these 
were the centres of the whole boat. The other sections in each 
boat will present generally the same characteristics as the midship 
section, so that for purposes of comparison this method will be 
sufficiently accurate. The centre of gravity I shall take by 
estimation, after a consideration of the position of the different 
weights, the centre of budyancy I shall deduce from the form of 
the immersed part of the section. 
RowiInc Boats. 
Figure 3 represents a section of a well designed family 
rowing boat. G is the centre of gravity, the boat being supposed 
fairly loaded ; C the centre of buoyancy, the boat having from any 
cause received such a heel as is represented in the figure. AB is 
the arm of the righting couple. The power of the couple tending 
to right the boat will depend on the weight of the boat and the 
length of AB ; and, the weight of the boat remaining constant, 
the length of AB may engage our whole attention. Let us consider 
what is the effect on AB of heeling the boat gradually over. When 
the boat is upright, the position of C is, as I have said, directly 
under that of G, and AB vanishes. When the boat receives a 
slight heel, say to starboard, C moves out a little also to starboard. 
G dof not alter its position in the boat, but the vertical line 
through it falls a little to starboard of its original position, yet not 
so much as to pass through C._ A righting couple is thus produced, 
and it is evident that the length of the arm AB depends on the 
difference of the rate of shifting out to starboard of C, and of the 
vertical line through G. In all reasonably stable boats, C moves 
out much faster than the vertical line through G; hence as the 
boat hee’s over, the arm of the righting couple is lengthened, and 
its power increased. This process, however, will not continue for 
ever, Whena boat is very much inclined, the outward motion of C 
