WATER AND WATER NAVIGATION. 81 
Atlantic, appears to be about as follows :—iff, fpeed; 
2n d^fafety; 3rd, comfort of tobacco-fmokers. 
The contad-fridion 1 of the water and fldes of the 
veflel appears to be left to take care of itfelf; and yet 
Nature very carefully provides a well-lubricated furface 
for her fwimmers with means for a continuous lubrication. 
May it not be that the faving in coals would pay for the 
coft of oil, or lubricator ? The extra fpeed being fo much 
clear gain. 
The propelling power of fifhes depends upon convo¬ 
lutions: the convolutions being lubricated, adjuftible, 
flexible, inclined planes, capable of tranfmitting, prac¬ 
tically, the whole of the motive-power for reading againft 
the water-fulcrum. A very different affair from <c fcrew- 
propellers.” 
On the fcrew I cannot do better than quote again 
from Pettigrew. At pp. 152,153 he writes as follows:— 
“ In the ordinary fcrew the blades follow each other in 
rapid fucceflion, fo that they travel over nearly the fame 
particles (whether water or air) in nearly the fame interval 
of time. * * * If the fcrew employed in navigation 
1 The late Thomas Winans, of Baltimore, M d -> U.S.A., fhowed me, fome 
twenty-five years ago, the tabulated refixlts of his numerous experiments (fome 
thoufands, I think) on the fridtion produced by the paflage of veflels through 
the waters, and its effedt on the power of the fhip; and the refults were amaz¬ 
ing ; Mr. Winans remarking, that in his judgment too little attention had been 
paid to this point. But his ideas, like thofe of naval architedts, for leflening fuch 
fridtion, were confined to model: to leaving the water on lines as fiiarp as the 
entering ones. 
