204 APPENDIX. 



a fluid we have no reason to suppose that the head pressure is at all changed. That it is so, 

 is clearly made out by the valuable experiments of the late Colonel Beaufoy, in which bodies 

 of various mathematical forms are employed, and which distinctly point out the separate 

 effects produced by altering the velocity, the figure of the head, and the figure of the stern. 

 A volume of these experiments, elegantly executed, has recently been presented, in the most 

 liberal and handsome manner, to his scientific countrymen, by Henry Beaufoy. At page xxxix 

 of the Introduction, the different forces which act upon a body moving through a fluid are 

 clearly defined as follows : l 



" By HEAD PRESSURE, is meant the total pressure which exists against the head end, or 

 " foremost part, of a body immersed, either wholly or in part, in any given fluid when such 

 " body is at rest. 



" By STERN PRESSURE, is meant the total pressure which exists against the stern end, or 

 " hindermost part of a body, immersed, either wholly or in part, in any given fluid when such 

 " body is at rest. 



" By PLUS PRESSURE, is meant the additional pressure which is sustained by the head 

 " end, or foremost part of a body, moved through a fluid ; which additional pressure is over 

 " and above what we have termed the Head Pressure, and arises from the fluid being obliged 

 " to be displaced in order to permit the moving body to pass through it. 



" By MINUS PRESSURE, is meant a subtraction of pressure from the stern pressure, and 

 " which subtraction is occasioned by the fluid not pressing so strongly against the stern end, 

 " or hindermost parts of a body, when such body is in motion through the fluid, as when the 

 " body is at rest. 



" By FRICTION, (as relating to this subject,) is meant that sort of resistance to a body 

 " moved through a fluid, which arises either from the adhesion of the particles of the fluid to 

 " the surface of the moving body, or from the roughness of the body ; or from both these 

 " causes united. 



" By TOTAL RESISTANCE, is meant the sum total of the plus pressure, the minus pressure 

 " and friction united." 



To complete the forces which act on the body we should introduce two other classes, viz., 

 those which arise from the destruction of the equilibrium of pressure caused by the dis- 

 placement and consequent unevenness of the fluid, and those which arise from the inclination 

 of the axis of the moving body : these may probably account for many of the discrepancies 

 observed in the results of the experiments. 



Colonel Beaufoy's extensive experiments, taken in connexion with those of Macneill and 

 Russell, supply various important data for the sciences of hydraulics and naval architecture. 

 These subjects have, unfortunately, been but little cultivated by British mathematicians, 

 notwithstanding their peculiar importance to this country ; and we regret that time will not 

 allow us to enter here into any discussion of what has already been done. We trust, however, 

 that the theories of waves and naval architecture will shortly be taken up by some enterprising 

 and able analyst, who may allow his attention to be drawn to such pursuits by their vast 

 utility and importance. 



1 These definitions were drawn out by the late Earl Stanhope. 



