INTRODUCTION. XXX111 



The centre of gravity of the whole body, and that of 

 the part immersed, must occur in the same vertical line, or 

 the line of pressure and the line of support must coincide; 

 and, secondly, that the magnitude of the body is to that of 

 the part immersed below the plane of floatation, as the 

 specific gravity of the fluid is to that of the floating body. 



Of the truth of the doctrine which is here propounded, and, 

 let us hope, satisfactorily demonstrated in the sequel of our 

 work, we have a curious illustration afforded by an Arab ship- 

 builder in Java, whose task is thus described in GEORGE 

 EARL'S Eastern Seas: "The largest merchant vessel in Java, 

 a ship about 1,000 tons burden, was built by an Arab merchant, 

 in a long but shallow river, which runs into the sea near Soura- 

 baya. As great expense is incurred by floating the timber in 

 rafts down the river, he determined to commence the work in 

 the forest itself, as he would thereby be enabled to select the 

 best trees for the purpose. He accordingly ascended the river, 

 accompanied by a sufficient number of workmen, conveying the 

 necessary materials, and commenced the undertaking about 80 

 miles from the sea. When the keel and the floor timbers were 

 laid, and a few of the bottom planks nailed on, he launched the 

 embryo vessel, and floated her gently down the river to a place 

 in which the water was deeper. Here the building was con- 

 tinued, until it became necessary to seek a deeper channel, and 

 in this manner the work proceeded, the vessel being floated 

 further down the river, whenever the water was found to be too 

 shallow for her to float, until at length, she was fairly launched, 

 half finished, into the sea, and completed in the harbour." 



The operations of this ingenious orientalist proceeded upon 

 the truth stated in Inference 5, page 261, that if a body float 

 in equilibrio on the surface of a given fluid, and if the part 

 below the plane of floatation be increased or diminished by a 

 given quantity, the absolute weight of the body, (in order that 

 the equilibrium might still obtain,) must be increased or dimi- 

 nished by a weight which is equal to the weight of the portion 

 of the fluid that is more or less displaced, in consequence of 

 increasing or diminishing the immersed part of the body, or 

 that which falls below the plane of floatation. 



