RESISTANCE OF STEAM VESSEL WITH PLANE SURFACE. 75 



of construction, the use of which has been attended with complete success, in every instance 

 in which it has been tried. The advantages of iron vessels are stated to be, that they do not 

 weigh one-half that of a timber sea-going vessel, and they therefore draw considerably less 

 water, and give a greater speed with equal power ; greater safety, in consequence of being di- 

 vided into water-tight compartments by iron bulkheads ; and greater economy, as they do not 

 require so many repairs. The capacity is also increased for passengers and goods : a wooden 

 vessel of 30 feet beam is only 27 feet 6 inches inside, while an iron vessel would be 29 feet 

 6 inches ; consequently a saving of two feet is produced throughout the whole length 

 of the vessels. 



They besides possess the advantage in hot climates, of being cooler, more free from 

 vermin, and in consequence more healthy. In fact, the advantages seem to be generally ac- 

 knowledged. The only difficulty that has at present stood in the way of their employment, 

 in sea voyages, has been the effect of the iron on the compass : and this has been suc- 

 cessfully overcome in the late voyage of L'Egyptien to Alexandria ; in which the compass 

 was fixed under the direction of Professor Barlow, and has been found to work with the 

 same accuracy as in an ordinary vessel. 



We have no doubt, therefore, that iron vessels will in a short time become very general, 

 and add greatly to the facilities and extension of steam navigation. 



COMPARISON OF THE RESISTANCE OF A STEAM VESSEL WITH THAT 



OF A PLANE SURFACE. 



The resistance of vessels being a subject which has of late much engaged the attention of 

 engineers, we have been induced to add the following comparison of the resistance of a steam 

 vessel with that of the paddles, a calculation which can be arrived at with the aid of the 

 preceding experiments and investigations with considerable accuracy. 



Let V the velocity of the wheel, that of the vessel, s its sectional area immersed, and a 

 the area of a paddle whose action is horizontal and effect equal to the sum of all the paddles : 

 the resistance being as the square of the velocity, (V x>) 2 a will express the resistance on 

 the paddle, and i) 2 s would be the resistance of the vessel if it were a plane surface ; but the 

 real resistance being (V v)- a, the fraction of the resistance compared with a plane will be 

 (V vY a 

 v- s 



The value of a has been obtained by knowiag the depth of immersion, so as to ascertain the 

 angle at which the centre of pressure entered the water, and thence the number of times the 

 whole effective action exceeds that of the vertical paddle : this, multiplied into the area of the 

 paddle, gives the whole surface above denoted by a. 



In the following table is given the effective pressure exerted by the engines in every expe- 

 riment where the dip or immersion of the paddle is given ; but the comparison of the 

 resistance of the vessel with a plane is of course limited to those experiments only in which 

 the area of the immersed section could be ascertained. 



