TRANSACTIONS OF THE SECTIONS. 147 



was about two-tliirds that of copper, and the electro-chemical action upon it was 

 not only so slow as not to exceed the action of salt water upon the copper sheath- 

 ing on a wooden vessel, hut this action it was possible to control within certain 

 limits. These results have been confirmed by careful experiments made under the 

 dii'ection of the Admiralty at Portsmouth, where zinc-sheathed ii-ou plates had 

 been submerged for eighteen months, and had been taken up bright and clear of 

 any kind of fouling whatevei*. The method had been invented and patented by 

 Mr. T. B. Daft, C.E., who had also devised a plan for the construction of iron ships, 

 by which, instead of close-fitting butt-joints, the plates were lap-jointed on to a 

 back strap, with an intervening space of about au inch wide, which was filled 

 with a caulking of compressed teak, into which the nails were driven for fastening 

 the zinc sheathing to the hull of the ship. By this plan of construction a flush 

 surface was obtained, while the strength of the ship would be increased, and as 

 fouling woidd be entirely prevented by the zinc sheathing, iron ships could here- 

 after be sent on the longest voyages. One of the commercial results of this appli- 

 cation of that sheathing would therefore be the doubling of the iron ship-building 

 trade through the demand for iron instead of wooden sailins--vessels. 



On the Treatment of melted Cast Iron and its Conversion into Iron and 

 and Steel by the Pneumatic Process. By E. Mtishet. 



On the Theory of the Influence of Friction upon the MecJianical Efficiency of 

 Steam. By Prof. W. J. Macqtjoen Rankine, LL.B., F.E.SS. L. ^- E. 



The results arrived at by the author of this paper are based on the following 

 principle. Let W be the indicated work of a given quantity of steam, without 

 deducting loss by friction, and H the mechanical equivalent of the expenditm-e of 

 heat required in order to do that work ; so that W-f-H is the efficiency of the 

 .steam without friction. Let F be the quantity of work lost through fiiction in the 

 cylinder; and let the heat produced by that friction be wholly taken up by the steam. 

 Then the work done is diminished to W — F, and the heat expended is diminished 



to H — F ; so that the efficiency becomes ~ ,. The special way in which the 



H — F 

 friction takes effect in ordinary steam-engines is by diminishing the expenditure 

 of heat required for the prevention of liquefaction in the cylinder. 



Remarks on the Experiments of the Committee npon the Resistance of Water 

 to Floating and Immersed Bodies, By Prof. W. J. Macquorn Rankine, 

 LL.D., F.E.SS. L. 4- E. 



The author said that his object in reading the present paper was not so much to 

 bring forward an}- opinions of Iiis own as to open the way for a discussion on the 

 •subject of the resistance of water to bodies passing through it. The custom of the 

 Association was that a Report shoidd be discussed ; and, therefore, when it was 

 desired to hold a discussion on the subject of a Report, it became necessary to read 

 a commimication from some individual on the same subject. With respect to 

 the experiments recorded in the Report, he would observe that they formed a body 

 of facts which were available for every inqiurer to reduce in his own way. From 

 a brief investigation of their results, by the aid of graphic projection, he believed 

 that the following conclusions might safely be di'awn :— 



1. That agreeably to what was previously known as to the resistance of water to 

 the motions of bodies of small dimensions at low speeds, the resistance increased, 

 on the whole, somewhat more slowly than the square of the velocity. 



2. That when the velocitj' went beyond the maximum velocity suited to the 

 length, according to Mr. Scott Russell's rule (that is to say, about 3| ft. per second, 

 the models being 4 ft. long), the resistance showed a tendency to increase at a 

 rnoro rapid rate, and the water became so much disturbed by waves as to make it 

 difficult, and sometimes impracticable, to continue the experiments. 



3. That while the midship section of model A was to that of model B as 1-57 



10* 



