242 report — 1859. 



is produced on the rudder's surface ; and when the wind is abaft, the same sail being 

 full, a greater speed may be given to the screw in order to make its oblique action 

 stronger and let the ship turn quicker. In the intermediate positions between the 

 head and the back wind, the main-top sail is directed in such a manner that it is 

 always acting against the screw. These manoeuvres of screw ships have been exe- 

 cuted several times, and have enabled ships to enter crowded roads and to pass 

 through spaces where ordinarily it would have been impossible to pass. 



Ships are sometimes required to remain in one position without dropping anchor ; 

 with sails, as with paddles, there is always lee way, and the ship cannot keep the 

 same position unless with a beam wind. It is also difficult to take another ship in 

 tow, as large ships want much time to send their heavy tow ropes on board, and have 

 generally to drop anchor and weigh again when the second one is in tow ; this is a 

 very long operation, and may be readily avoided by making use of the properties of 

 the screw when the wind is ahead or astern. Suppose, for instance, that a ship is 

 intending to take in tow another lying at anchor. She will sheet and hoist her mizen- 

 top sail and gallant sail according to the wind, and place herself a short distance ahead 

 of the other, and make her engine work slowly. Thus as the backing force of the 

 mizen sails would be compensated by the heading force of the propeller, the ship 

 acted on by these two equalized and opposite forces will be motionless, but she will 

 steer as well as if making way, on account of the artificial current before alluded to, 

 and may change her direction or remain quite motionless, regardless of the direction 

 of her head, as long as may be desired. This I have done several times when ordered 

 to take ships in tow, and once remained nearly twenty minutes in almost exactly the 

 same position. 



This combination of both propelling powers, the sails and the screw, may also be 

 used to maintain the ships with an oblique direction of the wind, two or three points, 

 for example, by bracing properly the mizen-top sail ; but when there is a slight lee 

 way, and if the wind blows in the direction of the beam, it is the common condition 

 of sailing or paddle vessels standing on. 



Condensed Abstract of a First Set of Experiments, by Messrs. Robert Napier 

 and Sons, on the Strength of Wrought Iron and Steel. By W. J. Mac- 

 quorn Rankine, C.E., LL.D., F.R.SS. L. fy E. 



The experiments to which this abstract relates form the first set of a long series 

 now in progress by Messrs. Robert Napier and Sons, the details being conducted by 

 their assistant, Mr. Kirkcaldy. The whole results are now in the course of being 

 printed in extenso, for publication in the 'Transactions of the Institution of Engineers 

 in Scotland' for the session 1858-50*. 



The present abstract is all that it has been found practicable to prepare in time for 

 the meeting of the British Association ; and, notwithstanding its brevity and extreme 

 condensation, it is believed that the results which it shows will be found of interest 

 and importance. It gives the tenacity and the ultimate extension, when on the point 

 of being torn asunder, of the strongest and the weakest kinds of iron and steel from 

 each of the districts mentioned. Each result is the mean of four experiments at least, 

 and sometimes of many more. 



The detailed tables, now being printed, will show many more particulars, and 

 especially the contraction of the bars in transverse area along their length generally, 

 owing to "drawing out," and the still greater contraction at the point of fracture. 

 The experiments now complete were all made with loads applied gradually. Experi- 

 ments on the effect of suddenly applied loads are in progress. 



Iron Bars. 



Tenacity in lbs. Ultimate extension in 



per sq. inch. decimals of length. 



Yorkshire: strongest 62886 0'256 



weakest 60075 0-205 



(forged) 66392 0-202 



* This volume of ' Transactions ' has since been published. 



