STABILITY^ PROPULSION, AND SEA-GOING QUALITIES OF SHIPS. 25 



cube of the lineal dimeusions. This would foUow from the theory of the 

 resistance of submerged bodies, on the supposition that the resistance varies 

 as the square of the speed. If, again, we consider Mr. Scott llussell's theory 

 of the length of ships (that their extreme speed should not exceed that of 

 an oscillating wave, bearing a definite ratio of length to that of the ship), we 

 arrive at the same conclusion, the length of the wave varying as the velocity 

 squared. 



Proposed Experiments. 



The experiments upon resistance which we consider most important to be 

 made are these : — 



That a ship of considerable size and fine form should be carefully selected ; 

 a screw steam-sliip, with a screw capable of being lifted, with a clear deck, 

 offering no unnecessary resistance to the air, and with little or no rigging. 



That her form should be carefully measured in dock (her lines taken off, 

 as it is technically called), and sight-marks carefully laid down, so as to 

 ascertain whether she deforms in any way when afloat. 



That she should be towed at various speeds, from the slowest that can be 

 rated to the fastest that can be obtained ; and that the resistance should be 

 ascertained by a traction-dynamometer, self-recording. 



That the place selected for the experiments should be a deep inland water, 

 free from ground-swell, and such that the speed of the ship can be observed 

 from the land as well as from the vessel. The water also should be clear 

 enough to admit of being seen through to a considerable depth. The place, 

 if tidal at aU, should be free from cross tides or irregular currents. These 

 conditions, it is believed, may be found both in Norway and on the west 

 coast of Scotland. 



Careful observations should also be made with a view to ascertain the 

 direction and velocity of the local currents caused by the ship's motion. 

 "WTiat these should be will demand careful consideration, having regard both 

 to the ship and to the place selected, and to the personnel of the observers. 



The same remarks will apply to the precautions necessary to i)revent 

 interference by the currents thrown back by the towing-vessel or vessels, 

 and to eliminate other sources of error. It is of especial importance that the 

 ship which is being towed should be kept clear of the wake of the towing- 

 vessel or vessels. It might be necessary for this purpose to have two tug- 

 boats with hawsers meeting at an angle in the form of the letter Y. 



It is desirable that these experiments should be performed with at least 

 two vessels considerably differing both in size and proportions, and, for each 

 of them, with different condition as regards smoothness of surface. 



A third class of experiments should also be made to determine the rate of 

 retardation of a vessel which has been made to attain a certain velocity, and 

 then (the propelling-power suddenly ceasing to act upon her) is allowed to 

 come gradually to rest through the resistance of the water. 



It would be desirable that the same vessels (and as nearly as possible 

 under similar conditions of draught and trim) should be made use of for 

 trials of propulsion, and that in these, again, a dynamometer should be 

 interposed between the engine and the propeller ; and in this case also the 

 local currents and waves due to the joint disturbance of ship and propeller 

 shoidd be observed. 



We consider that experiments of the kinds which we have proposed have 

 now become necessary, not only to the theory of resistance, but also to the 

 practical calculations of the effect of steering- and propelling-aijparatus, and 



