246 REPORT — 1875. 



serve both purposes.) The loiver end of the rod is formed hoUo-w, .and receives one 

 end of a staff or baton of wood which rests on a bracket. The baton when put into 

 this socket cannot afterwards be withdrawn without being broken, as it is lield by 

 means of a spring catch, which is inaccessible so long as the baton remains whole. 



The action of the apparatus is asfolloius : — So long as the driver does not require to 

 pass within a danger-signal for protection the apparatus requires no attention. 

 When he finds this necessarj^, it is his duty to raise the vertical rod carrying the 

 baton, which is thereby removed from a position where it would be broken by 

 coming in contact with an arm of the "bell-crank" on the line. This action is 

 accompanied by a sounding of the whistle, which prevents the driver from keeping 

 the baton out of the normal position after passing the signal. It also gives the 

 necessary warning to signalmen and others that a train is approaching. Should a 

 driver inachertenihj pass a danger-signal, the baton, not having been moved into the 

 position of safety, must of necessity be broken at a point made specially weak. 

 The vertical rod being thus deprived of support falls, and by means of its con- 

 nexions causes the whistle to sound, at once giving warning of danger and recording 

 the driver's negligence. When a baton has been broken, the lower part of the ver- 

 tical rod protrudes from the tube in which it slides and allows the spring-catch to 

 become accessible, so that the part of the baton remaining in the socket can be 

 withdrawn and a new one substituted. The batons aa-e to be supplied to engine- 

 drivers at such a price as may be considered suiRcieut to secure the necessary vigi- 

 lance in preserving them. A simple and efficient way of preventing counterfeit 

 would be to place a seal on the weakened part. 



As usually constructed automatic signals act on ever}' occasion that a danger- 

 signal is passed. The effect of this is necessarily to induce reliance on the apparatus. 

 By the system which has been described, the driver has a certain duty to perform at 

 every danger-signal the neglect of which will subject him to pecuniary loss, and 

 also, if of frequent occiu-rence, to dismissal. There is therefore every reason to expect 

 that the vigilance of the driver would be fully maintained. 



The " block system " has now been ver}' extensively adopted, and the apparatus 

 used in connexion with it is being improved in order to eliminate the element of 

 human fallibility in so far as the operators are concerned. But if it is important to 

 get signals duly exhibited, it is equally important that they be attended to when 

 exhibited. It is therefore evident that the " block system " cannot work satis- 

 factorily so long as its efficiency depends exclusively upon the semaphore-signal, 

 which appeals to the sense of sight alone, and, especially when there is fog, is often 

 passed imnoticed by drivers. 



On tlie Trials of Screw Steani-Ships. 

 By William Denny, Leven SJiip-yard, Dumbarton. 



The object of this paper was to further the adoption of the progressive method 

 of trying steam-ships on the measured mile. 



The present method is, as a rule, confined to maximum power speeds, or to 

 speeds which are the maximum effects of half-boiler power. Such trials afford 

 only meagre and isolated results, giving little if any basis for the comparison of 

 different steamers, and they cannot, as they ought to, show the varying relations 

 of power and speed throughout the range of any steamer's possible speeds. 



The ratios of these relations are veiy unlike in different steamers, and a know- 

 ledge of them must be the basis of any true method of comparison. Mr. Froude's 

 resistance-curves, formed from model experiments, are a very good illustration of the 

 objects to be attained by progi-essive trials, which, when set off' on suitable scales, 

 should show at once the relation existing between any speed and power within 

 the limits of the experiments. 



For example, a vessel capable of such a series of speeds might be tried at or 

 about 13, 11, 9, 8, and .5 knots, the resulting mean speeds and developments of 

 power being set off and formed into a curve ; and it is very evident such a curve 

 would show more easily than any number of single trials the progressive difficulty 

 of driving the ship. 



