248 KEPORT — 1875. 



On the Bristol Joint Station. By Francis Fox, C.E. 



On a Steel Gradient Formation. By H. Handtside. 



On Bloclc-siynalling on Railways. By E. R. Harpee. 



On Improvements in the ClochvorJc of Revolving Lighthouses. 

 By J. HopKiKSON, D.Sc. 



Until recently tlie macliineiy driving tlie apparatus of revolving liglits lias 

 alwaj's been controlled by revohing fans, wliich slightly mask the variations of 

 friction in the machine and rollers which carry the light by adding a considerable 

 resistance of the air, which increases slowly with the velocity. A light thus 

 governed goes, at the best, if carefully regulated by the lightkeeper, too slow at 

 starting, whilst the lantern is cool and the lubricating oil thick, and too fast when 

 the apparatus has run some time. The lightkeepers endeavour to correct this ac- 

 celeration by taking off driving-weight. It is perhaps true that a careful man, 

 with the fan arrangement, or indeed' without any governor at all, by adjusting the 

 driving-weight, may keep his apparatus so near to time that there would be little 

 danger of niistake. " But it is undesirable that the want of such care should cause 

 such serious risks, if it can by any means be avoided. As a matter of discipline, 

 too, it is advantageous that a*n absolute rule maybe laid down that?;o sensible vari- 

 ation of velocity is permissible; and if it occurs, it should be only attributable to 

 interference with the machine, insufficient driving-weight, or neglect of winding 

 up, for either of which the lightkeeper is responsible. With fans it was necessary 

 that a certain error should be tolerated ; it is better that cmy error should con- 

 demn the lightkeeper. 



In the apparatus made at the works of Messrs. Chance during the last year, I 

 have replaced the fans by a centrifugal governor, in principle the same as those of 

 Sir "William Thomson and Mr. Grubb. It consists of a weight in the form of a 

 disk, sliding on a vertical revolving shaft, guided by feather keys. Two governor 

 balls, carried by arms which malce an angle of about 45° with the shaft, are con- 

 nected with the disk by links, so that in expanding they lift the disk from the collar 

 on which it rests when below speed. Two adjustable screws, tipped with leather, 

 are fixed to the frame of the clock above the outer rim of the disk. As soon as the 

 disk is lifted from the collar it comes in contact with these brake-screws. Since 

 the disk has a diameter of 12 to IG inches, and makes over a hundred revolutions 

 per minute, the friction has sufficient moment to control the rotation of the appa- 

 ratus. Indeed the clock goes at sensibly the same speed whether the apparatus, 

 weighing about a couple of tons, is in ge'ar or at rest. A little thumbscrew pressed 

 at pleasure against the edge of the disk serves to instantly stop the clock. With 

 the exception of Sir AVilliam Thomson's clock at the Holywood Bank, and those 

 arranged by Mr. Douglas for light-vessels, the clocks made by Messrs. Chance during 

 the last year are the only ones iii use for revolving lights capable of going_ any 

 thing like uniformly. This governor almost places it beyond the power of the light- 

 keeper to make his apparatus go wrong. Deficient weight he will be compelled 

 to correct; for the friction of the apparatus being constant, and the governor 

 not acting when below speed, the machine will slowly stop. 



In most lighthouse clocks, whilst the driving-weight is wound up, the motion of 

 the apparatus is either allowed to take care of itself, or is maintained by a weighted 

 lever acting on a ratchet-wheel, and spasmodically lifted by the act of winding. 

 With the fan-governor this must interfere with the rcgidarity of the motion, and 

 in any case it jerks the machine. The author finds it best to return to the oldest 

 maintaining arrangement, that of Huyghens, in which an endless chain or rope 

 passes over separate winding and driving pulleys, and hangs in two loops, of which 

 one passes under a snatch-block to which the weight is hung. The chain passes 

 continuously over the driving-pulley as it revolves. The author cannot understand 

 why this old and simple plan is not used for turret-clocks. With suitable pulleys, 

 and a chain of moderately accurate pitch, the clock works perfectly smoothly, and 

 is absolutely unaffected by the operation of winding. 



