154 History of' Mecluinical Inventions and 



New Scheme by Kirbing of Stone. 



To 12 lbs of Welsh Bar of Wrought-Iron of dimensions as 

 per Sketch in a yard, or including botli sides together, with 

 the cross T, and bolt at every four feet in length, which, al- 

 though it requires no labour, but only welding the T at every 

 four feet, and the quoted prices at present are only 14s., I 

 have here estimated at double that, viz. 28s. per cwt- or 3d. 

 per lb. - - - - - - 3 



To Granite Kirbing, delivered in London, for both sides, 

 at 4s. 6d. per yard, - - - 



To Boring and Setting, at 5d. per yard, 



Difference in favour of Kirbing per yard, - - 6 



There are no doubt many districts, through which roads may have to 

 pass, where hard, strong, durable stone may be procured, which would 

 render this plan still cheaper, as the stones only require to be straighted 

 on the top, and one edge, with square joints, and the bottoms blocked work, 

 and may be in length one foot six inches to three or four feet. 



In districts of the country where strong durable stone cannot be reason- 

 ably procured, it may be advisable to give a greater body of stone, and cut 

 a groove an inch deep for the flanch of the waggon-wheel, and fix the bar 

 of iron in the middle of the stone ; but this will not be necessary when 

 granite, or good whin-stone, or limestone can be procured, as they will 

 be sufficiently strong on the edges, agreeable to annexed sketch. 



I am, Sir, respectfully, 



Your obedient servant, 

 Aberdeen, 14</t February 1825. John Gibb. 



6. Description of a Single Valve Sluice, invented by Robert Thom, 



Esq. Rothesay. 



The construction of this sluice (Plate I. Fig. 9,) is partly similar to 

 that described in our last Number ; but it is applicable to cases where 

 the reservoir is on high grounds above the works requiring the water, 

 and where, of course, the water passes down a declivity. 



AB, part of the tunnel of a reservoir. 



B, a sluice that turns upon pivots a little above its centre of pressure- 



CD, The rivulet that carries the water from the reservoir down to FG, 

 part of a level canal or aqueduct. 



EH, a hollow cylinder. 



KL, a cylinder, water proof, of rather less specific gravity than water, 

 which moves freely up and down within cylinder EH. 



M, a pulley. BMK, a chain, &c. 



I, a small cistern, kept always full of water by the waste from the 

 sluice, or by a small hole in it. 



HI, a small pipe, communicating between cistern I and cylinder EH. 



