1819.] 



THE CIVIL ENGINEER ANU ARCHITECT'S JOURNAL. 



309 



communicating an equal motion to the two weights A, and B; an 

 equal force must therefore be distributed throuffh the three weights 

 A, B, and C, and that force can only come from the gravitating 

 force of the latter (C), this force being that with which it would 

 actually descend if left to itself. If A, and B, he each 10, and C =r 

 1, then the mass through which the force is diffused will be equal 

 to 21 times the weight of C. The force actually existing in each 

 portion of the mass is therefore the 21th part of what it was in 

 each portion of the added weight C, and will in this combination 

 descend witli the 21th part of the velocity that it would do if it 

 descended freel)', tliat is, the 21th part of the ordinary effect of 

 gravity. Having thus endeavoured to explain the principle upon 

 which tlie furnace rarefaction proceeds, let us now further illus- 

 trate it. 



Fig. 1. — Sectional Elevation, 



Fig. 2.- Plan. 



Suppose 900 feet in B, and 730 in A, represent the weights A, 

 and B, balancing each other, and 170 the weight C, with a fall 

 of 900 feet, the velocity acquired thereby when falling freely 

 is theoretically 240 feet per second; but 170 is the lO'tith part of 

 1800 (the sum of 900, 730, and 170), consequently 210 divided by 

 10-6 gives us 22-7 feet per second for the real velocity in the 

 upcast-shaft. 



Thus we have an approximation at least to the velocity of the 

 air in the two shafts; but which is after all of little practical use 

 or application; for, the direct opening between the shaft being 

 closed, the weight C, 170 (which in the supposed case is equal to 

 12-5 lb. upon the square foot) immediately becomes a gravitating 

 force descending with more or less velocity as it is enabled to 

 propel the air through the workings of the colliery; and, taking 

 12-5 as the first mover or cause, we may look for 9 as the mechani- 

 cal effect in moving the air through all the air-courses of the col- 

 liery, and ultimately discharging it through the upcast-shaft into 

 tlie atmosphere; and though it is impracticable to balance the 



account by estimating the actual weight of air in the colliery, the 

 different velocities with which it is propelled, together with the 

 amount of retardations, whicli if obtained would accurately express 

 the force applied, yet the aggregate may be satisfactorily ascer- 

 tained by the application of the water-gauge to any single partition 

 or door which stops the direct passage of the air between the 

 shafts, and constrains it to take the circuit of the colliery work- 

 ings; that is, wliere the downcast and upcast shafts are contiguous, 

 and one side of the door is directly and freely connected with the 

 influent current from the bottom of the downcast, and the other 

 side similarly connected with the effluent current as it enters the 

 iipcast, the difference of the height of the water in tlie tubes of 

 the gauge will expi'ess the force applied to maintain the current 

 between the bottom of the t« o shafts passing through the work- 

 ings of the colliery anali>gous to the amount of force required to 

 draw a long rope through a winding passage. 



Mr. Brunton next described the mechanical means of the ven- 

 tilator he has erected for Thomas Powell, Esq., of the Gaer, near 

 Newport, Monmouthshire, upon one of his collieries, and the par- 

 ticular advantages it possesses over the furnace as a ventilator. 

 Over or near to the upcast shaft is constructed a hollow drum, with 

 curvilinear compartments, thi-ough which the air is discharged 

 with that degree of force due to the velocity with which the drum 

 revolves upon its axis. The diagrams figs. 1, and 2, represent a 

 plan and elevation of the ventilator. A, is a drum, 22 feet e.xterior 

 diameter, with curvilinear compartments B, IG feet mean dia- 

 meter; C, is a steam-engine to give motion to the ventilator, the 

 centrifugal force of wliich at 120 revolutions per minute will be 

 39-23, wliich, multiplied by the weight of 6 cubic feet of air = 

 4^ of a pound, will give a pressuie'of 17-5 pounds on the square 

 foot, as the amount of rarefaction produced in the interior of the 

 drum, and consequently in the upcast shaft with which it is con- 

 nected (by D, the air culvert), which is much beyond what can be 

 obtained by the furnace, yet greatly within the limits of the capa- 

 bility of this machine, as shown below. The amount of rarefac- 

 tion is governed by the speed of the engine, and is also under con- 

 stant and visible inspection by a water or mercurial gauge: thus 

 when the drum revolves 



CO times per minute the rarefaction Is 4-3 lb. on squart foot. 

 ao „ „ » 7 „ 



l-'O „ „ 17-3 „ 



1-50 „ „ 2r-o „ 



IHO „ „ 3'.)0 „ 



210 „ „ 630 „ 



In order better to understand the peculiar self-adaptation of 

 this apparatus to all the circumstances that present themselves in 

 the ventilation of collieries, let us suppose it altogether uncon- 

 nected with any length of air-course, the air from the atmosphere 

 having free access to the centre, and space for free discharge from 

 the circumference, and a velocity given to it of 150 revolutions 

 per minute, creating a rarefaction of 27 lb. ])er square foot in the 

 middle of the drum; then the velocity of tlie air through the 

 machine would be 108 feet per second, and the aggregate amount- 

 ing to 8+24. cubic feet per second, or 505'440 per minute. 



Then let us suppose a state the very reverse of the above — viz., 

 that no air be permitted to enter the drum at the centre part, of 

 course none can be discharged at the circumference; therefore, 

 there being no resistance to the motion of the drum from discharge 

 of air through the curvilinear compartments, but the power of the 

 engine continuing the same, is consequently expended in increasing 

 the velocity of the drum, and thereby the rarefaction. In the 

 former case the effect is exhibited in the discharge of air; in the 

 latter by the degree of rarefaction maintained in the middl* of the 

 drum. 



From consideration of these two cases, it is manifest that the 

 power required to work the machine will be as the quantity of air 

 ascending the upcast-shaft, and the amount of rarefaction required 

 to draw i"t through the colliery; and such is the principle of self- 

 adjustment of this apparatus, that if from any cause a less quantity 

 of air is passed through the colliery at one time than anotlier, the 

 engine (always exerting the same power) will of its own accord 

 accelerate the velocity of the drum and increase tlie rarefaction, 

 for, the power applied being the same, the effect will be commen- 

 surate in tlie quantity of air discharged, the amount of rarefaction 

 attained, or both combined. 



The machine is an entirely new modification of the fan. Its 

 construction is of tlie most simple integral character; it has no 

 valves or separate moving parts; has no attrition, and all the 

 friction is resolved into a foot pivot moving in oil; when at rest 

 offers no impediment to air ascending from the shaft, is very inex- 

 pensive, and liable to no deranaement; in short, it is a simple me- 

 chanical implement, whereby any degree of rarefaction necessary 



