196 MAN-ENGINE 



these together cable laid. In the timbers, grooves are cut of such dimensions that 

 the screw bolts may have the effect of so pressing the timbers together, that the 

 ropes are held in place by the friction thus induced. The length of those timbers is 

 4$ fathoms ; this great length is a consequence of local circumstances. 



The rope diminishes gradually, viz., four wires less for each 50 fathoms descent. 

 The estimate of the strength required was made thus : 



Ibs. 



1. The weight of the rope 5,600 



2. Weight of steps and handles, &c 2,200 



3. Weight of 50 men 7,500 



4. 185 fathoms of deal and 90 fa thorns slide-bar . . 6,795 



22,095 



And assuming that the double rope of 36 wires would bear, at the utmost, 

 2 x 36 x 1,100 Ibs. = 79,200 Ibs., the load of 22,095 Ibs. would be 28 per cent, of the 

 ultimate strength. 



For safety in case of the accident of the power-ladder breaking, several good 

 arrangements have been adopted, so that any serious accident is not likely to 

 occur, should even a side of the power-ladder give way. At several parts of the 

 length, the two sides of the ladder are connected together by a very strong chain ; 

 this chain passes over a fixed pulley ; and it is evident that, if on either side the ladder 

 were to break above this, its fall, if not entirely checked, would be very much 

 broken by the counterbalancing weight of the other side, acting by means of the 

 chain. 



Again, at various stages there are wedge-shaped blocks attached to the planks, in 

 which are fixed the friction pieces, and these wedges would fall into wedge-shaped 

 bearings, that are secured by timbering in the shaft, and so, having broken at any 

 point above these, the fall is limited to 7 feet at the utmost. 



In conclusion, it may be mentioned that in order to ascertain the exact state of the 

 wires, several pieces of the rope have been kept exposed in different parts of the shaft; 

 these are from time to time examined, but since 1837, when the power-ladder of 

 iron wire was erected in Andreasberg, the progress has been so very slow, that little 

 is to be apprehended from the effects of rust, so long as care is taken to keep the 

 ropes properly tarred. 



The total cost of one side was 607 Prussian thalers, and therefore the total cost 

 of power-ladder was 1,214 thalers = 1 821. 10s. 



The mines in Cornwall being as deep as those in the Hartz, it became a question of 

 moment to adopt some machine for ths relief of the miner in that county. Medical 

 men had long expressed their conviction that much of the lung disease prevalent 

 amongst the men working in the deep mines of the Gwennap district was due to the 

 violent exertion of climbing on perpendicular ladders from a depth varying from 200 

 to upwards of 300 fathoms. At length the subject was taken up by the Royal Corn- 

 wall Polytechnic Society, and a man-engine was introduced, which in most respects 

 resembled the German power-ladders. 



The following is a short account of the principal phases of its introduction, due 

 entirely to the ready and generous initiative taken by the Polytechnic Society : 



At the first general meeting of the society in 1834 Mr. Charles Fox offered three 

 prizes for the perfection of the means then in use for the descent and the ascen- 

 sion of miners. The first project was that of Michael Loam the engineer, the same 

 who afterwards constructed the machine at Tresavean. The competition remained 

 open for many years; several plans wore produced, and the prizes awarded. In 

 1838 Mr. Fox offered 1001. to the first mine that would make a trial in the desired 

 way ; this example was followed by other individuals, and the sum of 530/. was 

 put into the hands of a committee, who were charged with sending circulars to 

 the mines. The adventurers of Tresavean accepted the proposed conditions, and in 

 January 1842, two rods moving alternately, conducted by an hydraulic wheel, were 

 working to a depth of 26 fathoms. The steps were 12 feet distant from eacli other, 

 and each rod moved 6 feet ; so that the men changed their position at each step. 

 By the advice of Mr. Loam, it was decided to substitute a steam-engine for the hy- 

 draulic wheel, so that the motive power could not fail, and at the same time it was 

 judged advisable to increase the stroke of the rods 12 feet; the number of the steps 

 and the distance between them remaining the same, so that the men had only to 

 change at every other one, and the same number of miners could ascend and descend 

 at once. 



On October 25, 1842, the machine, thus modified, had attained to the depth of 140 



