APPLIED MECHANICS. [FLCID COMMUNICATION or POWE. 



great prime-mover, luch a* a steam-engine or water- 

 wheel, U communicated by shaft*, pulley*, straps, and 

 wheel-work, to the dihVn-nt machines. However ex- 

 cellent may be the arrangement* or workmanship of the 

 connecting machinery, still there must bo considerable 

 waste of power in overcoming the mere friction attend- 

 ing its motion ; and this waste U very much increased 

 when the accuracy of arrangement is alfectod by wear, or 

 by the unequal settlement of any part of the building 

 supporting the bearings of shafting. Of late years, 

 engineer* nave devoted attention to the communication 

 of power, to some extent, without the intervention of 

 wheel-work and shafting, but by the supply of steam 

 from a central boiler to numerous small engines, arranged 

 throughout the building, in the immediate neighbourhood 

 of the machinery to be put in motion. The pipes that 

 convey the steam are cheaper in first cost than shafting 

 of < i juiv.ili-nt length ; their efficacy is not dependent on 

 accuracy of levels, nor is it impaired by wear ; ami ; 'if 

 friction attending the passage of steam through them is 

 much less than the friction of shafting. It is true that 

 the force of steam passing through great lengths of pipes 

 U considerably diminished by cooling ; but much of this 

 loss may be saved by covering the pipes with non-con- 

 ducting materials, such as felt or sawdust, and by super- 

 heating the steam in the first instance. The objection 

 generally made to this mode of communicating power is, 

 that the first cost of the numerous small engines generally 

 exceeds that of one large engine, and that each of the 

 small engines requires separate attendance. We believe, 

 however, that, iii an extensive work, the cost of steam - 

 pipes and numerous small engines will not be found to 

 exceed that of a large engine, with all the shafting and 

 connecting machinery ; and that, with proper arrange 

 mvnts, the attendance given by workmen to the separate 

 machines will be sufficient for the engines that put them 

 in motion. A number of machines are now made to act 

 directly by steam-power, without the intervention of 

 machinery. Among them we may cite, as examples, the 

 team-hammer and steam riveting machine. In both 

 these cases, the direct pressure of steam upon a piston 

 takes the place of the former complicated arrangements 

 of wheel-work, eccentrics, cams, and levers, which were 

 necessary for converting the rotary motion of shafting 

 into the reciprocating movements required -for hammer- 

 ing and riveting. To many other manufacturing opera- 

 tions we think the same principle of movement might be 

 with good effect ; and we believe that the sim- 



plicity, directness of action, and facility of control at- 

 tending such arrangements, would soon cause them to 

 take the place of the more complicated methods of 

 deriving power from rotary motions.* 



The atmospheric railway is an example of an arrange- 

 ment for communicating power on a large scale by means 

 of the fluid motion. A pipe, several miles in length, 

 with a longitudinal slit or opening along its upper side, 

 U laid down between the rails. The pipe is fitted with 

 a piston, and the slit is covered by a flexible valve, 

 which can be lifted so as to permit an upright rod at- 



tached to the piston to pass through the upper part of 

 the pipe to a carriage mounted on the rails. When the 

 carnage and piston are at one end of the pipe, the 

 valve being closed tightly over the slit, and luted by 

 grease melted over it, the air is extracted from the pipe 

 by pumps worked by a steam-engine ; and the pressure 

 of air on one side of the piston being thus in a great 

 measured removed, the atmospheric pressure, acting on 

 the other side, forces it along the pipe with great velocity. 

 ami thus gives motion to the carriage which is connected 

 with the piston and the train of carriages attached to it. 

 The piston and connecting-rod are fitted with suitable 

 rollers for lifting the valve in front of the upright rod, 

 and for closing it and sealing it up behind it ; so that 

 after the passage of the train in one direction, the pipe 

 may be ready for exhaustion to draw a train in the op- 

 posite direction. In the trials made with this system of 

 propelling trains, it was found possible to secure great 

 velocities, and to move very heavy trains over severe in- 

 clinations when the pipe and its valve were in good order. 

 But the great practical difficulties attending the construc- 

 tion and tight-closing of the valve proved an almost in- 

 superable objection to the use of the atmospheric railway, 

 as even a small leakage of air into the vacuum-pipe 

 necessitated the expenditure of great power in the pump- 

 ing engine to sustain the required vacuum. 



It was at one time proposed, that in the case of a city 

 like London, with numerous small steam-engines and 

 boilers scattered through it, power should be communi- 

 cated to different establishments from some central 

 source, by means of compressed air forced through pipes 

 laid down like the gas and water-pipes in the streets. 

 One large engine, continually sustaining a supply of air 

 condensed to a pressure of several atmospheres, would 

 thus take the place of the numerous separate boilers now 

 supplying steam, and the air thus supplied would work 

 the present engines as effectually as the steam. There 

 is little doubt that, were such an arrangement carried 

 out, the first cost of the air-pipes being met, there would 

 be considerable advantages attending it, in respect of 

 economy and the diminution of danger from boiler ex- 

 plosions, as well as the removal of numerous sources of 

 offence from the chimneys of manufacturing establish- 



lIlL'M-i. 



Arrangements of a similar character might at present 

 I>e carried out in cities like London without any great 

 outlay, where the supply of water is adequate. The 

 Dumping engines of the water companies might be made 

 ;ho means of supplying power to numerous establish- 

 ments of machinery at a very cheap rate. It is found, 

 practically, that in pumping water, 1 ton of fuel is capable 

 >f raising 25,000 gallons of water 100 feet high ; and as 

 water from a cistern 100 feet high would press with a 

 force of 46 Ibs. on every square inch of a piston exposed 

 to its action, this power might be readily made available 

 for raising weights, giving pressure, or even driving 

 machinery by the intervention of properly constructed 

 water-pressure engines, t 



CHAPTER VIII. 



RULES AND TABLES. 

 ConttnU. SYMBOLS OF ARITHMETICAL OPERATIONS WEIGHTS AND MEASURES TEMPERATURE ARCS AND ANGLES 



CIRCUMFERENCES SUPERFICIES SOLIDS SOLIDS OF REVOLUTION DUODECIMALS WEIGHTS OP MATERIALS. 



methods of calculation, which most commonly occur in 

 practice. 



[Many of these rules have been dealt with already in 

 a scientific form in the section on Mathematics, but this 

 statement, in a simple and concise form, may render 

 them more easily understood by persons not familiar 

 with abstract scienjej. 



t Since the completion of the Loch Katrine water-world, br meant of 

 which Glasgow it auppiied with water at a high prcwure, many imall 

 water engine! hare been erected for working enact, &c., which an 

 charged at a fixed annual rental. tu. 



Tur. practical mechanic has frequent occasion to calculate 

 the lengths of lines, areas of figures, capacities of solids, 

 Mid weight* of manse* of material. We think, therefore, 

 that we cannot butter conclude the general view we have 

 endeavoured to give of mechanic* practically applied, 

 than by furniihuig a few of those simple rules and 



In Maaebttr and Olaacnw It b nraal to Hz separate ateara- engine 

 to rath caUen-prlmnf mbine. partly for the reaaoni awlgned above, 

 aw! alae Uut each aa>ln mar b* tndrpendem of a main moving power, 

 -~ MI Ut readily ratted to anil tha ciigcncio of the 



