TRANSACTIONS OF SECTION G. 



881 



The present paper describes a more recent invention of tlie author's by means 

 of which a far greater degree of expansion is made possible. 



When an engine has heavy reciprocating parts, such as long pump rods or 

 loaded plungers, expansive working is possible because of the inertia at the 

 beginning and the momentum towards the end of the stroke, expressed by the 



wv- 



formula -^ By this method for a considerable degree of expansion a very 



high velocity must be given to the mass when the weight is small. In engines 

 which have not long pump-rods it is not always convenient to provide weights 

 sufficiently heavy to enable a high degree of expansion to be employed. The 

 mechanism which the author proceeds to describe practically equates the engine 

 power and the pump resistance by causing the decreasing pressures of the expanding 

 steam on the piston of the engine to bring a nearly constant force to bear on the 

 pump throughout the stroke. 



In figure 1 let the pump resistance be represented by the parallelogram a, b,c, d, 

 and the engine power diagram by the figure c, e, f, 

 y, d, and supposing the parts of the engine to have 

 no weight, then means are required by which the 

 piston of the engine may move with A'arying velo- 

 cities relative to that of the pump piston, exceeding 

 the mean velocity by the ordinates 1,2, 3, and fall- 

 ing short of that velocity by the ordinates 4, 5, 6. 



Let A (figure 2) be the engine, and B the pump 

 piston, and C a triangular frame turning on the ful- 

 crum D. The pump piston is attached to the frame 

 at the point E by means of a vibrating connecting 

 rod, and the engine piston to the point F by means 

 of a similar rod. Whilst the engine is making its 

 stroke in the direction of the arrow the pump piston 

 is decreasing in velocity relative to that of the en- 

 gine piston, the ratio being determined by the rela- 

 tive positions of E and F. 



In applying this mechanism to pumping engines 

 it is first necessary to determine the ratio of ex- 

 pansion to be employed, and then to see how nearly 

 the force and resistance can be equated. 



Let a, h, c, d, e (fig. 3) be the combined 

 diagrams of a compound engine working with 

 the given ratio of expansion, a, f, g, e, the diagram of effects of the varying 

 velocities of the engine and pump pistons, and a, h, i, e, the piunp-resistance dia- 

 gram. Then acceleration of velocity takes place from h, c, and knowing the 

 weight of the moving parts the acceleration may be calculated. It \vill at once be 

 seen that the mechanical advantage obtained by this mechanism greatly reduces 

 the acceleration for a given mass. 



5 



4. Reinforcing Electrical Contacts so as to increase their Reliability, with 

 Example of Ajjplication to Reeling Silk from the Cocoon. By E. W. 

 Sekbell, Jun, 



The object of the paper is to explain a method of securing a good electric con- 

 tact under circumstances in which ordinary solid or mercury contacts will not work. 



The method consists in the use of a sucking coil or small electro-magnet, placed 

 near the contact and traversed by the whole or a part of the current when the 

 circuit is closed. When the contacts touch, no matter how lightly or imperfectly, 

 the magnet or coil is excited, and acts on an armature in such manner as to cause 

 the parts of the contact to be drawn more firmly together and to scrape over one 

 another so as to be cleaned by a mechanical action produced by the current itself 

 every time that contact is made. By this method all the difficidties commonly 



1887. 3 L 



