3/6 SECTION MECHANICS. 



arrangements for periodical trials, have stimulated engineers to devote 

 their best energies to the subject. No. 1942 is a model of one of 

 Aveling and Porter's common road traction engines, capable also of 

 acting as a source of power for driving farmyard machinery, or for 

 effecting steam ploughing. Upon the wall I have placed rough dia- 

 grams of another kind of traction engine a kind wherein india- 

 rubber tires are used. This is manufactured by Messrs. Ransome, 

 Sims, and Head ; and I have also placed diagrams of the ordinary 

 Portable engine and of another most useful kind of Portable engine 

 the Steam Fire engine. I have there likewise a sketch of Hancock's 

 common road steam coach, which some thirty years ago regularly plied 

 for hire from the Bank to Paddington in opposition to the ordinary 

 horse omnibus. Hancock's carriage was a vehicle which in my 

 judgment has never since been surpassed, and I ajn sorry to say 

 never to my knowledge equalled, as regards the various points which 

 should be attended to in making a steam carriage to circulate safely 

 among horse traffic. 



There is another way in which steam may be employed as a 

 prime-mover. We saw that water in the form of the trombe-d'eau 

 could induce a current in air, and thereby blow a forge fire, and that 

 a rapid stream could be caused to induce a current in other water, 

 and thus drain marshy lands. Similarly steam can be caused to 

 induce a current in water, and thereby impel the water so as to raise it 

 to a height, or to force it as feed water into a boiler against a heavy 

 pressure. When used for a mere pumping apparatus such a mode of em- 

 ploying steam is very wasteful, because the steam is condensed in large 

 quantities by the water, and the water is needlessly heated at the 

 expense of the steam ; but when used in feeding a boiler the whole of 

 the heat is taken into that boiler, and thus this objection does not 

 apply. By means of that most elegant and scientific apparatus, the 

 Giffard injector, it is possible by a jet of steam to induce a current in 

 surrounding water powerful enough to take the water and the con- 

 densed steam into the boiler from which the steam had previously 

 issued. No. 1976, which I have before me, is a sectional model of a 

 Giffard injector. 



I believe it was I who first gave a popular explanation of the 

 principle of action of the Giffard injector; and although a Scien- 



