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244 DETAILS OP SCEEW ENGINES.

CHAPTER VI.

DETAILS OP ENGINES POE SCEEW PEOPULSION.

The “ screw engine,” as it is usually termed,has many advocates of various opinions, inas-much that rarely, even with the details,do two makers agree as to the design. Ofcourse, as to the principle, there can be butone aim in view; the difference,' therefore,pertains to the mechanical question. Thismuch, however, must he acknowledged, thatif by adverse opinions, many modes—eachproducing the same result—are originated,no little credit is due to those engagedthereon. When cogitating on a new idea fora given purpose, the mind should not beswayed in one direction; rather should thedefects be remembered than set aside, bywhich means a truthful conclusion must bearrived at. Two facts should be ever beforethe designer —“ simplicity of construction,”and u access for repair. ” Now it may be urgedthat the latter consideration is an admission ofa defect, to be retained, rather than obviated.It can be said in answer, however, thatnatural laws have not, to the present, beenfathomed deeply enough to ignore repair, andthat more wisdom is displayed by the generalwho deliberately prepares for the reception ofthe enemy, than he who relies on suddenaction. Of course, confidence in the matterin hand must not be omitted, for without self-credit no inventor or schemer can proceed. A

sure means of success is to acknowledge thefaults committed, and obviate them in the nextexample, rather than be led by conceit in theaccomplishment of one object.

In pages 38 to 75, the variations in thearrangements of the screw engines have hadattention : the present chapter is in connectionwith the same, in direct allusion to the detailsof the previous examples.

The condenser of a horizontal enginedetermines the lateral disposition of the cylin-ders, obviously so, on remembering that whenthe pumps are worked by the steam piston,the centres of the former must be within thecircle of the cylinder’s area. It is with a justrecognition of this fact that the condenserswill have prior notice in this chapter.

NJECTION CONDENSEES, WITH THUNKAIE PUMPS.

The type of condenser first to be noticedis fitted with the trunk air pump. Of thisclass, two firms only—one in England andthe other in Scotland —at present adopt thesame. The illustration, Fig. 73—page 245—is an elevation of the condensers of theengine illustrated by Fig. 4—page 44. Theplunger is a hollow tube, with a closed end,forming a separate portion, secured by boltsand nuts. The connecting-pin of the con-