We may carry out this a little further by imagining a varied treatment on plan of a marked-out space of a certain size and proportion, on which a church of some kind, for instance, is to be placed. The simplest idea is to inclose it round with four walls as a parallelogram (Fig. 30), only thickening the walls where the weight of the roof principals comes. But this is a plan without an idea in it. The central or sacred space at the end is not expressed in the plan, but is merely a railed-off portion of the floor. The entrance is utterly without effect as well as without shelter. If we lay out our plan as in Fig. 31, we see that there is now an idea in it. The two towers, as they must evidently be, form an advanced guard of the plan, the recessed central part connecting them gives an effective entrance to the interior; the arrangement in three aisles gives length, the apse at the end incloses and expresses the _sacrarium_, which is the climax and object of the plan. The shape of the ground, however, is not favorable to the employment of a long or avenue type of plan, it is too short and square; let us rather try a plan of the open area order, such as Fig 32. This is based on the short-armed Greek cross, with an open center area; again there is an "advanced guard" in the shape of an entrance block with a porch; and the three apses at the end give architectural emphasis to the _sacrarium_. Fig. 35 is another idea, the special object of which is to give an effect of contrast between the entrance, approached first through a colonnaded portico, then through an internal vestibule, lighted from above, and flanked by rows of small coupled columns; then through these colonnaded entrances, the inner one kept purposely rather dark, we come into an interior expanding in every direction; an effect of strong contrast and climax. If our plot of ground again be so situated that one angle of it is opposite the vista of two or more large streets, there and nowhere else will be the salient angle, so to speak, of the plan, and we can place there a circular porch--which may, it is evident, rise into a tower--and enter the interior at the angle instead of in the center; not an effective manner of entering as a rule, but quite legitimate when there is an obvious motive for it in the nature and position of the site. A new feature is here introduced in the circular colonnade dividing the interior into a central area and an aisle. Each of these plans might be susceptible of many different styles of architectural treatment; but quite independently of that, it will be recognized that each of them represents in itself a distinct idea or invention, a form of artistic arrangement of spaces, which is what "plan," in an architectural sense, really means. * * * * * THE LOWE INCANDESCENT GAS BURNER.