16/52 In Herschel's Telescope the great mirror is inclined so that the image is formed at a slight distance from the axis of the telescope. In the two first cases the object is viewed in the usual or direct way, the image being erect in Gregory's and inverted in Cassegrain's. In the third the observer looks through the side of the telescope, seeing an inverted image of the object. In the last the observer sees the object inverted, but not altered as respects right and left. The last-mentioned method of viewing objects is the only one in which the observer's back is turned towards the object, yet this method is called the _front view_--apparently _quasi lucus a non lucendo_. |