1^44.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



S61 



by tliis process, completely cxomplifipd. To proceed a little further; 

 it is evident, that the angle and situation of the two looking-glasses 

 could be so arranged as to direct the rays of the sun through any par- 

 ticular pane of the windovv ; so that a person standing wilhoat, in a 

 proper position, would see, in .iddition to the sun's rays reflected from 

 the outer surface of the pane, the rays of incidence that had passed 

 through the window, ;ind were thus reflected from the double mirror. 

 One of the luminous olijects (the flush or glare of the sun) so produced, 

 would be reflected from the surface of the window, and would be a 

 single reflection; while the rays of incidence, which had p.issed 

 through the window, iind undergone a double reflection by means of the 

 two mirrors would, on being thrown back by the mirrors through the 

 window, move in a direction contrary to that taken by the !,ingle re- 

 flection from the surface of the window pane. Hence, any one of the 

 heavenly bodies, subjected to the eye by a process of the ;ibove de- 

 scription, would not onlv appear as two distinct objects, but those ob- 

 jects would be seen to approximate and cross each other in i\n opposite 

 course : a desideratum being hereby secured which increases the 

 power of the instrument in a double ratio, and renders it prnportion- 

 ably preferable to any other that h;is been hitherto employed. 



The wood-cut, fig. 3, represents a Dipleidoscope fitted up with a 

 telescope, and having all the usual meridian and vertical adjustments, 

 to be efl'ected by means of the screws, a, b, c. This form of mounting 

 the instrument is suited to the observatory or library, where it should 

 be placed on a pedestal of stone or cast-iron. 



Fig. a. 



The wood-cut, fig. 1, at the head of this article, shows the instru- 

 ment fixed on a pedestal in the open air ; for as the workmanship is 

 impervious to the weather, it needs no further protection than the 

 brass covering with which it is supplied. 



THE SEWERAGE OF DERBY. 

 Fig. l.-Section of New Sewer. Th£ new sewerage of Derby 



extending from the Morledge to 

 Cheapside, designed by Captain 

 Vetch, R.E., has been let by the 

 Commissioners of the Derby im- 

 provement Act, for the sum of 

 3,200/. to Messrs. Booth and 

 Thompson, of Rotherham. The 

 principal work is a sewer 10 feet 

 diameter and 9 feet in height, and 

 about 709 yards in length. The 

 section is nearly a square, see fig. 

 1, with a segment of a circle 

 added on all sides, being arched 

 at top, and the dish of the invert 

 at bottom, and the batter of the 

 curvilinear side walls, making the 

 appearance above described. The 

 arch and side walls arr from 

 1 to li brick in thickness, as circumstances require, the invert being 

 only 1 brick throughout. The course of the sewer is as follows: — 

 commencing at the junction of Cheapside with Wardurck along the 

 latter place, and Victoria Street and St. Peters Street, and down 

 ThorutoD Lane and the Morledge to Cockpit Hill. By reference to 



the plan of Derby, this course will be very clear, and the cause of this 

 expenditure will be in the recollection of your readers to have arisen 

 from a sudden inundation of the town about three years ago, when the 

 market-place was flooded in a sudden manner, supposed to have arisen 

 from a water spout bursting above the town, on the course of the 

 Derwent. 



Fig. 2.— bection tluough A D, of bg. 3. 



The situation of the town is very low and is intrrsected with rivers, 

 brooks, and canals, and the engineers have had recourse to the passing 

 of Becket Well Brook, underneath the sewer, by a cast iron syphon. 

 The water in the brook being retained to a certain level, the surplus 

 running over a waste weir into the new sewerage, and the body of 



water in the brook being passed underneath the sewer, and continuing 

 its course. This ingenious plan of the engineer is shown in the an- 

 nexed engravings. Fig. 1 is the section of the main sewer; fig. 2 is 

 a section of the sewer, showing the passage of the brook or syphon 

 under it ; and fig. 3 a transverse view of the brook syphon; tig. 4 is a 

 section of the gully holes or grate drains, with trap ; fig. 5 transverse 



Fig. 4.— Section of Gully Hole. 



section of drain at C D. Fig. I also shows the difliculty occuring in 

 Thornton Lane, also a comparative view of the size of the old (a) and 

 new sewers. In calling attention again to drawings 2 and 3, of Becket 

 Well Brook, it is obvious the drainage might be ail the depth cf the 

 water pent up in the brook improved, if it were not for the purpose 

 of preserving right in the stream. 



O. T. 

 Nemcastle-o)fTyne, April 18, 1844. 



