\ 



Description of a Portable Diorama. 275 



geodetlcally, 'With precision, the latitudes and longitudes of all the im- 

 portant points throughout the British Isles. 



May all these important labours be speedily brought to a satisfactory 

 conclusion, for the benefit of both agriculture and commerce, since, in the 

 present state of our maps, the most palpable and dangerous errors, not- 

 withstanding all that has been urged for their correction, still continue 

 to exist, as will readily appear by an examination of the maps now sub- 

 mitted for inspection. 



*** A few maps and charts were here exhibited, containing glaring 

 and dangerous errors to navigators. 



Descripiioji of a Portable Diorama, which may be viewed by a 

 number of persons at a time. By George Tait, Esquire, 

 Advocate, F.R.S.S.A. With a Plan. Communicated by 

 the Royal Scottish Society of Arts.* 



A portable diorama which I exhibited to the Royal Scottish 

 Society of Arts in November 1841 and April 1812, and which 

 was honoured with their medal, could be viewed by only one 

 or two persons at a time, the pictures being within the box, 

 and being seen through eye-holes.t 



1 have now made a diorama having the construction modi- 

 fied so that it may be viewed by a number of persons at a time, 

 the pictures being placed upon the front of a box, where they 

 are exposed uncovered. The front light is thrown upon them 

 from without, and the back light from within, the box ; and 

 both may be increased or diminished at pleasure. Gas is 

 the most convenient light ; but oil may be employed, by adopt- 

 ing means for properly increasing or diminishing the light 

 upon the pictm-es. The apparatus is used in a dark apart- 

 ment ; and ought to be so placed that the horizon of the pic- 

 tures may be on a level with the eye. The effect of coloured 

 sketches of a variety of changes which I made for the former 

 diorama, is equally satisfactory in this. 



The following side-elevation and plan represent a small 

 diorama made upon this principle : — 



* Read before the Eoyal Scottish Society of Arts, on 23d January 1843. 

 t See the printed Transactions of the Royal Scottish Society of Arts, and 

 the Edinburgh New Philosophical Journal for 1841, 1842. 



