14 



power objective furnishes a first-class achromatic condenser for 

 the high power. It is surprising what good results may be ob- 

 tained with this simple apparatus. 



The other features of the outfit are sufficientlv displayed in 

 the illustrations. The' rotating tables are of the usual type, 

 though above the usual size. They carry five by eight swing 

 drawers and hanging shelves for books and instruments. 



THE DARK ROOM. 



A peculiarity of the Division dark room that deserves men- 

 tion is its illumination. This is carried out on a plan that has 

 often been adopted for small dark-room lamps, but has not 

 hitherto, so far as the writer knows, been carried out on a large 

 scale adapted to daylight as well as artificial light. 



The non-actinic or "safe" light for the dark room is obtained 

 by passing daylight through suitable solutions, and the illumina- 

 tion is from above after the manner of numerous patterns of 

 small dark-room lamps. The dark room window is placed some- 

 what higher than is usual and its upper sash is boxed in in a 

 light-tight manner. The! box is prismatic in form: one side is 

 parallel to the side of the dark room, in fact coincides with it; 

 another is perpendicular to the side of the dark room' and forms 

 the horizontal bottom of the box, while a third is at an angle 

 of 45°, such that when a mirrow is fastened on its inner surface 

 it reflects the sky light, which comes through the window and 

 throws it downward upon the dark room sink and developing 

 board. On the bottom of this prismatic box, there rests a tray, 

 or a number of trays nested one over another, for the reception 

 of the various colored fluids used as light screens. One of the 

 most useful of these fluids is a concentrated solution of bichro- 

 mate of potash. 'It is found that ordinary daylight or sunlight 

 on bemg passed through from eight to twelve inches of con- 

 centrated solution of bichromate of potash is a very sufficient and 

 satisfactory light in the dark room, especially when it is reflected 

 from above m the manner described.* The mirror used for re- 

 flectmg the light downwards is preferably of corrugated glass 

 though plam glass answers the purpose. The box contains an 

 electric or gas light so that it is available for evening work The 

 amount of comfort to be gained from an ample illumination in 

 the dark room is something that should not be overlooked as 

 the frequent passage from the dark room to an illuminated room 

 IS a trymg matter,_ even for the best of eye-sight. The amount 

 of dlummation which may be secured by adoptin^r the plan here 

 described may be readily judged when it is said that during de- 



direcnfinKM7he"uMnrtmV'tl,°„r''l^.'' ^"^'^ aymri,™ full of the solution r>laced 

 downward as described ""' ^^^ ""■'''"^ through it being afterwards reflerted 



