498 SUMMARY OP CURRENT RKSEAKGHEP. 



illumination on the drawing board when the carnera-lucida is in use (see 

 fig. 60, 32, 36). 



We will next pass to a descriotion of the Microscope window. This 

 faces the sun, and preferably faces precisely south. It is so fitted with 

 light-proof roller blinds that the light may be entirely shut off, or may 

 be allowed full access. The roller blinds slide in lateral grooves 10 in. 

 deep. The depth of these grooves must be sufficient to prevent the 

 blinds bellying through the action of the wind. It is found when a 

 window is tightly closed with flexible blinds, as is the case in this special 

 Microscope window, that the pressure of the wind is sufficient to cause 

 considerable inconvenience, unless the edges of these roller blinds are 

 held in deep grooves. Should it be necessary to make a further pro- 

 vision against the bellying of the blinds, they may be stiffened from 

 place to place with y 1 ^ in. wooden laths ; or wires may be strung across 

 the window. The blinds may be of any opaque material, but if they 



Explanation of Fig. 60. 



1, 1, 1, Pulleys for the sash cords 2 ; 2, 2, steel sash cords for the slides 12 

 and 21 ; 3, 3, two vertical steel girders passing through the floor without contact, 

 imbedded in several tons of cement under the building ; 4, 4, steel sash cords, 

 same as 2 ; 5, wooden frame-work to stiffen the girders 3, 3 ; 6, 6, the two upper 

 opaque sashes to the side windows of the bay ; 7, 7, sash weights counterbalancing 

 the cross-arms 12 and 21 ; 8, one of the two similar light-proof roller blinds ; 9, 9, 

 Anti-friction bearing for the arms bolted to the cross-piece 12 ; 10, anti-friction 

 bearings for the arms of the cross-piece 21 ; 11, lower opaque wooden sash of the 

 left hand window ; 12, cross-piece for the attachment of the camera 18 and the 

 camera lucida prism 24 ; 13, screw clamp to cross-piece 12 ; 14, lower opaque 

 wooden sash to right hand bay window ; 15, slot in which the camera lucida arm 17 

 slides horizontally ; 16, clamp to the cross-arm 21 ; 17, arm for the support of the 

 camera lucida prism 24 : 18, ordinary camera attached to arm 12 ; 19, Microscope 

 camera attached to arm 21 ; 20, vertically sliding head-rest ; 21, wooden cross-arm 

 supporting Microscope camera 19, and head-rest 20, and drop slide 32 ; 22, battery 

 of Microscope, using direct sky- light ; 23, screw clamp to cross-arm 21 ; 24, large 

 45° camera lucida prism ; 25, location of the camera lucida drawing, vertically 

 adjustable by means of steel cord and sash weights similar to 7 ; 26, pillow to head- 

 rest ; 27, wide thin metal curtain stick to the inside roller blind 8 ; 28, ways for 

 the horizontal thin metal slide 29 ; 29, thin metal slide with diamond shaped 

 opening 31 ; 30, small camera lucida prism of the usual pattern ; 31, diamond- 

 shaped opening in the slide 29 ; 32, thin opaque drop slide adjustable vertically 

 through foot power, by means of simple pulleys located behind 17 and the foot 

 power 40, 41, and 42 ; 33, left-hand adjustable leg-of-mutton shaped table ; 34, 

 right-hand adjustable leg-of-mutton shaped table ; 35, opaque dark cloth enclos- 

 ing sub-stage of Microscope, preventing access of extraneous light ; 36, aperture 

 for the admission of light, glazed with ground glass, and opened and closed by 

 means of slide 32 and foot power 40, 41, and 42 ; 37, steel sleeve carrying Micro- 

 scope, and vertically adjustable on the pillow 38 ; 38, steel pillar for support of 

 Microscope, passing through floor without contact, and imbedded in several tons 

 of cement under the building ; 39, aperture in floor for the passage of girder 38 ; 

 40, spring-roller foot power for the control of drop slide 32 by means of the string 

 passing around the pulley 42 ; 41, spring roller of ordinary pattern, covered with 

 sand-paper to give sole of foot efficient grip ; 42, pulley turned by foot power, and 

 winding or unwinding the string which raises or lowers the drop slide 32 — the 

 weight of drop slide 32 exactly counteracts the spring of the roller 41 ; 43, left- 

 hand steel girder at height of floor ; 44, steel sleeve sliding vertically on left-hand 

 girder and affording attachment for table 33 ; 45, steel sleeve sliding vertically on 

 right-hand girder and affording attachment for table 34. 



