MR. RONALDS ON PHOTOGRAPHIC SELF-REGISTERING INSTRUMENTS. 115 
Explanation of the Plates. 
PLATE X. 
Fig. 1. Electrograph. 
A. The body of the lucernal microscope ; its nearest side removed. 
B. The voltaic electrometer ; the pendulums b x suspended by hooks from 
an insulated piece b 2 . 
C. A board fitted to the end of A, and having a curved diaphragm (c 1 ) cut 
through it. The condensing lens is placed beyond this diaphragm (and 
not visible). 
D. The Argand fountain lamp, or a camphine lamp. 
E. The screen, with its slit (e 1 ). 
F. The case which receives the sliding-frame. f b . Springs pressing the 
glass of the frame (H. fig. 2) against E when the door is closed. 
G. The tube containing the achromatic lenses. 
Fig. 2. 
H. The sliding frame suspended in F. h l , h 1 , &c. Bolts and nuts for 
pressing the photographic paper between the two plates of glass. 
h 2 ,h 2 . Friction-rollers, f 3 . Spring for pressing H againsty 2 , the ruler. 
h 3 . Hooks. 
I. The pulley on the hour-arbor of the clock. i l . The line (of gut) sus- 
pending IT ; i 5 . the counterpoise (to H) suspended by i 3 ; i 2 , and * 4 , 
terminations of i 1 and i 3 . 
K. The time-piece. 
L. The transfer-box. 
Fig. 3. Thermometro graph. 
A. Section of the lucernal microscope. 
B. Thermometer; ft 1 , its tube; b 2 , its bulb. b 3 . Diaphragm fixed upon b ] . 
Fig. 4. Barometrograph. 
A. Section of the microscope. 
B. Siphon barometer. b l . Black pith-ball resting on the mercury. 
Fig. 5. Contracting Diaphragm. 
M. Plate having a slit cut through its central part. 
N. Small parallel ruler (of the common kind), w 1 and n 2 . Screws which 
pass through the centres of its cross-bars (with friction) and screw 
firmly into M in the line of the centre of the slit. 
Fig. 6. Distinguishing Electrograph. 
A. Section of the microscope. 
B. The voltaic electrometer. b x . The pendulums suspended from the piece 
b 2 . b 5 . A little plate attached to the lower end of b 2 between the pen- 
dulums. b b . A longer pendulum suspended by a hook from b b , and 
Q 2 
