Management of Light in Illumination. 125 



One of the six chains by which the pendulous illu- 

 minators are suspended must be attached to its corre- 

 sponding arrow by means of a hook, in order that it 

 may be unhooked below, and laid aside occasionally 

 in order to open a passage between the two neigh- 

 bouring chains for removing the reservoir or the upper 

 hemispherical screen. 



As six chains are employed in suspending the brass 

 hoop on which the reservoir reposes, this hoop re- 

 mains suspended, even when one of these chains is 

 unhooked and laid aside ; and as these chains are not 

 attached immediately to the hoop, but at some dis- 

 tance (3I inches) from it, to arrows which project hori- 

 zontally from the outside of it, the opening between 

 the two neighbouring chains which remain after the 

 movable chain has been unhooked and laid back on 

 one of them is so wide that the reservoir or the hemi- 

 spherical screen can pass between them, without touch- 

 ing either of them. 



As these pendulous illuminators will burn well eight 

 or nine hours without being replenished, it will seldom 

 be necessary to refresh them with oil while they are in 

 actual use. If, however, that should be necessary, it 

 may easily be done, even without extinguishing them 

 and without danger. But, in general, the reservoir is 

 always to be taken away and carried out of the room 

 when it is to be filled, and the burners cleaned and 

 trimmed. 



In removing the reservoir, the following precautions 

 are necessary : first, the burners having been extin- 

 guished, the illuminator must be lowered down to that 

 height which is most convenient for lifting the reser- 

 voir out of its place ; or, in case the height of the room 



