122 Management of Light in Illumination. 



effectually prevent the oil from being spilled in trans- 

 porting the illuminator from place to place. It would 

 even be very difficult to make it run out at the open- 

 ings of the burners, for the pressure of the external air 

 would prevent it. 



As the reservoirs of the table illuminators are small, 

 two openings above, opposite to each other, have been 

 found to be sufficient ; but, when the reservoir is much 

 larger, three openings are useful, as they afford the 

 means of seeing when the reservoir is placed horizon- 

 tally, as also when it is completely filled with oil. 

 There never can be any use in opening more than one 

 of the passages for the admittance of air into the reser- 

 voir when the illuminator is lighted, and that is to be 

 opened which happens to be nearest at hand. 



A very important advantage has been obtained by 

 making the reservoirs of those illuminators large and 

 shallow; for, as the level of the oil in the reservoir 

 varies so little, the burners are always well supplied, 

 without employing any of those complicated contri- 

 vances which have been used for preserving the level 

 of the oil in Argand's lamp. As all these methods are 

 connected more or less with the elastic force exerted 

 by the air, and as that force varies with heat and cold, 

 these contrivances are liable to many inconveniences, 

 not to mention the awkward and complicated forms 

 they give to lamps, and the disagreeable nature of the 

 operation of filling their reservoirs with oil. 



If a lamp with an inverted reservoir, after having 

 burned some time, be extinguished and suffered to 

 cool, it must be filled anew before it can be lighted 

 again : otherwise the air which has found its way into 

 the upper part of the inverted reservoir, on being 



