198 Management of Light in Illumination. 



no more light than that which could be produced in 

 the combustion of 148 parts of wax. 



Hence we may conclude that the maximum of effect 

 with this lamp was obtained when it was made to fur- 

 nish 900 of light. 



The best effect produced with the lamp No. i was 

 when it gave 300 of light. 



And the maximum of the effect of the lamp No. 2 

 was that which was produced when it was so managed 

 as to furnish 500 of light. 



By comparing the quantities of oil which these 

 lamps consumed in furnishing these quantities of light 

 with the quantities of wax necessary for producing the 

 same quantities of light by means of wax candles, we 

 can ascertain how much cheaper any given quantity of 

 light can be produced by one of these lamps than by 

 the others, when they are all so managed as to produce 

 their best effect. 



300 of light were furnished by the lamp No. i with 

 an expense of oil which amounted to 201 parts per hour. 



To produce the same quantity of light, 300 parts of 

 wax must have been burned. Consequently, if 201 parts 

 of oil are equal in effect to 300 parts of wax, 100 parts of 

 oil so employed must be equal in effect to 149 parts 

 of wax. 



Again, it was found that 500 of light were furnished 

 by the lamp No. 2 with a regular consumption of oil, 

 which amounted to 357 parts. 



To have produced that quantity of light by means of 

 wax candles, 500 parts of wax must have been con- 

 sumed. Here 357 parts of oil were equal in effect to 

 500 parts of wax, consequently 100 parts of oil so 

 employed were equal in effect to 140 parts of wax. 



