494 INVESTIGATIONS EELATIVE TO ILLUMINATING MATERIALS. 



introduction of lard-oil and in the preliminary experiments for deter- 

 mining its quality. 



A photometer room was afterward fitted up in the Smithsonian Insti- 

 tution, in which several series of investigations were made in regard to 

 the illuminating power of different oils. At the same time a series of 

 experiments was undertaken relative to their chemical characters and 

 conditions ; in which experiments the chairman was assisted by Prof. 

 C. M. Wetherill, whose untimely loss the science of this countr3^ has 

 been called to mourn. Among the investigations in the laboratory are 

 the following, relative to the expansions of different oils, intended to 

 facilitate the purchase, the measurements being made at different tern, 

 peratures. To obviate the necessity of the correction for temperature, 

 the oil is now purchased by weight. The following results may how- 

 ever be of value in the application of different oils to light-house pur- 

 poses: 



EXPERIMENTS UPON LIGHT-HOUSE OILS, 

 [Density and volume of oils (and water) at difterent temperatures.] 



