498 INVESTIGATIONS RELATIVE TO ILLUMINATING MATERIALS. 



ing at the open end in a small cup, from which the burner is directly 

 supplied with oil on the well-known principle of the bird fountain, this 

 vessel being filled with oil by inverting it and pouring in the liquid 

 through the open end of the tube. It is then reinverted and the end of 

 the tube inserted in the small cup below the level of the oil which it 

 contains. The oil in the reservoir in this condition is supported by the 

 pressure of the atmosphere on the surface of the oil in the cup. When 

 this surface is lowered by burning, the end of the tube is opened, and 

 a bubble of air passes up and an equal bulk of oil descends, and in this 

 way a nearly constant level of oil is maintained. I say nearly constant 

 because the air which goes up is of some volume and in the act of pass- 

 ing up produces an oscillation which, in some degree, affects the stead- 

 iness of the burning of the flame. 



There is however a greater defect in this lamp from the oscillations in 

 the level when the reservoir has been exhausted of a considerable por- 

 tion of its charge of oil. In this case the arrangement is one similar to 

 an air thermometer with a large bulb, and is affected by a sudden draught 

 produced by the opening and shutting of a door or the ordinary ventila- 

 tion of the lantern. This Avas partly remedied by bending the tube, and 

 thereby increasing the resistance to a sudden change in the level of the 

 oil. 



The improvement of .Mr. Funck consisted in substituting for these 

 lamps one of constant level, in which the oil is placed above the burner, 

 and the flow of oil necessary for perfect combustion is regulated by a 

 small floating piston, placed in an enlarged portion of the supply -tube, 

 and carrying on its ujjper surface a conical projection which increases 

 or diminishes the size of the supplying orifice in accordance with the 

 rajjidity of combustion. This lamp is not only free from the objections 

 pertaining to the other lamps, but is less expensive and better adapted 

 to the burning of lard-oil. It affords a freer combustion, and conse- 

 quently a more intense light, though at the cost of a larger amount of 

 the burning material. 



In this lamp the heated air and products of combustion i)ass through 

 a cylindrical opening in the reservoir, which is placed directly above 

 the lamj), the opening in it forming as it were a prolongation of the 

 chimney, thus not onl}' i)reventing the oil from freezing in the coldest 

 weather, but supplying it to the burner at the temperature best adapted 

 for perfect combustion. 



In regard to the comparative character of lard and colza oil, we may 

 be allowed to print the following letter from Colonel Hamilton, the man- 

 ufacturer of the latter oil, who was present at the trial to which he 



alludes : 



Fond du Lac, Wis., May 16, 1868. 



Dear Coivoiodore : I must confess my great disappointment at 



the result of the experiments at Staten Island. It is however not reaUy 



so much the failure of rape-seed oil, as the undeniable excellence of lard- 



