REPORT OP THE POLYTECHNIC ASSOCIATION. 41 



lamp it is frequently of advantage to supply heated air, thus 

 increasing the volume and diminishing pro rata the injurious 

 excess ; but without a chimney, heated air rising around is less 

 adapted for concentrated combustion. 



But tliere is also waste combustion above the burner and heat- 

 abstracting apparatus, when the combustible vapor is driven 

 upwards with a force which prevents its immediately mixing with 

 air; it is then burnt on the outside in so thin a film as to be non- 

 luminous. This was tested in the course of this examination in 

 this way — a peculiarly steady flame was taken — a wire placed in 

 non-luminous flame (alcohol or a Bunsen's burner,) is ignited and 

 renders it luminous ; in the centre of the. dark part of the 

 kerosene flame it remained dark, indeed actual cooling was 

 observed, when a wire, previously ignited, was introduced into 

 it ; lamp black volatilized in the centre also, did not become 

 ignited, while if it was retained in the burning film on the out- 

 side it grew hot, and when withdrawn into the air it kindled. 

 These films, dark when looked at directly, were luminous when 

 seen obliquely. I submit that this shows total absence of com- 

 bustion in the centre, and absence of free oxygen in the bujrning 

 film on the outside ; also that a flame requires a certain thick- 

 ness to appear luminous. This combustion without light meas- 

 ures the waste of combustible with increase of blue flame, or 

 with equal areas it is inversely as the thickness at that part. • 



Mr. Smith has offered no results in opposition to the received 

 opinion that a flame owes its luminousness to incandescent car- 

 bon. Such experiments are necessary to establish the economy 

 of attempting to obtain light from burning alcohol as in No. 5. 



Comparisons of the relative cost of difl'erent sized flames yield- 

 ing variable quantities of light for uncertain periods, have given 

 no exact results. The lamps Nos. 1, 2, 4 and 6, were taken into 

 use as soon as received, and were repeatedly tested in various 

 ways. I am familiar with a burner similar to No. 3. It requires 

 a special lamp and wick — neither were furnished, and it has not 

 been specially tried. It is intended for less general use than the 

 former ones — it is partly based on the same principles, and the 

 class of burner is inferior to them in nearly all but cheapness. 

 No. 5 has been tried as far as suited the inventor. I have been 

 assisted by other members of the section, and the conclusions 

 obtained are confirmed by those who have used the lamps. 



The principle of mixing the vapor of coal oil (schist oil) with 



