122 report— 1878. 



and the gas jets placed in position and accurately adjusted by the governor 

 to exactly two candles. Both meters were placed on the left side, and close 

 together, and were provided with three-way cocks, so that the gas could be 

 turned off or on each meter without disturbing the burning of the gas. 

 In making the test with the candles, these were carefully selected and 

 prepared, and after being lighted were allowed to burn for twenty minutes 

 before the test was proceeded with. The photometer room was large and 

 well ventilated, but absolutely free from sensible currents of air ; dia- 

 phragms covered with black velvet were placed in well-selected positions, 

 and all surfaces which by any possibility could reflect light were also 

 covered with the same material. After working for some hours the gas 

 was tested again in order to ascertain whether its quality remained con- 

 stant, and if it had changed sensibly the tests which had been made 

 were rejected. 



Experiments were made in order to ascertain the loss of light result- 

 ing from the use of globes of different kinds and of various shapes. The 

 loss is always considerable and in many cases excessive, and it results 

 partly from the absorption of light from the material of the globe and 

 partly from the draught caused by the ascension of the heated air in the 

 confined space. As regards material, a piece of clear window-glass held 

 in front of a gas flame diminishes the light to the extent of about 10 per 

 cent., but in the case of a clear globe it is in some cases less owing to 

 the reflection from the surface farthest from the photometer. Globes 

 frosted or ground all over, technically known as " moons," absorb about 

 25 per cent, of the light when well shaped, and opal or " cornelian " globes 

 40 to 50 per cent., according to the thickness and quality of the glass. 

 The following results were obtained with globes of different sizes ground 

 all over, and shew the effect of increased draught in diminishing: the 

 light:- 



A 6-inch globe caused a loss of 25 per cent. 



A 10 „ „ „ „ 38 „ 



All these globes had the usual sized opening below — about If inches in 

 diameter. Experiments were made with clear 1\ inch globes, having 

 openings below varying from 2f inches to 1 inch in diameter. The 

 source of light was a Bronner batwing, No. 5 top, No. 4 bottom, burning 

 under a pressure of 1 inch 3*35 cubic feet of gas. 



The naked flame gave a light of 16-8 caudles. 



With clear globe, opening below 2| inches, 154, loss 8-0 per cent. 



Oi T PC. 9 t)-t\ 



U „ 13-0 „ 22-G 



13-6 „ 19 

 13-0 „ 22-i 

 12-0 „ 28-6 



With the two larger sized openings the flame was perfectly steady, 

 with the 2 inch opening there was a slight flickering caused by the 

 draught ; this was more marked with the li inch opening and was exces- 

 sive with the 1 inch opening, making the flame practically useless as a 

 source of light. It is evident, therefore, that the openings of the globes 

 should be as wide as possible, and not less than 2i inches. The 

 cornelian globes used in Bronner's system of gas lighting have an open- 

 ing of 2| inches diameter, and Sugg has introduced globes of similar 



