29(5 Sit* John Robison on the best Method of 



according to circumstances, but will always be of greater 

 amount than is generally supposed. 



The experiments made by Drs Turner and Christison serve 

 to shew, that much smaller chimneys than those usually em- 

 ployed, are required to burn the gas to the best advantage. 

 Unfortunately, however, the dimensions most favourable to 

 economy in one respect, are beyond the limits of economy in 

 another ; and when the glasses are made small enough in dia- 

 meter to obtain the maximum of illuminating effect, they are 

 liable to be softened by the heat ; or to be cracked, if not ac- 

 curately centered. A compromise between the two evils must 

 therefore be made, and if this be judiciously done, a great im- 

 provement on the usual routine practice may be effected, a more 

 beautiful and steady light be obtained at a less cost, and our 

 domestic comfort be increased, by the diminution of the heat and 

 effluvia of the gas. 



For practical purposes, therefore, the following directions 

 may be observed. 



Whatever diameter is given to the burner, the glass chim- 

 ney should not exceed it by more than half an inch at the 

 iitmost. If the burner be less than three-fourths of an inch 

 in diameter, the chimney-glass should not exceed li inch in 

 internal diameter. In any case, its height should be no more 

 than four inches above the mouth of the burner from which 

 the jets spring. 



The smallness of the interval which is in this way allowed 

 between the flame and the glass, renders it necessary that the 

 workmanship of the supporting gallery be accurate, in order 

 that the chimney may be held perpendicular, and truly concen- 

 tric with the flame. Gas-fitters rarely give sufficient atten- 

 tion to this imj)Ortant point, and a large share of the expense 

 from broken glasses is owing to defects in this particular. 



In the ordinary mountings, the gallery is put on the burner, 

 which it seldom fits accurately, the glass likewise rarely fits 

 tight into the socket of the gallery, and from these two causes, 

 it is often so much oflF the centre, or so far from being upright, 

 that the flame cannot be raised to a proper height without risk 

 of breaking it. This risk may be greatly diminished by a 

 little change in the disposition of the burner and gallery. In- 





