134 



GASOMETERS. 



by the vessel itself. In a well-constructed apparatus both pressures ought to 

 be equal, but I only know of one or two instances where the adjustment is so 

 correct. 



TELESCOPE GASOMETER. 



I now have to speak of the "Telescope Gasometer," so called from being 

 something similar in its action to the lengthening slides of that instrument. 

 They are only used in cases of necessity, arising from confined space or very 

 bad ground. 



The diameters of these vessels will be from thirty to fifty feet, but not more ; 

 their tanks are usually formed of cast iron, which constitutes the principal 

 part of their expense, when compared to those of the simple form. By refer- 

 ence to Plate XVII. the action will be more clearly understood. A A is a 

 cast-iron tank, fifty-one feet diameter and twenty-five feet high, constructed 

 of plates about three feet one inch deep, by five feet wide, strengthened by ribs, 

 and jointed together with flanches and cement in the usual way, as shown in the 

 annexed cut, which is drawn to a scale of three quarters of an inch to the foot. 



Fig. 31. 



