THE LIME-LIGHT 67 



end. Then, by having a perpendicular screw fixed in the board 

 or tray, on which two milled flange nuts screw up or down, 

 embracing the fork between them, the front part of the jet 

 can be easily fixed in any position, either perpendicularly or 

 sideways. This can be applied for five shillings to any jet. 

 For those who prefer it, opticians have also fitted jets like a 

 compound slide-rest, with vertical and two horizontal screw 

 movements. These are useful for optical or microscopical 

 work, but for plain lantern-work worse than useless. The 

 clamp-screw of the jet is not, however, put in the right place 

 by most opticians. It is best near the bottom of the socket, 

 instead of near the top, as usual, where the very act of tighten- 

 ing the screw alters the adjustment. At the bottom, tighten- 

 ing the screw has not this effect. 



I have never found much trouble in fastening the jet with 

 a single screw in the socket. But if there is any, it can be 

 effectually overcome by an expedient pointed 

 out years ago by Mr. Samuel Highley, of 

 filing a flat (fig. 44) on the opposite side of 

 the rod to that on which the screw acts. 

 Just the sharp edges of the flat must, how- 

 ever, be filed off slightly, or they will score 

 the brass socket and hinder adjustment. 



34. Inclination of the Nipple. For slides the nipple 

 should make an angle of 40 to 45 with surface of the lime. 

 For optical work, or for the microscope, where the jet has to 

 be brought nearer the condensers, about 35 is better, or the 

 nipple will cast a shadow on the lower part of the condenser. 

 Both to avoid this, and also because there is a perceptible gain 

 in light, the supporting rod, and consequently the lime, should 

 be inclined forwards about 20 from the perpendicular. This 

 both brings more luminous rays to bear, and takes the nipple 

 gtill more out of the way, and the gain of light is very 

 perceptible. 



It will be seen that there is a great deal to be attended to 



F2 



