OPTICAL PROJECTION 



coarse emery cloth pinched upon it with finger and thumb ; 

 this will surround the needle with circular scratches, making 

 it in fact into a fine round file, to be carefully used inside the 

 bore, by which the latter can be made as smooth as glass. 

 This wi 11 in most cases stop the noise. If more light is wanted, 

 we must burn more gas to get it, and the bore may be enlarged 

 with the broach to any size desired, before polishing, if the 

 jet will allow, for it will be found that a certain chamber will 

 only allow of a certain size of bore without noise. 



In making systematic experiments as to the light possible 

 from the oxy-hydrogen jet, I found, therefore, that it was 



essential to employ a larger 

 chamber if it was desired 

 to use a really large bore. 

 And with any jet which has 

 a large chamber, let us 

 suppose it is a circular ca- 

 vity J inch in diameter and 

 the same in depth, a large 

 bore may be used. Very 

 likely, however, after all 

 has been done to clear and 

 polish the nipple, there 

 may still be noise, and this is generally due to eddies in the 

 gases caused by the form of the chamber. This will probably 

 be as in fig. 39, and the sharp corners at A B cause the noise. 

 By tapering off these, especially at B, as shown by the same 

 letters in fig. 40, silence will generally be procured, and this 

 is, therefore, the chamber I have adopted for my mixed gas- 

 jets. With it there is no difficulty in employing nipples T V of 

 an inch in bore, beyond which there appears little, if any, 

 gain in light. Such a chamber and nipple will easily reach 

 700 candles with the photometer, and over 800 has been re- 

 corded. 



The outside of the nipple, however, also claims attention. 



FIG. 39 



FIG. 40 



