Bauhaus-Universität Weimar

Optical Projection: A Treatise of the Use of the Lantern in Exhibition and Scientific Demonstration
Wright, Lewis
rotated by the cog-movement on a screwed pin, it not only 
has a tendency to stick fast, but it scarcely rises witli an entire 
revolution, and the movement has to be continued for many 
rapid revolutions to bring a fresh ring of the lime surface into 
play. Hence a good ‘ blow-through,’ or oxy-gas jet, will often 
equal the light of such a mixed jet. The performance can be 
greatly improved by clearing out the gauze to leave a free 
passage, and attending to the jet as presently described. But 
more than 350 candles can scarcely be got from such jets, and 
with this gain in power the inconvenience of adjusting the 
lime becomes much greater, as it has to be oftener made. 
A good lime-turning movement should raise the lime 
sufficiently, at every revolution, to bring the required new 
zone before the jet. 
What is called the ‘ improved ’ arrangement amongst 
London opticians answers fairly well, the cog wheel being 
made to turn a barrel with a square hole, through which the 
squared lower end of the lime spindle slides freely, whilst a 
treble-threaded screw on the upper part works in the brass 
frame of the combination. The mixing-chamber into which 
the gas-tubes deliver the gases is also rather larger in these 
jets, which can often be made to give a very good light, 
especially by taking out the gauze. If they do not, or if more 
light is desired, or if, as is often the case, they whistle or roar 
under good pressure, they must be attended to, and it is always 
worth while to spend a little trouble over a well-made jet. The 
tap-plugs should be taken out to see that they are not choked 
by tallow, as is sometimes the case. Whistling or roaring is 
generally due to some roughness in the nipple, or end of the 
tube bearing it. To remove this the nipple should be taken 
off, and a watchmaker’s broach twirled round in it, which will 
smooth out the bore itself ; and any roughness in the larger 
bore below, or at the end of the tube, should also be cleaned 
down with a tapered steel rimer. Finally a steel needle should 
be taken, rather smaller than the bore, and twirled well between


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