I've seen plenty of three and four aspect paraffin lamps for sale on E-bay, and it always puzzled me why so many of them were lacking the clear glass, even though all the coloured glasses were present and undamaged. Then I bought one myself, complete with the clear glass (albeit with one corner broken off) and found out why. If you leave the clear glass in the rotating sleeve, the only way you can light it is to release the catch, and pull the sleeve up high enough to get underneath it to reach the wick with your match or lighter. Then, of course, if you need to adjust the flame height, you have to go through the same routine - and again when you want to snuff it out, unless you go for the brutal method, adopted by some philistines on the railway, of just slamming it onto the ground, base first. If, on the other hand, you just remove the clear glass and chuck it away, then lighting, adjusting and snuffing out can be done just by swivelling the sleeve round. Why did it take me so long to work that out?