gise'lurs, tubes made of very hard glass, containing highly rarefied gases, as air, oxygen or nitrogen. Each end of the tube has a platinum wire sealed into it, to serve as an electrode. When a discharge of electricity is caused to take place in these tubes, by connecting the electrodes to the terminals of a Ruhmkorff's coil or a Holtz's machine, very brilliant effects may be produced. See CROOKES TUBES.