Introduction and Preliminary Remarks — General Principles to be observed in Glass Working — Choice of apparatus-tools and Appliances — Glass. Glass-blowing is neither very easy nor very difficult there are operations so easy that the youngest laboratory boy should be able to repeat them successfully after once having been shown the way, there are operations so difficult that years are needed to train eye and hand and judgment to carry them out; but the greater number of scientific needs lie be tween these two extremes. Yet a surprisingly large number of scientific workers fail even to join a glass tube or make a T piece that will not crack spontaneously, and the fault is rather one of understanding than of lack of ability to carry out the necessary manipulation.