I. On a new form of the 'sprengel' air-pump and vacuum-tap

Having had the honour of being with Mr. Crookes during the whole of his recent researches on Radiation, and knowing the importance of obtaining the highest degree of rarefaction possible, I have latterly devoted much attention to the improvement of the “Sprengel” mercury-pump. Having now succeeded in constructing an instrument yielding very satisfactory results both in degree of exhaustion and rapidity of working, I purpose giving a detailed description of it, together with a new form of vacuum-tap which has been found exceedingly useful while working with vacua. The instrument, owing to the number of accessories, at first sight appears complicated. I will therefore first explain the principle of the pump, tracing the mercury and exhaustion through the different tubes, and then describe each adjunct separately.