484 
THE EARL OF BERKELEY AND MR. E. G. J. HARTLEY ON THE 
them to receive the brass rings 00, which in their turn are perforated by screw holes 
to receive the thumb screws PP, by means of which, together with a rubber washer, 
a tight joint is made between the flanges QQ of the curved metal tubes YY and the 
ends of E and F. The uses of these tubes will be explained later. 
The perforation If is for filling the apparatus with solution, and also for connecting 
to the pressure apparatus, while S serves to empty the vessel. The method of 
making a pressure-tight joint, shown at It, originated, we believe, at the Cambridge 
Scientific Instrument Co. It may be useful to call attention to it, as we have 
experienced no trouble, although the joint has been made and remade over a 
thousand times. It is scarcely necessary to describe the joint, as the diagram 
illustrates it sufficiently; the only point to emphasize is that the thread on the steel 
pressure tube T should be of a smaller pitch than that on the outside of the nut. 
The Beam Pressure Apparatus. 
The pressure apparatus described briefly in our preliminary communication had to 
be modified because it was found that the dermatine-ring stuffing box therein 
mentioned was unsatisfactory, and also because the necessarily somewhat large leak 
past the stuffing box (this was unavoidable, for, if checked, the plunger was no longer 
free) made it imperative to adjust the beam continuously—a labour which sometimes 
lasted without intermission from 10 A. m. to 7 p.m. 
The new form was made for us by the Cambridge Scientific Instrument Co., and is 
shown in elevation and plan in Diagrams 1 and 2 respectively. 
