420 Notes. 



even become somewhat tilted in the opposite direction — with the 

 result that less heat is given to the stage, the stage cools some- 

 what, and the cycle of events re-commences. 



It will have appeared from the last paragraph that the con- 

 struction of the beam and its component parts is of some im- 

 portance. The beam itself is made of magnalium — a newly- 

 discovered alloy of magnesium and aluminium, which is rigid and 

 of low specific gravity — in order to re-act readil}' to slight varia- 

 tions in weight at either end. In commencing work, the beam is 

 so adjusted by means of the adjustable weight and the silk thread 

 attached to the float, that when the entire weight of the float is 

 acting the beam is inclined downwards towards the stage, and the 

 bent portion of the silver rod is well immersed in the paraffin ; 

 when the iron float is supported, the inclination of the beam is 

 such that the silver rod is just above the level of the paraffin, 

 and when the float just touches the surface of the mercury, the 

 beam is horizontal. 



Having arranged the beam satisfactorily, the glass tap con- 

 nected with the glass bulbs is turned full open, and heat is applied 

 to the silver rod. As soon as the desired temperature has been 

 reached, as indicated by a thermometer inserted in one side of the 

 stage, the glass tap is turned off, and the oscillations about that 

 temperature commence. The stage shown had been kept at a 

 temperature not varying more than l°on either side of 100° F. day 

 and night for a week. 



In describing the apparatus (fig. 84, pi. VIT.) the author referred 

 to many difficulties met with during its evolution, and particu- 

 larly that dependent upon the existence of an irregular expansion 

 of copper about the temperature of 100° F. It was this which 

 necessitated the employment of glass bulbs to contain the air, in- 

 stead of allowing the stage itself to act as the air-containing closed 

 box connected with the manometer. 



The Bunsen burner for the apparatus is of a new model, being 

 provided with a safety cock for shutting off the gas in case of 

 accidental " firing back." This cock is situated close to the base 

 of the burner on the horizontal tube, and is provided with a long 

 arm, to which a spring is attached. This arm is soldered with 

 soft solder to the bottom of the vertical tube of the burner, and 

 in this position the gas is full on and the spring is stretched. 

 If the Bunsen fires back, the lower part of the burner becomes 

 rapidly heated, the solder melts, and the recoil of the spring turns 

 the cock and shuts off the gas. 



The author acknowledged the great help he had received in the 

 preliminary stages from Mr. W. T. Hillier, M.R.C.S., his former 

 assistant in the Cancer Research Laboratories of the Middlesex 

 Hospital, and from Mr. Swift, of Tottenham Court Road, who 

 made the finished apparatus from rough models and drawings. 



