December i2ih, iQi6.] PROCEEDINGS. xi 



Ordinary IMeeting, December 12th, 191 6. 



Professor W. W. Haldane Gee, B.Sc., AI.Sc. Tech., 

 Vice-President, m the Chair. 



Mr. W. G. Pemberton made a short communication on 

 **A direct reading Specific Gravity Balance for Solid Bodies 

 heavier than water." 



If a penduhim be furnished with a circular head, and be 

 swung' on a pivot passing through the centre of the circular 

 headpiece, it may be used, with a suitable scale, as a direct 

 reading Specific Gravity Balance. 



The body under examination is hung on a thread which 

 passes round a groove in the circular head, and a sliding weight 

 is adjusted along the pendulum arm until equilibrium is ob- 

 tained with the latter horizontal. {Fig. /.) 



A vessel of water is then introduced around the sample, 

 and the pendulum falls back through a certain angle to a 

 position of rest. 



Now from Fig. i. 

 Where M is the mass of the sample. 

 And K is the radius of the circular head. 



Where W is the mass of the pendulum and sliding weight. 

 And L is the distance from the pivot at which it may be 



assumed to act. 



MR = WL :. M^- /^^. 



R 



And from Fig. 2. 

 Where Mj is the weight of the sample in water. 



;i/, A' = ; FZ cos 9 M^ = ^^ cos (^. 



Now the specific gravity of any body 



weight in air 



weight in air - weight in water 



WL 



M _ R I 



M - Af, WL WL cos ~ 1 - cos i) 



R /< 



Therefore the specific gravity varies only as the angle 

 and the mass or position of the sliding weight will cause no 

 difference in reading, if a scale be constructed from the equa- 

 tion. 



c P _ I - cos9 

 I 

 giving- direct readings of the .S. G. from the angle fi. 



