18 



THE ROYAL SOCIETY OF CANADA 



poise. In oi'der to adjust the needle to any position with reference 

 to the pointer or boom, the sleeve X can turn on the sleeve Z and is 

 clamped in position by the screw Y. The counter-poise is just a little 



€ 



Countcri/veight 



^Stirrup pwotcd lo X 



Poi 

 Slee^/e X 



Po I nle r 



Y 



Sleeve Z 

 ÇiULrlz lube 



more than sufficient to balance the boom, but is prevented from falling 

 below the horizontal position by a stop. This arrangement permits 

 the end of the boom to be depressed without disturbing the needle, or 

 bending the suspension. 



The weight of the different parts in grammes is — 



Weights. 



One vane 0-61 g. 



0-62 g. 



Boom, counterpoise, needle rod, etc 8-23 g. 



Damping vane 0-57 g. 



Total 10.03 g. 



This shows then that the addition of the second vane only adds 

 6% to the weight and permits as fine a suspension to be used for the 

 two vanes as for one. 



Two views of the completed instrument removed from its case 

 and one view with it in its case are shown in plates I and II figs. 

 2. 3 and 4. 



