350 Scientific Proceedings, Royal Dublin Society. 



is represented in its actual dimensions. The float is a sphere of 

 slight blown glass, weighing about 12 grammes, its diameter being 

 about 6-3 cms. The outer vessel is of brass, parting, in a screw- 

 joint, into hemispheres. For convenience of weighing by replace- 

 ment, a double pan of slight brass is attached to the wire. This 

 pan, together with the suspending gear, weighs about 1 1 grammes. 

 The suspending wire traversing the surface of the liquid is of brass ; 

 its diameter is - 09 mm. Its breaking strength is 403 grammes : 

 the stress it is called upon to bear in the balance does not ordi- 

 narily exceed 120 grammes. A suddenly added or removed load 

 might, indeed, act to some extent as a live load, and an increased 

 stress result. Experience, however, seems to show that the strength 

 is ample. 



The balance is protected from draughts and sudden changes of 

 temperature by a glass case, from the roof of which it depends, 

 hanging freely. 1 The weights are introduced at a half door in the 

 lower part of the case. The case needs no levelling screws. 



At 6° C. the load carried in the pan, when equilibrium obtains, 

 is 104'660 grammes. A change of load of 1 milligramme now 

 causes displacement, and effects the descent or ascent of the pan. 

 This balance then estimates the weight of 100 grammes to an 

 accuracy of 100,000. 



I must here observe, however, that working the balance to this 

 degree of accuracy needs some care. Where estimation to an 

 accuracy of say three milligrammes only is needed no special pre- 

 cautions are likely to be required. But with the construction 

 shown in the figure for confining the travel of the pan and float 

 there would seem to be an amount of adhesion before the pan is set 

 in motion, which the small force of one milligramme will some- 

 times be unable to overcome. It is seen in figs. 1 and 2 that the 

 double-eyed link to which the suspension wire is attached moves 

 through — but without contact while moving — an eye which arrests 

 its motion ascending and descending, affording it only about one 

 centimetre run. The float thus never reaches either to the top or to 



1 For very delicate work the further precaution of preserving the whole in a 

 chamber not exposed to sudden fluctuations of temperature is, I find, necessary. 

 Trouble from this source might doubtless be guarded against in all cases by sur- 

 rounding the outer vessel "with a non-conducting covering. 



