ON BALANCES. 



BY H. W. CHISHOLM. 



1. BEFORE proceeding to describe the several kinds of ba- 

 Idnces, and the mode of using them for scientific purposes 

 I propose to call your attention to the principle of the balance 

 and object of its use. 



The balance, whether in its simplest form or with its most 

 elaborate additions, is the instrument universally employed 

 for weighing bodies, or, in more scientific language, for mea- 

 suring their mass. For this purpose the weight of the body 

 is compared by means of the balance with another body of 

 known weight, such as a standard weight or a duly authen- 

 ticated copy. 



2. All weights are referred to one standard or unit of 

 weight, and are stated in numerical terms of this unit, or of 

 one of its multiples or parts. In this country the unit of 

 weight is the imperial standard pound avoirdupois. It is made 

 of platinum, and is in my legal custody as Warden of the 

 Standards. It is kept, together with the unit of length, the 

 imperial standard yard, which is a bar of bronze, in a fireproof 

 iron chest in the strong-room of the Standards Office, 7, Old 

 Palace Yard, "Westminster. The standard pound is not 

 allowed to be taken from its place of deposit except on very 

 special occasions. But I can here show you a facsimile of it, 

 a copy in platinum-iridium, composed of ten parts of iri- 

 dium to ninety parts of platinum. This alloy is a much 

 better material for a primary standard weight than platinum, 

 as platinum is a soft metal and liable to injury, whilst pla- 

 tinum-iridium is harder than steel. Platinum-iridium has 

 been selected by the International Metric Commission at 

 Paris as the material for the new international metric stan- 



