48 



J. F. Tennant — On Standard Weights. 



[No. 1, 



from which I get, by interpolation, as a result of the " weighnent'" 



EI ^ 0, + 1-2 i - P.,,- Ig-orO, + 1-2 ^-0-297 P,, 



The second weighment is made after the weights are interchanged in 

 the pans and the result deduced the same way. These together make one 

 " comparison and then a second comparison is made, every operation being 

 followed, but precisely in the reverse order, to make a " complete compari- 

 son''' The result of the four equations when summed is 

 4 EI = 4 0i + 0-191 P.Qi or 

 EI = Oi + O 04775 P.Qi 

 The interpolations are made with sufficient accuracy with a slide 



rule. 



In all the comparisons of the set and P set, except those of EI 

 with 0^, which were made with the balance Oertling No. 1, I have used 

 one of the riders (the right) to add a constant weight to one side and 

 the other in variable positions. Assuming that the rider can be accurately 

 placed on the divisions, and that these are sufficiently accurate, it seems 

 to me that I may safely use the rider in this way, and that the error of 

 determination of the weight of the rider will thus be of less importance 

 than that of a small weight. 



In the case of the very small weights I have added the weight Poj^ to 

 one pan, and P^* to the other, in order to steady them, with great ad- 

 vantage. 



Sectioit V. — Determination of O-^, in terms of the English 

 Commercial Pound 



I have before mentioned that I have received as a Standard a Troy 

 ounce of Platinum-Iridium, whose weight in terms of the Parliamentary 

 Standard Pound P S. is 47995979 grains of PS.; and I have explained 

 the relations between the English Standard Pound and the commercial 

 Pound. In order that I may determine the errors of the Bullion set of 

 Weights, it is necessary that I should determine 0^ in terms of the English 

 Commercial Pound : I have it is true the determination made in London, 

 but it is necessary to verify this, not only to make the standard of weight 

 now, identical with that I should get again, but also because the gilt 

 weights may have slightly changed in the long voyage. 



The Barometer I have used is an Aneroid Barometer by Brown- 

 ing, which I have found give corrected Barometer readings witlaout 

 sensible error. I have, except in the first comparison, used two Ther- 

 mometers which were examined for me some years ago at Kew, and 

 whose zero point I have recently re-determiiied : these were suspended in 

 the balance case of Oertling No, 1, so as to hang about half way between 



