1880.] 



J. F. Tennaiit— 0« Standard Weif/Jifs. 



45 



sary changes for units, and for tlie position of Her Majesty's Mint at 

 Calcutta. The density of water has been calculated from a formula similar 

 to Professor Miller's ; but with the constants deduced from the new Tables 

 of the British Standards Office. The otlier Tables, for the expansion of 

 metals, are deduced from the same data as those of Professor Miller, but the 

 form makes them more compact and convenient without any loss of accu- 

 racy. All will be found at the end. 



Section II. — The Balances. 



OertUng Xo. 1 is a chemical balance by Oertling with a beam 365 

 m. m. (14'56 inches) between the extreme knife edges. The principal 

 knife edge is 28 m. m. (I'l inches) long and the smaller ones 16 5 m. m. 

 or 0'65 inches ; all are of agate resting on agate planes. The beam is 

 divided for the use of riders, and I have satisfied myself that the divisions 

 are sufficiently accurate for this purpose. The scale is placed on the lower 

 part of the pillar, and is read by a long index attached to the centre of the 

 beam : this is in my opinion, the best arrangement. 



OertUncj No. 2 is a balance whose beam cai-ries knife edges 404 m. m 

 (15"9 inches) apart. The central knife edge is 38'4 m. m {1^ inches) 

 long and those at the ends, 22 m. m or 0-87 inches. They are all of 

 agate and rest on agate planes. The beam is very strong, and divided with 

 sufficient accuracy for the use of a rider. There is an index of soft iron 

 at each end of the beam to read an ivory scale. The left scale had very 

 fine graduations and appeared to me useless. I have substituted a better 

 one and removed the right scale. 



Section III. — Density of O Set of Weights. 



In order to compare Oi with EI it is necessary to have a density of 

 Oj : I have determined that of Og and assumed it to be the same as that 

 of 0, and of the other O weights. 



It appears from the papers received from the Standards Office that 

 Og = 3 Troy ounces = 1440 grains with sufficient accuracy for this 

 purpose, its exact value will be seen later. 



On July 4th 1879, the balance Oertling No. 1 having been prepared 

 for taking specific gravities, and a platinum hook, intended to support Og 

 in water, having been hung by a fine wire of platinum so as to be immersed 

 in distilled water ; Og was placed in the pan in aii-, and counterlialanced 

 with weights. Og being then placed in the hook, and all air bubbles care- 

 fully removed, it was found that ; X being about 1490-2 grains: 



X ^ Og in water (temp. = 84°. 1) + hook &c. in water + (O.g + 



0.^,1 + 0.y,|- + 0.||„.i) in air + 4. ^ at 10-02 divisions of the scale — 



