•It 



REPORTS ON THE STATE OF SCIENCE. 



1' 7 ruD) allied constant in resistance, aud that from IbD" to l'J03, '26S 

 and 281) remained constant. In 1903 the N.P.L. mercury standards of 

 resistance were constructed, and since then the mercury standards have 

 been taken as constant, and the resistances of all coils expressed by 

 means of them. The B.A. unit (as obtained from all the platinum- 

 silver coils, taking the values given in 1888 as correct, and applying 

 corrections for estimated changes in the coils) was in 1903 found to 

 be equal to 1/1-01367 international ohm. Accepting this ratio for the 

 time being, the resistances at 16°-0 C. of certain coils, comjiared in 1888, 

 1894, 1897, 1903, and 1908, are given in the following table :— 



Table IX. 



* The resistances of these coils are given in ohms (1 ohm = 1-01358 B.A.U.). The remain- 

 ing coils have their resistances given in B.A. miits. 



For the loan of coil No. C4 we are indebted to Professor Trouton, of 

 ITniversity College ; originally this coil was in the possession of Professor 

 Carey Foster. For the loan of the coils numbered 19, 68 (H), 1 C.F.T., 

 34, 3, 4, and 10 C.F.T. we are indebted to Mr. H. A. Taylor, of Victoria 

 Sti-eet, London. We tender our hearty thanks to Professor Trouton and 

 j\[r. Taylor. All the coils, excepting 19 and 34, are of platinum-silver ; 

 1 9 and 34 are of gold-silver. 



In Table IX. maximum differences of the order 1 to 5 parts in 

 100,000 may prol)ably be neglected if this maximum difference does not 

 occur in the period 1903-1908. In 1903 and 1908 the errors of observa- 

 tion were very small, and a recorded difference of 1 or 2 parts in 

 1 00,000 must be taken as indicating a true change in the resistance of a 

 coil. The method of measuring a very small change in resistance will be 

 made clear in the next section on manganin coils. 



The most constant coils appear to be 270, 288, 289, 10 C.F.T., 3, and 

 3715. Of these six resistances two only are unit coils; the remainder 

 are coils of 10 ohms each. In Table IX. the values of eight unit coils 

 and of five 10-ohm coils are tabulated, and of the latter four have kept 

 nearly constant. This fact is important, as it points to the changes of 

 resistance being largely due to actions at the soft-soldered joints, and 

 not entirely, if at all, to the action of paraffin wax (possibly acid) on 

 platinum-silver. In addition, part of the changes may be due to change 

 in structure of the alloy. 



The values at 16^0 C. of the coils A, B, C, D, E, F, G, H and Flat, in 



