146 , BEPOET— 1886. 



Messrs. Elliott Bros, called the attention of the Secretary, during the 

 spring of the current year, to the fact that in some of the coils the 

 paraffin used for insulation acquii-ed in time a greenish tinge, which is 

 most marked round the interior of the case and round the places at which 

 the copper of the connecting rods comes in contact with the paraffin. 

 Careful examination shows this green tinge in almost all the coils, and 

 an analysis of the paraffin made by Mr. Robinson, of the Chemical Labo- 

 ratory, Cambridge, proved the colour to be due to a very slight trace of 

 copper. The insulation resistance of several of the standards was, there- 

 fore, tested by passing the current from 24 Leclanche cells through a high 

 resistance galvanometer, and the coil from the case through the paraffin 

 to the wire. This resistance for most of the coils tested was found to be 

 from eight thousand to ten thousand megohms. One coil in particular, 

 sent by Messrs. Elliott, in which the gi-een coloration was most marked, 

 had a resistance of 5000 megohms. Thus it is clear that the resistance 

 of the coils is not hitherto seriously affected by the presence of the copper 

 in the paraffin, but at the same time it becomes necessary to watch closely 

 for any changes which may occur, and to select very carefully the material 

 used. There appears to be great difficulty in getting rid of all the acid 

 employed in the manufacture of the paraffin. 



The only coil among those tested which showed an insulation resist- 

 ance, so low as to be serious, was the one known in the Reports as Flat. 

 When the galvanometer of 1700 ohms resistance was shunted with 4 ohms 

 a deflection of 80 divisions on the scale was obtained. The same deflec- 

 tion was obtained when the resistance in circuit was a megohm and the 

 shunt was about 20 ohms. Thus the insulation resistance of Flat was 

 only about i megohm, or 200,000 ohms. 



Two coils of special interest have recently been sent to be tested. 

 One from Pi^of. Himstedt, of Freiburg, will connect his determination of 

 the ohm with those made in Cambridge ; while the second is a coil of 

 10 B.A. units from the Johns Hopkins University, which has been com- 

 pared with the coils used in the determination of the ohm there. The 

 results of the observations on these coils are, however, not yet com- 

 pletely worked out. 



The Committee wish to express their sense of the great desirability 

 of establishing a National Standardising Laboratory for Electrical In- 

 struments on a permanent basis, and their willingness to co-operate in 

 the endeavour to secure the same. 



The Committee have had under consideration the question of the 

 means to be taken to secure the general adoption of the Resolutions of the 

 Paris Congress. 



The Committee have received by the kindness of the French Govern- 

 ment a specimen of the platinum iridium wire, of which it is proposed 

 that the French National Standards of resistance should be constructed. 

 They hope shortly to make a aeries of measurements of its specific resist- 

 ance and temperature coefficient. 



In conclusion they would ask to be reappointed, with the addition of 

 the name of Mr. J. T. Bottomley and a grant of 501. 



