47 



prevent the British Association units from being materially 

 represented by a column of mercury instead of by a coil of wire. 

 This is just what was agreed to in the end. (See the Resolu- 

 tions at the end of the present paper.) 



Altogether, the Congress had seven what were called plenary 

 sittings — that is, meetings of the Congress as a whole. Besides 

 these, there were six sittings of the first section and a larger 

 number of the second and third. 



Three International Commissions were resolved on. The 

 object of the first I have already stated. 



Of the other two, one was for the selection of a standard 

 source of light, the English "candle" and the French "carcel" 

 being both of them unsatisfactory as standards for measuring 

 the power of electric lights. 



The duties of the remaining commission are fourfold : — 



(a) To prescribe a general plan for the observation of atmos- 

 pheric electricity. 



{b) To compile statistics relative to the efficiency of the 

 different systems of lightning conductors, and to the question 

 whether the networks of aerial wires which traverse our cities 

 in connection with telegraphs and telephones are a source of 

 danger, or of additional security. 



(c) To systematise the observation of earth-currents through 

 telegraphic lines. 



They have, also, a fourth duty, for the imposition of which 

 I am to some extent responsible. The circumstances were these. 

 There was exhibited in the Belgian department of the exhibi- 

 tion, by its inventor, M. Van Rysselberghe, a beautiful instru- 

 ment by means of which the heights of the barometer and 

 thermometer, and four other meteorological elements* could be 

 transmitted every ten minutes to a number of distant stations and 

 made to record themselves there, without the assistance of an 

 operator at either the receiving or the sending station ; and 

 only one telegraphic wire was required for the whole six instru- 

 ments whose indications were transmitted. Its practical char- 



* Namely, humidity, depth of water in rain gauge, direction of wind, and velocity of 

 wind. See Nature, October 20, 1881, p. 588, for a fuller description. 



