464 BEPORT— 1882. 



It will be seen from the first of these two Nile tables, that we have maximum 

 heights at 1863 and 1871, years shortly after the epoch of maximum sun-spots, 

 also, subsidiary maxima at 1853, 1866, and 1876, years near the epoch of mini- 

 mum sun-spots. So far, then, the Nile agrees with the European rivers in showing 

 a maximum of height about the time of maximum sun-spots, and a subsidiary 

 maximum about the time of minimum sun-spots, only this subsidiary maximum 

 is greater than for the European rivers already named. 



From the second Nile table it will be seen that the date of maximum heights 

 appears to be latest on those years for which the yearly height is greatest, so that 

 if we plot curves from the two tables, these curves will be found to be very like 

 each other. Now the present year is perhaps not very far removed from a 

 solar maximum, and I am thus induced to think that the Nile may this year 

 be somewhat late in attaining its maximum rise. 



TUESDA Y, A UG UST 29. 

 The following Report and Papers were read: — 



1. Report of the Committee for constructing and issuing iirnctical Standards 

 for use in Electrical Measurements. — See Reports, p. 70. 



2. Suggestions regardinq the Extension of the Practical System of Units. 

 By Dr. C. W. Siemens, F.E.S. 



3. On a new Form of Galvanometer for Measuring Currents and Potentials 

 in Absolute Units. By Professor Sir William Thomson, F.B.S. 



4. On Electric Meters. By C. VEimoN Boys. 



The electric meters to which attention is drawn are the energy meter and the 

 vibrating current meter. The first gives the amount of energy expended by an 

 electric current in any portion of a circuit during a time, the second gives the 

 quantity of electricity that has passed in a conductor during a time. As the first 

 is fully described in the ' Phil. Mag.' of February 1882, 1 do not propose to describe 

 it at length. It consists essentially of two parts — an indicator, showing the rate at 

 which electric energy is being expended at a time, and an integrator, to sum these 

 indications. 



The indicator depends on the principle that the force exerted between two con- 

 ductors — one conveying the main, and the other, of high resistance, carrying a shunt 

 current — is proportional to the energy expended by the current between the points 

 to which the shunt is connected. The shunt circuit consists of a movable solenoid, 

 wound Avitli a great length of fine wire, the upper half in one direction, and the 

 lower half in the opposite direction. This is suspended in the annular space between 

 two fixed solenoids, through each of which the main current passes in the same 

 direction, so that the upper half is drawn in and the lower pushed away from the 

 fixed coils. It is suspended from one end of a beam, and balanced with a counter- 

 weight, and the motion of the beam is resisted by a pendulum-weight. Under these 

 conditions the tangent of the inclination of the beam is proportional to the energy 

 of the current, which may therefore be read off on a straight scale of equal parts. 

 This construction, as I have shown in the paper referred to, absolutely eliminates 

 inequalities due to the movement of the coils. 



The integrating mechanism, which automatically sums the readings given by 

 the indicator, is a development of the 'cart' integrator described in the 'Phil. 

 Mag.' of May 1881. This instrument is an exact mechanical equivalent of the 

 mathematical principle of integration, which it illustrates most perfectly. Though 



