2 Mr Ri(d[/e, A self- recording electrometer 



stations to be chosen as far removed as possible from the disturbing 

 influence of manufacturing operations, and of railways, and it was 

 intended to have taken a set of observations in the neighbourhood 

 of the Dead Sea, as in that district, stations for the instruments 

 might have been chosen with altitudes varying from 1400 ft below 

 sea level to 3000 ft above, and in an open country. As a number 

 of instruments were required it was necessary to keep the cost of 

 construction low, and this has been achieved in the instrument to 

 be described, so that the cost of material is less than ten shillings 

 and a moderate amount only of mechanical skill is required in the 

 construction. 



The complete apparatus consists of: 



(1) The Electrometer. 



(2) The recording cylinder. 



(3) The illuminating arrangement. 



(4) The charging battery. 



(5) The collecting system. 



(1) The Electrometer. This consists of four curved pieces of 

 brass cut from a tube of 3 cm. diameter, and attached to a block of 

 ebonite. The alternate pieces were connected together in the usual 

 way. Each conductor subtended an angle at the centre of the 

 mirror of about 60°, and the adjacent conductors were about 

 1 mm. apart. The " needle " was formed from a piece of silvered 

 paper, 2*5 x 1"5 cm. carrying a small mirror, or a piece of silvered 

 thin "cover" glass could be used for both needle and mirror. A fine 

 wire was attached to the needle to support a piece of wire gauze 

 which was immersed in a small bottle containing paraffin oil, for 

 damping the motion of the needle. The system was suspended by 

 a fine phosphor bronze wire by means of which the needle could be 

 charged, Fig. 1. The whole was enclosed in a thin wooden case 

 having a small window in front, and ebonite plugs to allow of 

 connection being made to the quadrants. 



(2) The recording cylinder. This is the most novel feature of 

 the instrument, and is constructed from one of those small round 

 clocks which may be bought from a shilling upwards. Two sizes 

 of clock-case are common, of diameters 10 cm. and 6 cm., and both 

 of these sizes have been used. A brass tube is substituted for the 

 hour hand at the fi'ont of the clock, and a similar piece of brass 

 tubing is attached to the arbor at the back of the clock, which is 

 attached to the minute hand and used for setting the clock. These 

 two tubes are in the same straight line and furnish a convenient 

 axis about which the clock as a whole can rotate. If the tube 

 attached to the hour hand is fixed, the clock-case will turn round 

 once in twelve hours, whilst if the minute hand is fixed, the clock 



