THOMSON. — ATMOSPHERIC ELECTRICITY. 23 



ought to be taken regularly three or four times a dayj also 

 occasionally during the night to give the observer some practice in 

 the use of a lantern for reading the divisions on the circle and of 

 the vertical scale. 



(2.) When stationary in winter quarters observations should be 

 made three times a day at intervals of six hours ; for example, at 

 8 a.m., 2 p.m., and 8 p.m., or at 7.30 a.m., 1.30 p.m., and 7.30 p.m. 

 Whatever times are most convenient may be chosen provided they 

 be separated by intervals of six hours. 



(3.) It is very desirable that hourly observations should be 

 made, if only for a few days, in winter and in summer. If possible 

 arrangements to do so at least for six consecutive days in winter, 

 and for six consecutive days in summer should be made. The re- 

 sults will be very interesting as showing whether there is a diurnal 

 or semi-diurnal period in either the Arctic winter or summer, 

 as we know there is at every time of year in places outside the 

 Arctic circle. 



(4.) Make occasionally special observations when there is any- 

 thing peculiar in the weather, especially with reference to wind. 



V. Special precautions : 



(1.) In the Arctic climate more care may be necessary than in 

 ordinary climates as to earth connections. Therefore put a piece 

 of metal on the stand on which the electrometer is placed during 

 an observation on board ship, and keep this in metallic communi- 

 cation with the ship's coppers or. lightning conductors. If the 

 electrometer is held in the hand with or without a glove, a fine 

 wire ought to be tied round the brass projection which carries the 

 lens, or otherwise attached to the outer case of the electrometer, 

 and by this wire sufficient connection maintained with the earth 

 during an observation. The connection will probably be sufficient 

 if a short length of the wire is laid on the ice and the observer 

 stands on it. Enough, however, is not yet known as to electric 

 conductivity of ice : and to make sure it may be necessary to have 

 a wire or chain let down to the water through a hole in the ice, 

 and metallic connection kept up by a fine wire between this and 

 the electrometer case during an observation. 



(2.) The observer's cap (particularly if of fur) and his woollen 

 clothing, and even his hair if not completely covered by his cap, 

 will be apt in the Arctic cUmate to become electrified by the slightest 

 friction, and so to give false results when the object to be observed 

 is atmospheric electricity. A tin foil cover for cap and arms, 

 kept in metallic communication by a fine wire with the hand or 

 hands applied to the case of the electrometer or to the micrometer 

 screw head, should therefore be used by the observer (and assis- 

 tant, if he has an assistant to carry lanthorn, or for any other 

 purpose), unless he has made sure that there is no sensible dis- 

 turbance from those causes, without the precaution. 



VI. Instruments, stores, and appliances for observation of atmo- 

 spheric electricity sent with the Expedition : 



1. Two portable electrometers, Nos. 35 and 36, each with one 

 steel wire for carrying match, one charging rod, and one electro- 

 phorus for charging the jar. 



