1902.] affecting the Transmission of Electric Waves. 267 



% The first case is that due to the effects of lightning discharges, which 

 may or may not be visible at the station where its effects are noticed. 

 As a rule, with the instruments in normal adjustment, the effect of 

 every discharge is to record a signal, the exceptions being very few. 



The method adopted to observe this was to fit an electrical bell„ 

 worked by the receiving instruments, close to the observer, and at 

 night observe the flashes and note if the bell rang. 



For detailed observations, it was found more convenient to record 

 the effects on the tape, and this was the method subsequently adopted. 

 On the approach of the area of disturbance towards the ship, the first 

 visible indication generally is — the recording of clots at intervals vary- 

 ing from a few minutes to a few seconds ; secondly, the recording of 



three dots with a space between the first two, thus : ( ) or e i, in 



the Morse Code, and this is the sign most frequently recorded by 

 distant lightning; thirdly, the recording of dashes; the intervals 

 between these then gradually decrease and merge into irregular signs, 

 which have sometimes spelt words in the Morse Code; the effects 

 generally die out more suddenly than they appear. 



They are much more frequent in summer and autumn than in 

 winter and spring — in the neighbourhood of high mountains than in 

 the open sea— in southerly than in northerly winds (in the Medi- 

 terranean Sea) — in the front of a cyclonic disturbance of the atmo- 

 sphere than in the rear, and with a falling barometer than with a 

 rising one. In settled fine weather, if present, they reach their maxima 

 between 8 and 10 p.m., and frequently last during the whole night, 

 with a minimum of disturbance between 9 A.M. and 1 p.m. 



The next cause which is intimately connected with the above, is the 

 shorter distance at which signals can usually be received, when any 

 electrical disturbances are present in the atmosphere, compared to the 

 distance at which they can be received when none are present. The 

 distance varies from about 30 to 80 per cent, compared with that 

 obtained in fine clear weather. It does not in any way decrease with 

 the increase of the number of lightning discharges which register their 

 effect on the instruments, at any given time, but rather the reverse, 

 the loss in distance generally preceding the first indications, on the 

 instruments, of the approaching electrical disturbance. 



A very marked case is given as an example : Two ships whose instru- 

 ments were in perfect order, and whose sea-signalling distance was 

 about 65 miles, opened their distance from each other on a fine, calm, 

 bright day ; when they were 22 miles apart, the signals died away, 

 though there was no intervening land or other apparent cause for this, 

 but it was noticed that the barometer was falling ; the ships closed, 

 and got into communication again. Atmospheric disturbances were 

 then registered on both sets of instruments, and on the ships opening- 

 out again, no signals were obtained over 20 miles. The trials were 



