40 BEPORTS ON THE STATE OF SCIENCE. — 1915. 



daylight. If curves be drawn showing the amount of disturbance to 

 telegraphic work from hour to hour, two types of curve stand out : 

 one in which the changes from day to night and night to day conditions 

 are somewhat abrupt, and another in which the changes are much more 

 gradual. The former curves might be called ' trough-shaped,' the 

 latter ' U-shaped. ' The former type is met with at sea and on islands at 

 a considerable distance from the mainland, the other on the mainland, 

 especially in the tropics. The lowest point of the U or of the trough 

 usually falls a little after midday, and the highest point of the convex 

 part of the curve occui's a little after midnight, in nearly all stations 

 north of the Equator. The only exception to this rule is found in some 

 records from Lagos, Nigeria, where the curve showing the intensity of 

 disturbance is lowest about seven in the morning and rises during the 

 daylight hours. Unless local weather conditions are producing great 

 disturbance, the change from night to day conditions and vice versa in 

 stations north of the Equator lags behind the sunrise and the sunset. 

 At some stations south of the Equator, e.g., Cocos Island, the opposite 

 rule seems to be usual. These regular and universal diurnal variations 

 have an average magnitude which is represented on the arbitrary scale 

 used in the Forms by figures like 2 in the day and 5 at night in tropical 

 latitudes, or 0"3 in the day and 3 at night in temperate latitudes. These 

 figures are greatly affected by local meteorological conditions, which in 

 fact frequently overwhelm all the statements set forth above. 



Periods of Excessive Disturbance. 



Occasionally the radiotelegraphic work at a station is rendered almost 

 or quite impossible for a period, by strays of vigour and number greatly 

 exceeding the average. These occurrences are for brevity called 

 ' X storms,' the term ' X ' being an alternative designation for ' stray ' 

 or ' atmospheric' When an X storm happens in the day and lasts 

 more than an hour or two, it may completely alter the character of the 

 curve of that day's disturbances and even make the day poi'tion of the 

 curve higher than the night portion. An analysis of the records has 

 shown that X storms occur within the same two or three days over very 

 wide areas. Occasionally X storms are reported almost simultaneously 

 at places several hundred miles apart, but more usually the X storms 

 occurring at such distances are separated b}'' several hours. Some of 

 the European, American, and Canadian X storms have been compared 

 with the meteorological records and charts for the two continents. 

 The comparison has shown very plainly that periods of severe strays 

 coincide with periods of low barometer, high wind velocity, rapid change 

 of temperature, great rainfall, and, especially, rapid barometer fluctua- 

 tions. In low latitudes the barometer fluctuations during violent X 

 storms can usually be followed on any ordinary instrument. The worst 

 X storm in the European records was accompanied by the rapid move- 

 ment of a low-pressure system in a north-easterly direction. In 

 twenty-four hours the eye of the cyclone moved from a point south-west 

 of Lisbon to the North Sea, and in another twenty-four hours into 



