498 



Marvels of the Universe 



been traced between the Sun's spot actix'ity and terrestrial changes ; and this connection is one 

 that, as a general rule, does not affect the interest or comfort of the world at large. It is, of couree, 

 generally known that the magnetic needle does not point directly to the true geographical north, 

 and that the amount of the deviation changes slowly from year to year. It undergoes also a slight 

 change in the course of each day, moving a little westward in the afternoon, and eastward again 

 during the night and morning. The amount of this daily movement varies with the time of the 

 year, being greatest in summer-time ; it varies also from year to year, being greatest in years when 

 there are many spots. But besides this daily range the magnetic needle is also subject to sudden 

 disturbances of a very remarkable character, and these also are connected with some action by 

 the Sun, an action which is often closely connected with the outbreak of a great spot. Thus on 

 February 13, 1892, when the great Sunspot shown in the photograph on page 433 was on the disc, 

 the needles in the magnetic observatories all over the world suffered simultaneously a sudden 

 twitch, after which they began to move rapidlv backward and forward, instead of following their 



usual slow, dignified oscillation 

 once in the twenty-four hours. 

 A month later the rotation of the 

 Sun upon its axis brought the 

 same spot round a second time to 

 the same apparent position upon 

 the disc, and immediately a fresh 

 convulsion seized the magnetic 

 needles. More recently still a 

 yet greater disturbance occuri'ed 

 on September 25, 1909, when 

 for several hours the submarine 

 cables all over the world ceased 

 working, and this coincided with 

 the presence of a very beautiful 

 and active spot, though not one 

 of the largest size. Such dis- 

 turbances are due to streams of 

 minute invisible particles shot 

 forth from restricted areas of the 

 Sun — most frequently areas in 

 which Sunspots have formed or 

 are forming — and driven out in long rays through space. From time to time one of these rays 

 will overtake the earth in its revolution round the Sun, and strike it on the sunset side, producing 

 instantaneously a disturbance of the magnets all over the world. 



Pholo bii] 



A WATER FLEA 



Water Fleas are relatives of th 

 throughout in armour. Xnis species is Daphni. 

 space of the freshwater pond. Its shell is so fi 

 little creature is distinctly seen. 



[J. //. Vrohlree. 



lobsters and crabs, and, like them, are clad 

 k'hich prefers the deeper, clearer 

 that the whole structure of the 



WATER FLEAS 



BY K. G. BL.\IR, B.SC. 



If a sample of the water contained in almost any pond be taken home for examination at leisure, 

 careful inspection in a good light, even without the aid of a magnifying glass, will almost certainly 

 reveal a number of small organisms, the largest not so big as a pin's-head, swimming about, especially 

 against the sides of the vessel containing them, in a series of sharp, jerky movements. Amongst 

 these are sure to be the minute crustaceans — relatives of the lobsters and crabs — popularly known 

 as Water Fleas, and a good pocket lens should enable the observer to recognize one or more of the 

 kinds here illustrated. Of these Daphnia usuall}' prefers the deeper clear spaces of the pond, coming 



