Marvels of the Universe 851 
One other concomitant of a total solar eclipse may be mentioned. The Sun being on the farther 
side of the Moon, the Moon casts a shadow into space: that shadow strikes the Earth as the eclipse 
progresses. Observers who are very adroit with their eyes may often catch sight of the shadow 
approaching the place where they are standing, passing over them, and then passing away on the 
opposite side. The sensation is very weird, but so momentary that it often escapes notice. It is 
momentary because the speed with which the shadow traverses the Earth’s surface is one thousand 
eight hundred miles an hour, or about thirty miles a minute. 
In an eclipse of the Moon the total phase comes on very slowly during a period of, it may be, an 
hour or more, and when totality has arrived, though the Moon usually becomes wholly invisible, 
such is not always the case, for sometimes our Satellite’s disc can be traced, exhibiting a ruddy hue. 
This is a matter which seems to depend upon the meteorological condition of the Earth’s 
atmosphere. 
PORCUPINES AND THEIR IMITATORS 
BY R. LYDEKKER, F.R.S- 
THE partial or entire conversion of ordinary hairs into bristly spines, and these again into stout 
horny spines of great strength, is such an obvious and easy method of obtaining immunity from 
the attacks of a large class of foes, that it can scarcely be a matter of surprise to find that it has been 
independently resorted to by several totally distinct groups of warm-blooded quadrupeds. And, 
as if to show us how the process has been accomplished, there is an almost complete gradation from 
ANOTHER TYPE OF CORONA. 
Notice the difference between this and the Corona on the opposite page. The variation in the shape of the Corona is due pre- 
sumably to the prevalence or absence of spots on the Sun. If a total eclipse occurs when the spots are at or near a minimum 
the Corona extends to a much greater distance left and right of the equatorial diameter, as is shown here. If, however, the 
spots are at a maximum the Corona extends more or less equally all round the Sun’s circumference 
