724 Marvels of the Universe 
Everyone knows how easy it is to detect a telegraph line seen against the background of the 
sky. Not everyone knows that to a person of normally good sight such a wire can be perceived at 
a distance from it of two hundred thousand times its breadth ; or to use a technical expression of 
the astronomer, “ It subtends an angle of one second of arc.’ So in September, 1896, a long 
stream of spots was seen on the sun, that to the naked eye appeared a long, straight, narrow 
gash on its surface ; but in a good astronomical telescope the long, straight line resolved itself 
into scores of spots, separate and distinct, and each full of exquisite detail. 
A single round, black spot can be perceived, if the observer is six thousand times its diameter 
from it ; 7.e., if “ it subtends an angle of thirty-four seconds of arc.’”’ But for fully-defined vision, 
for the object to be truly seen in its actual shape and form, the observer must not be more than 
one thousand seven hundred times its diameter away ; it must “ subtend an angle of two minutes 
of arc.’’ Within this wide range, from one second to one hundred and twenty seconds of arc, all 
small objects will tend to show themselves like 
Martian “ Canals ” and “ oases ’’—that is, as 
straight lines and round dots. 
The two diagrams on page 723 illustrate 
this principle: looked at close at hand, they 
appear utterly different ; but from a distance 
of thirty feet or more they look almost exactly 
alike. The irregular dots and scratches adopt 
the appearance of the straight “ Canals.” 
The nearer we approach an object, the 
better we see it, and increase in the power 
and efficiency of our telescopes effects an 
analogous improvement. 
Schiaparelli, with telescopes of eight and 
eighteen inches aperture—Lowell generally 
used twelve inches—saw “Canals” by the 
score. Barnard, with telescopes of thirty-six 
and forty inches, Antoniadi with one of 
thirty-three, find the spider’s web of straight 
“Canals’”’ giving way to an infinitude of 
CANALS IN MARS? 
The above sketch of the planet, which was made on April 
intricate detail in which there is no hint of 
2nd, 1903, shows the presence of the supposed canals in a Ons 
ruled lines,” or artificial arrangement. 
marked degree. It was made by the late Major Molesworth when 4 ; 
Mars, under good conditions, was seen through a telescope of Finally, photography with the great five-foot 
cig BUUn cic eke peiture: reflector of the Mt. Wilson Observatory has 
added its word, and the restless canal-diggers of Mars have gone to join the gnomes and fairies, 
the trolls and kobolds of our dead mythologies. 
WATER BUGS 
BY EDWARD STEP, F.L.S. 
Bucs, in the entomological sense, are insects that are continuously active throughout life, not 
changing their form, but developing four wings which are fully formed and usable only in the last 
phase ; and whose mouth-parts take the form of a fine-pointed rostrum or beak, which they insert 
into the flesh of animals or plants in order to suck blood or sap. This rostrum has a hinge at its 
base which allows it, when not in use, to be folded down under the breast and between the basal 
joints of the legs. This order (the Hemiptera) contains thousands of distinct species, over four 
hundred of them inhabiting Britain. 
