Jupiter saw her while she was yet a great way off, and he knew why she had come.  So, to save Io from her, he changed the maiden to a white cow.  He thought that when Juno had gone back home, it would not be hard to give Io her own form again.

But when the queen saw the cow, she knew that it was Io.

“Oh, what a fine cow you have there!” she said.  “Give her to me, good Jupiter, give her to me!”

Jupiter did not like to do this; but she coaxed so hard that at last he gave up, and let her have the cow for her own.  He thought that it would not be long till he could get her away from the queen, and change her to a girl once more.  But Juno was too wise to trust him.  She took the cow by her horns, and led her out of the town.

“Now, my sweet maid,” she said, “I will see that you stay in this shape as long as you live.”

Then she gave the cow in charge of a strange watchman named Argus, who had, not two eyes only, as you and I have, but ten times ten.  And Argus led the cow to a grove, and tied her by a long rope to a tree, where she had to stand and eat grass, and cry, “Moo! moo!” from morn till night; and when the sun had set, and it was dark, she lay down on the cold ground and wept, and cried, “Moo! moo!” till she fell asleep.

But no kind friend heard her, and no one came to help her; for none but Jupiter and Juno knew that the white cow who stood in the grove was Io, whom all the world loved.  Day in and day out, Argus, who was all eyes, sat on a hill close by and kept watch; and you could not say that he went to sleep at all, for while half of his eyes were shut, the other half were wide awake, and thus they slept and watched by turns.

Jupiter was grieved when he saw to what a hard life Io had been doomed, and he tried to think of some plan to set her free.  One day he called sly Mercury, who had wings on his shoes, and bade him go and lead the cow away from the grove where she was kept.  Mercury went down and stood near the foot of the hill where Argus sat, and began to play sweet tunes on his flute.  This was just what the strange watchman liked to hear; and so he called to Mercury, and asked him to come up and sit by his side and play still other tunes.

Mercury did as he wished, and played such strains of sweet music as no one in all the world has heard from that day to this.  And as he played, queer old Argus lay down upon the grass and listened, and thought that he had not had so great a treat in all his life.  But by and by those sweet sounds wrapped him in so strange a spell that all his eyes closed at once, and he fell into a deep sleep.

This was just what Mercury wished.  It was not a brave thing to do, and yet he drew a long, sharp knife from his belt and cut off the head of poor Argus while he slept.  Then he ran down the hill to loose the cow and lead her to the town.

But Juno had seen him kill her watchman, and she met him on the road.  She cried out to him and told him to let the cow go; and her face was so full of wrath that, as soon as he saw her, he turned and fled, and left poor Io to her fate.