The observations of birds were of no little assistance. If the haze hid the land off whose coasts they imagined themselves to be, they could observe the kind of bird which was flying around them. A flight of wild-fowl, a particular breed of sea-bird, the difference in the fauna, and so on, when off such coasts as Scotland, Ireland, Iceland, and Norway, could not fail to assist them greatly. It is true, also, that in their sailing directions they took notice of the whale. Thus, when sailing from Norway to Greenland one should keep at such a distance to the southward of Iceland as to have birds and whales from thence. Similarly, the drift-ice, icebergs, driftwood, floating seaweed, the colour of the sea were all separate units in the whole method which enabled them to perform what they did. The Gulf Stream water, being of a purer blue than the greenish-brown water of the coastal current, must also have assisted them in their long voyages. Like the ancient seamen of the Mediterranean, they relied largely on the sounding lead, and there is a record that Ingolf and Hjorleif found Iceland “by probing the waves with the lead.” [Illustration: PRIMITIVE NAVIGATION OF THE VIKINGS. Finding the ship’s latitude by the shadow of the gunwale.] As to the primitive method, referred to above, for finding the ship’s latitude by observing the shadow of the gunwale, it has been suggested that they might have measured the length of the shadow of the gunwale by marks on the thwart, and determined when the boat lay on an even keel by means of a bowl of water. They could thus obtain a fairly trustworthy measurement of the sun’s altitude. It has been thought possible that the Norwegians might have become acquainted with the hour-glass either from their voyages to Southern Europe, or else by plundering the monasteries. This would enable them to measure the length of day approximately, and so, taken in conjunction with the sun, be able to tell fairly correctly the direction of the cardinal points of the compass.