On one occasion while crossing the Atlantic in fine weather I noticed, some miles directly ahead of the ship, a long line of glassy water. Small waves indicated that the wind was blowing in the exact direction in which the ship was moving, and as we approached the glassy line, the waves became smaller and smaller until they completely disappeared in a mirror-like surface, which was about 300 or 400 feet wide, and extended both to the port and starboard in approximately a straight line as far as the eye could reach. After passing the centre of this zone, I noticed that small waves began to show themselves, but in the exact opposite direction to those through which we had already passed, and these waves became larger and larger for nearly half an hour. Then they began to get gradually smaller, when I observed another glassy line directly ahead of the ship. As we approached it, the waves again completely disappeared, but after passing through it, the wind was blowing in the opposite direction, and the waves increased in size exactly in the same manner that they had diminished on the opposite side of the glassy streak (Fig. 4). [Illustration: Fig. 4.--Air currents observed in mid Atlantic, warm air ascending at _a_, _a_, _a_, and cold air descending at _b_, _b_, _b_. _c_, _c_, _c_ represent the lines where the waves were the largest]. This, of course, shows that directly over the centre of the first glassy streak, the air was meeting from both sides and ascending in practically a straight line from the surface of the water, and then spreading out high above the sea, setting up a light wind in both directions. I spent the winter of 1890-91 on the Riviera, between Hyères les Palmiers and Monte Carlo. The weather for the most part was very fine, and I often had the opportunity of observing the peculiar phenomena which I had already noticed in the Atlantic, only on a much smaller scale. Whereas, in the Atlantic, the glassy zones were from 8 to 15 miles apart, I often found them not more than 500 feet apart in the bays of the Mediterranean. This was most noticeable at Antibes (Fig. 5), very good photographs of which I obtained. It will be observed that the whole surface of the water is streaked like a block of marble. [Illustration: Fig. 5.--Glassy streaks showing the centres of ascending and descending columns of air in the Bay of Antibes, Alpes Maritimes.]