722 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1912. 



position. Icebergs are often in an exceedingly unstable state, and 

 the slightest increase in wind or sea disturbance causes them to break 

 up or turn over. This is one of the reasons why captains always go 

 as far away from them as possible. (See the Appendix.) 



SIGNS OF THE PROXIMITY OF ICE. 



Since the earliest days efforts have been made to find some means 

 of detecting the presence of ice. To those who have had many years* 

 experience in navigating in the ice region the presence of ice is 

 made known by a number of effects. Before ice can be actually 

 seen there is a peculiar whiteness observed around the berg on a dark 

 night, except in the case of dark bergs. This is called by mariners 

 the ice "blink." It is caused by the reflection of the scattered rays 

 of light from the sky from the white surface of the berg. Thus it 

 is a contrast between the black absorbing water, which reflects none 

 of the light, and the ice, which scatters nearly all. A dark berg is 

 one casting a shadow toward the ship. When the light comes more 

 strongly from any particular part of the sky the iceberg often can not 

 be seen in certain directions, while clearly visible by the ice blink in 

 others. This I believe to be the reason why the officers on the 

 Titanic did not see the berg soon enough to stop. It is stated that 

 on a clear day on the horizon over the ice the sky mil be much paler 

 or lighter in color, and may be distinguished from that overhead. 



During foggy weather ice can sometimes be made out on account 

 of its darker appearance. In this case it is a contrast effect again, 

 but this time it is the shadow of the berg against the white shadow- 

 less fog particles. 



Icebergs are sometimes detected by the echo from the steam 

 whistle or foghorn. They are also frequently heard for many miles 

 by the noise they make in breaking up and falling to pieces. The 

 cracking of the ice or the falling of the pieces into the sea causes a 

 noise like thunder. 



The absence of swell or waves is sometimes a sign of ice or land, 

 and the presence of flocks of birds far from land is an indication of 

 ice. The temperature of the air usually falls as ice is approached, 

 and mariners describe a peculiar damp cold as distinguished from 

 the cold caused by a change of wind. I shall discuss the fall in 

 temperature of the sea as ice is appoached in what follows. 



FAILURE OF PREVIOUS EFFORTS TO MAKE USE OF TEMPERATURE 

 CHANGES IN THE SEA. 



Navigators place no reliance on temperature measurements. As 

 a matter of shipboard routine, the temperature of the water is taken; 

 but very Uttle, if any, attention is taken of it. The method is to dip 



